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ckpts/universal/global_step120/zero/12.attention.query_key_value.weight/exp_avg.pt

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ckpts/universal/global_step120/zero/12.attention.query_key_value.weight/exp_avg_sq.pt

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ckpts/universal/global_step120/zero/16.input_layernorm.weight/exp_avg.pt

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ckpts/universal/global_step120/zero/3.attention.dense.weight/exp_avg_sq.pt

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ckpts/universal/global_step80/mp_rank_06_model_states.pt

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ckpts/universal/global_step80/mp_rank_07_model_states.pt

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venv/lib/python3.10/site-packages/sympy/physics/__init__.py

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+"""
+A module that helps solving problems in physics.
+"""
+
+from . import units
+from .matrices import mgamma, msigma, minkowski_tensor, mdft
+
+__all__ = [
+    'units',
+
+    'mgamma', 'msigma', 'minkowski_tensor', 'mdft',
+]

venv/lib/python3.10/site-packages/sympy/physics/hep/gamma_matrices.py

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+"""
+    Module to handle gamma matrices expressed as tensor objects.
+
+    Examples
+    ========
+
+    >>> from sympy.physics.hep.gamma_matrices import GammaMatrix as G, LorentzIndex
+    >>> from sympy.tensor.tensor import tensor_indices
+    >>> i = tensor_indices('i', LorentzIndex)
+    >>> G(i)
+    GammaMatrix(i)
+
+    Note that there is already an instance of GammaMatrixHead in four dimensions:
+    GammaMatrix, which is simply declare as
+
+    >>> from sympy.physics.hep.gamma_matrices import GammaMatrix
+    >>> from sympy.tensor.tensor import tensor_indices
+    >>> i = tensor_indices('i', LorentzIndex)
+    >>> GammaMatrix(i)
+    GammaMatrix(i)
+
+    To access the metric tensor
+
+    >>> LorentzIndex.metric
+    metric(LorentzIndex,LorentzIndex)
+
+"""
+from sympy.core.mul import Mul
+from sympy.core.singleton import S
+from sympy.matrices.dense import eye
+from sympy.matrices.expressions.trace import trace
+from sympy.tensor.tensor import TensorIndexType, TensorIndex,\
+    TensMul, TensAdd, tensor_mul, Tensor, TensorHead, TensorSymmetry
+
+
+# DiracSpinorIndex = TensorIndexType('DiracSpinorIndex', dim=4, dummy_name="S")
+
+
+LorentzIndex = TensorIndexType('LorentzIndex', dim=4, dummy_name="L")
+
+
+GammaMatrix = TensorHead("GammaMatrix", [LorentzIndex],
+                         TensorSymmetry.no_symmetry(1), comm=None)
+
+
+def extract_type_tens(expression, component):
+    """
+    Extract from a ``TensExpr`` all tensors with `component`.
+
+    Returns two tensor expressions:
+
+    * the first contains all ``Tensor`` of having `component`.
+    * the second contains all remaining.
+
+
+    """
+    if isinstance(expression, Tensor):
+        sp = [expression]
+    elif isinstance(expression, TensMul):
+        sp = expression.args
+    else:
+        raise ValueError('wrong type')
+
+    # Collect all gamma matrices of the same dimension
+    new_expr = S.One
+    residual_expr = S.One
+    for i in sp:
+        if isinstance(i, Tensor) and i.component == component:
+            new_expr *= i
+        else:
+            residual_expr *= i
+    return new_expr, residual_expr
+
+
+def simplify_gamma_expression(expression):
+    extracted_expr, residual_expr = extract_type_tens(expression, GammaMatrix)
+    res_expr = _simplify_single_line(extracted_expr)
+    return res_expr * residual_expr
+
+
+def simplify_gpgp(ex, sort=True):
+    """
+    simplify products ``G(i)*p(-i)*G(j)*p(-j) -> p(i)*p(-i)``
+
+    Examples
+    ========
+
+    >>> from sympy.physics.hep.gamma_matrices import GammaMatrix as G, \
+        LorentzIndex, simplify_gpgp
+    >>> from sympy.tensor.tensor import tensor_indices, tensor_heads
+    >>> p, q = tensor_heads('p, q', [LorentzIndex])
+    >>> i0,i1,i2,i3,i4,i5 = tensor_indices('i0:6', LorentzIndex)
+    >>> ps = p(i0)*G(-i0)
+    >>> qs = q(i0)*G(-i0)
+    >>> simplify_gpgp(ps*qs*qs)
+    GammaMatrix(-L_0)*p(L_0)*q(L_1)*q(-L_1)
+    """
+    def _simplify_gpgp(ex):
+        components = ex.components
+        a = []
+        comp_map = []
+        for i, comp in enumerate(components):
+            comp_map.extend([i]*comp.rank)
+        dum = [(i[0], i[1], comp_map[i[0]], comp_map[i[1]]) for i in ex.dum]
+        for i in range(len(components)):
+            if components[i] != GammaMatrix:
+                continue
+            for dx in dum:
+                if dx[2] == i:
+                    p_pos1 = dx[3]
+                elif dx[3] == i:
+                    p_pos1 = dx[2]
+                else:
+                    continue
+                comp1 = components[p_pos1]
+                if comp1.comm == 0 and comp1.rank == 1:
+                    a.append((i, p_pos1))
+        if not a:
+            return ex
+        elim = set()
+        tv = []
+        hit = True
+        coeff = S.One
+        ta = None
+        while hit:
+            hit = False
+            for i, ai in enumerate(a[:-1]):
+                if ai[0] in elim:
+                    continue
+                if ai[0] != a[i + 1][0] - 1:
+                    continue
+                if components[ai[1]] != components[a[i + 1][1]]:
+                    continue
+                elim.add(ai[0])
+                elim.add(ai[1])
+                elim.add(a[i + 1][0])
+                elim.add(a[i + 1][1])
+                if not ta:
+                    ta = ex.split()
+                    mu = TensorIndex('mu', LorentzIndex)
+                hit = True
+                if i == 0:
+                    coeff = ex.coeff
+                tx = components[ai[1]](mu)*components[ai[1]](-mu)
+                if len(a) == 2:
+                    tx *= 4  # eye(4)
+                tv.append(tx)
+                break
+
+        if tv:
+            a = [x for j, x in enumerate(ta) if j not in elim]
+            a.extend(tv)
+            t = tensor_mul(*a)*coeff
+            # t = t.replace(lambda x: x.is_Matrix, lambda x: 1)
+            return t
+        else:
+            return ex
+
+    if sort:
+        ex = ex.sorted_components()
+    # this would be better off with pattern matching
+    while 1:
+        t = _simplify_gpgp(ex)
+        if t != ex:
+            ex = t
+        else:
+            return t
+
+
+def gamma_trace(t):
+    """
+    trace of a single line of gamma matrices
+
+    Examples
+    ========
+
+    >>> from sympy.physics.hep.gamma_matrices import GammaMatrix as G, \
+        gamma_trace, LorentzIndex
+    >>> from sympy.tensor.tensor import tensor_indices, tensor_heads
+    >>> p, q = tensor_heads('p, q', [LorentzIndex])
+    >>> i0,i1,i2,i3,i4,i5 = tensor_indices('i0:6', LorentzIndex)
+    >>> ps = p(i0)*G(-i0)
+    >>> qs = q(i0)*G(-i0)
+    >>> gamma_trace(G(i0)*G(i1))
+    4*metric(i0, i1)
+    >>> gamma_trace(ps*ps) - 4*p(i0)*p(-i0)
+    0
+    >>> gamma_trace(ps*qs + ps*ps) - 4*p(i0)*p(-i0) - 4*p(i0)*q(-i0)
+    0
+
+    """
+    if isinstance(t, TensAdd):
+        res = TensAdd(*[gamma_trace(x) for x in t.args])
+        return res
+    t = _simplify_single_line(t)
+    res = _trace_single_line(t)
+    return res
+
+
+def _simplify_single_line(expression):
+    """
+    Simplify single-line product of gamma matrices.
+
+    Examples
+    ========
+
+    >>> from sympy.physics.hep.gamma_matrices import GammaMatrix as G, \
+        LorentzIndex, _simplify_single_line
+    >>> from sympy.tensor.tensor import tensor_indices, TensorHead
+    >>> p = TensorHead('p', [LorentzIndex])
+    >>> i0,i1 = tensor_indices('i0:2', LorentzIndex)
+    >>> _simplify_single_line(G(i0)*G(i1)*p(-i1)*G(-i0)) + 2*G(i0)*p(-i0)
+    0
+
+    """
+    t1, t2 = extract_type_tens(expression, GammaMatrix)
+    if t1 != 1:
+        t1 = kahane_simplify(t1)
+    res = t1*t2
+    return res
+
+
+def _trace_single_line(t):
+    """
+    Evaluate the trace of a single gamma matrix line inside a ``TensExpr``.
+
+    Notes
+    =====
+
+    If there are ``DiracSpinorIndex.auto_left`` and ``DiracSpinorIndex.auto_right``
+    indices trace over them; otherwise traces are not implied (explain)
+
+
+    Examples
+    ========
+
+    >>> from sympy.physics.hep.gamma_matrices import GammaMatrix as G, \
+        LorentzIndex, _trace_single_line
+    >>> from sympy.tensor.tensor import tensor_indices, TensorHead
+    >>> p = TensorHead('p', [LorentzIndex])
+    >>> i0,i1,i2,i3,i4,i5 = tensor_indices('i0:6', LorentzIndex)
+    >>> _trace_single_line(G(i0)*G(i1))
+    4*metric(i0, i1)
+    >>> _trace_single_line(G(i0)*p(-i0)*G(i1)*p(-i1)) - 4*p(i0)*p(-i0)
+    0
+
+    """
+    def _trace_single_line1(t):
+        t = t.sorted_components()
+        components = t.components
+        ncomps = len(components)
+        g = LorentzIndex.metric
+        # gamma matirices are in a[i:j]
+        hit = 0
+        for i in range(ncomps):
+            if components[i] == GammaMatrix:
+                hit = 1
+                break
+
+        for j in range(i + hit, ncomps):
+            if components[j] != GammaMatrix:
+                break
+        else:
+            j = ncomps
+        numG = j - i
+        if numG == 0:
+            tcoeff = t.coeff
+            return t.nocoeff if tcoeff else t
+        if numG % 2 == 1:
+            return TensMul.from_data(S.Zero, [], [], [])
+        elif numG > 4:
+            # find the open matrix indices and connect them:
+            a = t.split()
+            ind1 = a[i].get_indices()[0]
+            ind2 = a[i + 1].get_indices()[0]
+            aa = a[:i] + a[i + 2:]
+            t1 = tensor_mul(*aa)*g(ind1, ind2)
+            t1 = t1.contract_metric(g)
+            args = [t1]
+            sign = 1
+            for k in range(i + 2, j):
+                sign = -sign
+                ind2 = a[k].get_indices()[0]
+                aa = a[:i] + a[i + 1:k] + a[k + 1:]
+                t2 = sign*tensor_mul(*aa)*g(ind1, ind2)
+                t2 = t2.contract_metric(g)
+                t2 = simplify_gpgp(t2, False)
+                args.append(t2)
+            t3 = TensAdd(*args)
+            t3 = _trace_single_line(t3)
+            return t3
+        else:
+            a = t.split()
+            t1 = _gamma_trace1(*a[i:j])
+            a2 = a[:i] + a[j:]
+            t2 = tensor_mul(*a2)
+            t3 = t1*t2
+            if not t3:
+                return t3
+            t3 = t3.contract_metric(g)
+            return t3
+
+    t = t.expand()
+    if isinstance(t, TensAdd):
+        a = [_trace_single_line1(x)*x.coeff for x in t.args]
+        return TensAdd(*a)
+    elif isinstance(t, (Tensor, TensMul)):
+        r = t.coeff*_trace_single_line1(t)
+        return r
+    else:
+        return trace(t)
+
+
+def _gamma_trace1(*a):
+    gctr = 4  # FIXME specific for d=4
+    g = LorentzIndex.metric
+    if not a:
+        return gctr
+    n = len(a)
+    if n%2 == 1:
+        #return TensMul.from_data(S.Zero, [], [], [])
+        return S.Zero
+    if n == 2:
+        ind0 = a[0].get_indices()[0]
+        ind1 = a[1].get_indices()[0]
+        return gctr*g(ind0, ind1)
+    if n == 4:
+        ind0 = a[0].get_indices()[0]
+        ind1 = a[1].get_indices()[0]
+        ind2 = a[2].get_indices()[0]
+        ind3 = a[3].get_indices()[0]
+
+        return gctr*(g(ind0, ind1)*g(ind2, ind3) - \
+           g(ind0, ind2)*g(ind1, ind3) + g(ind0, ind3)*g(ind1, ind2))
+
+
+def kahane_simplify(expression):
+    r"""
+    This function cancels contracted elements in a product of four
+    dimensional gamma matrices, resulting in an expression equal to the given
+    one, without the contracted gamma matrices.
+
+    Parameters
+    ==========
+
+    `expression`    the tensor expression containing the gamma matrices to simplify.
+
+    Notes
+    =====
+
+    If spinor indices are given, the matrices must be given in
+    the order given in the product.
+
+    Algorithm
+    =========
+
+    The idea behind the algorithm is to use some well-known identities,
+    i.e., for contractions enclosing an even number of `\gamma` matrices
+
+    `\gamma^\mu \gamma_{a_1} \cdots \gamma_{a_{2N}} \gamma_\mu = 2 (\gamma_{a_{2N}} \gamma_{a_1} \cdots \gamma_{a_{2N-1}} + \gamma_{a_{2N-1}} \cdots \gamma_{a_1} \gamma_{a_{2N}} )`
+
+    for an odd number of `\gamma` matrices
+
+    `\gamma^\mu \gamma_{a_1} \cdots \gamma_{a_{2N+1}} \gamma_\mu = -2 \gamma_{a_{2N+1}} \gamma_{a_{2N}} \cdots \gamma_{a_{1}}`
+
+    Instead of repeatedly applying these identities to cancel out all contracted indices,
+    it is possible to recognize the links that would result from such an operation,
+    the problem is thus reduced to a simple rearrangement of free gamma matrices.
+
+    Examples
+    ========
+
+    When using, always remember that the original expression coefficient
+    has to be handled separately
+
+    >>> from sympy.physics.hep.gamma_matrices import GammaMatrix as G, LorentzIndex
+    >>> from sympy.physics.hep.gamma_matrices import kahane_simplify
+    >>> from sympy.tensor.tensor import tensor_indices
+    >>> i0, i1, i2 = tensor_indices('i0:3', LorentzIndex)
+    >>> ta = G(i0)*G(-i0)
+    >>> kahane_simplify(ta)
+    Matrix([
+    [4, 0, 0, 0],
+    [0, 4, 0, 0],
+    [0, 0, 4, 0],
+    [0, 0, 0, 4]])
+    >>> tb = G(i0)*G(i1)*G(-i0)
+    >>> kahane_simplify(tb)
+    -2*GammaMatrix(i1)
+    >>> t = G(i0)*G(-i0)
+    >>> kahane_simplify(t)
+    Matrix([
+    [4, 0, 0, 0],
+    [0, 4, 0, 0],
+    [0, 0, 4, 0],
+    [0, 0, 0, 4]])
+    >>> t = G(i0)*G(-i0)
+    >>> kahane_simplify(t)
+    Matrix([
+    [4, 0, 0, 0],
+    [0, 4, 0, 0],
+    [0, 0, 4, 0],
+    [0, 0, 0, 4]])
+
+    If there are no contractions, the same expression is returned
+
+    >>> tc = G(i0)*G(i1)
+    >>> kahane_simplify(tc)
+    GammaMatrix(i0)*GammaMatrix(i1)
+
+    References
+    ==========
+
+    [1] Algorithm for Reducing Contracted Products of gamma Matrices,
+    Joseph Kahane, Journal of Mathematical Physics, Vol. 9, No. 10, October 1968.
+    """
+
+    if isinstance(expression, Mul):
+        return expression
+    if isinstance(expression, TensAdd):
+        return TensAdd(*[kahane_simplify(arg) for arg in expression.args])
+
+    if isinstance(expression, Tensor):
+        return expression
+
+    assert isinstance(expression, TensMul)
+
+    gammas = expression.args
+
+    for gamma in gammas:
+        assert gamma.component == GammaMatrix
+
+    free = expression.free
+    # spinor_free = [_ for _ in expression.free_in_args if _[1] != 0]
+
+    # if len(spinor_free) == 2:
+    #     spinor_free.sort(key=lambda x: x[2])
+    #     assert spinor_free[0][1] == 1 and spinor_free[-1][1] == 2
+    #     assert spinor_free[0][2] == 0
+    # elif spinor_free:
+    #     raise ValueError('spinor indices do not match')
+
+    dum = []
+    for dum_pair in expression.dum:
+        if expression.index_types[dum_pair[0]] == LorentzIndex:
+            dum.append((dum_pair[0], dum_pair[1]))
+
+    dum = sorted(dum)
+
+    if len(dum) == 0:  # or GammaMatrixHead:
+        # no contractions in `expression`, just return it.
+        return expression
+
+    # find the `first_dum_pos`, i.e. the position of the first contracted
+    # gamma matrix, Kahane's algorithm as described in his paper requires the
+    # gamma matrix expression to start with a contracted gamma matrix, this is
+    # a workaround which ignores possible initial free indices, and re-adds
+    # them later.
+
+    first_dum_pos = min(map(min, dum))
+
+    # for p1, p2, a1, a2 in expression.dum_in_args:
+    #     if p1 != 0 or p2 != 0:
+    #         # only Lorentz indices, skip Dirac indices:
+    #         continue
+    #     first_dum_pos = min(p1, p2)
+    #     break
+
+    total_number = len(free) + len(dum)*2
+    number_of_contractions = len(dum)
+
+    free_pos = [None]*total_number
+    for i in free:
+        free_pos[i[1]] = i[0]
+
+    # `index_is_free` is a list of booleans, to identify index position
+    # and whether that index is free or dummy.
+    index_is_free = [False]*total_number
+
+    for i, indx in enumerate(free):
+        index_is_free[indx[1]] = True
+
+    # `links` is a dictionary containing the graph described in Kahane's paper,
+    # to every key correspond one or two values, representing the linked indices.
+    # All values in `links` are integers, negative numbers are used in the case
+    # where it is necessary to insert gamma matrices between free indices, in
+    # order to make Kahane's algorithm work (see paper).
+    links = {i: [] for i in range(first_dum_pos, total_number)}
+
+    # `cum_sign` is a step variable to mark the sign of every index, see paper.
+    cum_sign = -1
+    # `cum_sign_list` keeps storage for all `cum_sign` (every index).
+    cum_sign_list = [None]*total_number
+    block_free_count = 0
+
+    # multiply `resulting_coeff` by the coefficient parameter, the rest
+    # of the algorithm ignores a scalar coefficient.
+    resulting_coeff = S.One
+
+    # initialize a list of lists of indices. The outer list will contain all
+    # additive tensor expressions, while the inner list will contain the
+    # free indices (rearranged according to the algorithm).
+    resulting_indices = [[]]
+
+    # start to count the `connected_components`, which together with the number
+    # of contractions, determines a -1 or +1 factor to be multiplied.
+    connected_components = 1
+
+    # First loop: here we fill `cum_sign_list`, and draw the links
+    # among consecutive indices (they are stored in `links`). Links among
+    # non-consecutive indices will be drawn later.
+    for i, is_free in enumerate(index_is_free):
+        # if `expression` starts with free indices, they are ignored here;
+        # they are later added as they are to the beginning of all
+        # `resulting_indices` list of lists of indices.
+        if i < first_dum_pos:
+            continue
+
+        if is_free:
+            block_free_count += 1
+            # if previous index was free as well, draw an arch in `links`.
+            if block_free_count > 1:
+                links[i - 1].append(i)
+                links[i].append(i - 1)
+        else:
+            # Change the sign of the index (`cum_sign`) if the number of free
+            # indices preceding it is even.
+            cum_sign *= 1 if (block_free_count % 2) else -1
+            if block_free_count == 0 and i != first_dum_pos:
+                # check if there are two consecutive dummy indices:
+                # in this case create virtual indices with negative position,
+                # these "virtual" indices represent the insertion of two
+                # gamma^0 matrices to separate consecutive dummy indices, as
+                # Kahane's algorithm requires dummy indices to be separated by
+                # free indices. The product of two gamma^0 matrices is unity,
+                # so the new expression being examined is the same as the
+                # original one.
+                if cum_sign == -1:
+                    links[-1-i] = [-1-i+1]
+                    links[-1-i+1] = [-1-i]
+            if (i - cum_sign) in links:
+                if i != first_dum_pos:
+                    links[i].append(i - cum_sign)
+                if block_free_count != 0:
+                    if i - cum_sign < len(index_is_free):
+                        if index_is_free[i - cum_sign]:
+                            links[i - cum_sign].append(i)
+            block_free_count = 0
+
+        cum_sign_list[i] = cum_sign
+
+    # The previous loop has only created links between consecutive free indices,
+    # it is necessary to properly create links among dummy (contracted) indices,
+    # according to the rules described in Kahane's paper. There is only one exception
+    # to Kahane's rules: the negative indices, which handle the case of some
+    # consecutive free indices (Kahane's paper just describes dummy indices
+    # separated by free indices, hinting that free indices can be added without
+    # altering the expression result).
+    for i in dum:
+        # get the positions of the two contracted indices:
+        pos1 = i[0]
+        pos2 = i[1]
+
+        # create Kahane's upper links, i.e. the upper arcs between dummy
+        # (i.e. contracted) indices:
+        links[pos1].append(pos2)
+        links[pos2].append(pos1)
+
+        # create Kahane's lower links, this corresponds to the arcs below
+        # the line described in the paper:
+
+        # first we move `pos1` and `pos2` according to the sign of the indices:
+        linkpos1 = pos1 + cum_sign_list[pos1]
+        linkpos2 = pos2 + cum_sign_list[pos2]
+
+        # otherwise, perform some checks before creating the lower arcs:
+
+        # make sure we are not exceeding the total number of indices:
+        if linkpos1 >= total_number:
+            continue
+        if linkpos2 >= total_number:
+            continue
+
+        # make sure we are not below the first dummy index in `expression`:
+        if linkpos1 < first_dum_pos:
+            continue
+        if linkpos2 < first_dum_pos:
+            continue
+
+        # check if the previous loop created "virtual" indices between dummy
+        # indices, in such a case relink `linkpos1` and `linkpos2`:
+        if (-1-linkpos1) in links:
+            linkpos1 = -1-linkpos1
+        if (-1-linkpos2) in links:
+            linkpos2 = -1-linkpos2
+
+        # move only if not next to free index:
+        if linkpos1 >= 0 and not index_is_free[linkpos1]:
+            linkpos1 = pos1
+
+        if linkpos2 >=0 and not index_is_free[linkpos2]:
+            linkpos2 = pos2
+
+        # create the lower arcs:
+        if linkpos2 not in links[linkpos1]:
+            links[linkpos1].append(linkpos2)
+        if linkpos1 not in links[linkpos2]:
+            links[linkpos2].append(linkpos1)
+
+    # This loop starts from the `first_dum_pos` index (first dummy index)
+    # walks through the graph deleting the visited indices from `links`,
+    # it adds a gamma matrix for every free index in encounters, while it
+    # completely ignores dummy indices and virtual indices.
+    pointer = first_dum_pos
+    previous_pointer = 0
+    while True:
+        if pointer in links:
+            next_ones = links.pop(pointer)
+        else:
+            break
+
+        if previous_pointer in next_ones:
+            next_ones.remove(previous_pointer)
+
+        previous_pointer = pointer
+
+        if next_ones:
+            pointer = next_ones[0]
+        else:
+            break
+
+        if pointer == previous_pointer:
+            break
+        if pointer >=0 and free_pos[pointer] is not None:
+            for ri in resulting_indices:
+                ri.append(free_pos[pointer])
+
+    # The following loop removes the remaining connected components in `links`.
+    # If there are free indices inside a connected component, it gives a
+    # contribution to the resulting expression given by the factor
+    # `gamma_a gamma_b ... gamma_z + gamma_z ... gamma_b gamma_a`, in Kahanes's
+    # paper represented as  {gamma_a, gamma_b, ... , gamma_z},
+    # virtual indices are ignored. The variable `connected_components` is
+    # increased by one for every connected component this loop encounters.
+
+    # If the connected component has virtual and dummy indices only
+    # (no free indices), it contributes to `resulting_indices` by a factor of two.
+    # The multiplication by two is a result of the
+    # factor {gamma^0, gamma^0} = 2 I, as it appears in Kahane's paper.
+    # Note: curly brackets are meant as in the paper, as a generalized
+    # multi-element anticommutator!
+
+    while links:
+        connected_components += 1
+        pointer = min(links.keys())
+        previous_pointer = pointer
+        # the inner loop erases the visited indices from `links`, and it adds
+        # all free indices to `prepend_indices` list, virtual indices are
+        # ignored.
+        prepend_indices = []
+        while True:
+            if pointer in links:
+                next_ones = links.pop(pointer)
+            else:
+                break
+
+            if previous_pointer in next_ones:
+                if len(next_ones) > 1:
+                    next_ones.remove(previous_pointer)
+
+            previous_pointer = pointer
+
+            if next_ones:
+                pointer = next_ones[0]
+
+            if pointer >= first_dum_pos and free_pos[pointer] is not None:
+                prepend_indices.insert(0, free_pos[pointer])
+        # if `prepend_indices` is void, it means there are no free indices
+        # in the loop (and it can be shown that there must be a virtual index),
+        # loops of virtual indices only contribute by a factor of two:
+        if len(prepend_indices) == 0:
+            resulting_coeff *= 2
+        # otherwise, add the free indices in `prepend_indices` to
+        # the `resulting_indices`:
+        else:
+            expr1 = prepend_indices
+            expr2 = list(reversed(prepend_indices))
+            resulting_indices = [expri + ri for ri in resulting_indices for expri in (expr1, expr2)]
+
+    # sign correction, as described in Kahane's paper:
+    resulting_coeff *= -1 if (number_of_contractions - connected_components + 1) % 2 else 1
+    # power of two factor, as described in Kahane's paper:
+    resulting_coeff *= 2**(number_of_contractions)
+
+    # If `first_dum_pos` is not zero, it means that there are trailing free gamma
+    # matrices in front of `expression`, so multiply by them:
+    resulting_indices = [ free_pos[0:first_dum_pos] + ri for ri in resulting_indices ]
+
+    resulting_expr = S.Zero
+    for i in resulting_indices:
+        temp_expr = S.One
+        for j in i:
+            temp_expr *= GammaMatrix(j)
+        resulting_expr += temp_expr
+
+    t = resulting_coeff * resulting_expr
+    t1 = None
+    if isinstance(t, TensAdd):
+        t1 = t.args[0]
+    elif isinstance(t, TensMul):
+        t1 = t
+    if t1:
+        pass
+    else:
+        t = eye(4)*t
+    return t

venv/lib/python3.10/site-packages/sympy/physics/hep/tests/test_gamma_matrices.py

@@ -0,0 +1,427 @@
+from sympy.matrices.dense import eye, Matrix
+from sympy.tensor.tensor import tensor_indices, TensorHead, tensor_heads, \
+    TensExpr, canon_bp
+from sympy.physics.hep.gamma_matrices import GammaMatrix as G, LorentzIndex, \
+    kahane_simplify, gamma_trace, _simplify_single_line, simplify_gamma_expression
+from sympy import Symbol
+
+
+def _is_tensor_eq(arg1, arg2):
+    arg1 = canon_bp(arg1)
+    arg2 = canon_bp(arg2)
+    if isinstance(arg1, TensExpr):
+        return arg1.equals(arg2)
+    elif isinstance(arg2, TensExpr):
+        return arg2.equals(arg1)
+    return arg1 == arg2
+
+def execute_gamma_simplify_tests_for_function(tfunc, D):
+    """
+    Perform tests to check if sfunc is able to simplify gamma matrix expressions.
+
+    Parameters
+    ==========
+
+    `sfunc`     a function to simplify a `TIDS`, shall return the simplified `TIDS`.
+    `D`         the number of dimension (in most cases `D=4`).
+
+    """
+
+    mu, nu, rho, sigma = tensor_indices("mu, nu, rho, sigma", LorentzIndex)
+    a1, a2, a3, a4, a5, a6 = tensor_indices("a1:7", LorentzIndex)
+    mu11, mu12, mu21, mu31, mu32, mu41, mu51, mu52 = tensor_indices("mu11, mu12, mu21, mu31, mu32, mu41, mu51, mu52", LorentzIndex)
+    mu61, mu71, mu72 = tensor_indices("mu61, mu71, mu72", LorentzIndex)
+    m0, m1, m2, m3, m4, m5, m6 = tensor_indices("m0:7", LorentzIndex)
+
+    def g(xx, yy):
+        return (G(xx)*G(yy) + G(yy)*G(xx))/2
+
+    # Some examples taken from Kahane's paper, 4 dim only:
+    if D == 4:
+        t = (G(a1)*G(mu11)*G(a2)*G(mu21)*G(-a1)*G(mu31)*G(-a2))
+        assert _is_tensor_eq(tfunc(t), -4*G(mu11)*G(mu31)*G(mu21) - 4*G(mu31)*G(mu11)*G(mu21))
+
+        t = (G(a1)*G(mu11)*G(mu12)*\
+                              G(a2)*G(mu21)*\
+                              G(a3)*G(mu31)*G(mu32)*\
+                              G(a4)*G(mu41)*\
+                              G(-a2)*G(mu51)*G(mu52)*\
+                              G(-a1)*G(mu61)*\
+                              G(-a3)*G(mu71)*G(mu72)*\
+                              G(-a4))
+        assert _is_tensor_eq(tfunc(t), \
+            16*G(mu31)*G(mu32)*G(mu72)*G(mu71)*G(mu11)*G(mu52)*G(mu51)*G(mu12)*G(mu61)*G(mu21)*G(mu41) + 16*G(mu31)*G(mu32)*G(mu72)*G(mu71)*G(mu12)*G(mu51)*G(mu52)*G(mu11)*G(mu61)*G(mu21)*G(mu41) + 16*G(mu71)*G(mu72)*G(mu32)*G(mu31)*G(mu11)*G(mu52)*G(mu51)*G(mu12)*G(mu61)*G(mu21)*G(mu41) + 16*G(mu71)*G(mu72)*G(mu32)*G(mu31)*G(mu12)*G(mu51)*G(mu52)*G(mu11)*G(mu61)*G(mu21)*G(mu41))
+
+    # Fully Lorentz-contracted expressions, these return scalars:
+
+    def add_delta(ne):
+        return ne * eye(4)  # DiracSpinorIndex.delta(DiracSpinorIndex.auto_left, -DiracSpinorIndex.auto_right)
+
+    t = (G(mu)*G(-mu))
+    ts = add_delta(D)
+    assert _is_tensor_eq(tfunc(t), ts)
+
+    t = (G(mu)*G(nu)*G(-mu)*G(-nu))
+    ts = add_delta(2*D - D**2)  # -8
+    assert _is_tensor_eq(tfunc(t), ts)
+
+    t = (G(mu)*G(nu)*G(-nu)*G(-mu))
+    ts = add_delta(D**2)  # 16
+    assert _is_tensor_eq(tfunc(t), ts)
+
+    t = (G(mu)*G(nu)*G(-rho)*G(-nu)*G(-mu)*G(rho))
+    ts = add_delta(4*D - 4*D**2 + D**3)  # 16
+    assert _is_tensor_eq(tfunc(t), ts)
+
+    t = (G(mu)*G(nu)*G(rho)*G(-rho)*G(-nu)*G(-mu))
+    ts = add_delta(D**3)  # 64
+    assert _is_tensor_eq(tfunc(t), ts)
+
+    t = (G(a1)*G(a2)*G(a3)*G(a4)*G(-a3)*G(-a1)*G(-a2)*G(-a4))
+    ts = add_delta(-8*D + 16*D**2 - 8*D**3 + D**4)  # -32
+    assert _is_tensor_eq(tfunc(t), ts)
+
+    t = (G(-mu)*G(-nu)*G(-rho)*G(-sigma)*G(nu)*G(mu)*G(sigma)*G(rho))
+    ts = add_delta(-16*D + 24*D**2 - 8*D**3 + D**4)  # 64
+    assert _is_tensor_eq(tfunc(t), ts)
+
+    t = (G(-mu)*G(nu)*G(-rho)*G(sigma)*G(rho)*G(-nu)*G(mu)*G(-sigma))
+    ts = add_delta(8*D - 12*D**2 + 6*D**3 - D**4)  # -32
+    assert _is_tensor_eq(tfunc(t), ts)
+
+    t = (G(a1)*G(a2)*G(a3)*G(a4)*G(a5)*G(-a3)*G(-a2)*G(-a1)*G(-a5)*G(-a4))
+    ts = add_delta(64*D - 112*D**2 + 60*D**3 - 12*D**4 + D**5)  # 256
+    assert _is_tensor_eq(tfunc(t), ts)
+
+    t = (G(a1)*G(a2)*G(a3)*G(a4)*G(a5)*G(-a3)*G(-a1)*G(-a2)*G(-a4)*G(-a5))
+    ts = add_delta(64*D - 120*D**2 + 72*D**3 - 16*D**4 + D**5)  # -128
+    assert _is_tensor_eq(tfunc(t), ts)
+
+    t = (G(a1)*G(a2)*G(a3)*G(a4)*G(a5)*G(a6)*G(-a3)*G(-a2)*G(-a1)*G(-a6)*G(-a5)*G(-a4))
+    ts = add_delta(416*D - 816*D**2 + 528*D**3 - 144*D**4 + 18*D**5 - D**6)  # -128
+    assert _is_tensor_eq(tfunc(t), ts)
+
+    t = (G(a1)*G(a2)*G(a3)*G(a4)*G(a5)*G(a6)*G(-a2)*G(-a3)*G(-a1)*G(-a6)*G(-a4)*G(-a5))
+    ts = add_delta(416*D - 848*D**2 + 584*D**3 - 172*D**4 + 22*D**5 - D**6)  # -128
+    assert _is_tensor_eq(tfunc(t), ts)
+
+    # Expressions with free indices:
+
+    t = (G(mu)*G(nu)*G(rho)*G(sigma)*G(-mu))
+    assert _is_tensor_eq(tfunc(t), (-2*G(sigma)*G(rho)*G(nu) + (4-D)*G(nu)*G(rho)*G(sigma)))
+
+    t = (G(mu)*G(nu)*G(-mu))
+    assert _is_tensor_eq(tfunc(t), (2-D)*G(nu))
+
+    t = (G(mu)*G(nu)*G(rho)*G(-mu))
+    assert _is_tensor_eq(tfunc(t), 2*G(nu)*G(rho) + 2*G(rho)*G(nu) - (4-D)*G(nu)*G(rho))
+
+    t = 2*G(m2)*G(m0)*G(m1)*G(-m0)*G(-m1)
+    st = tfunc(t)
+    assert _is_tensor_eq(st, (D*(-2*D + 4))*G(m2))
+
+    t = G(m2)*G(m0)*G(m1)*G(-m0)*G(-m2)
+    st = tfunc(t)
+    assert _is_tensor_eq(st, ((-D + 2)**2)*G(m1))
+
+    t = G(m0)*G(m1)*G(m2)*G(m3)*G(-m1)
+    st = tfunc(t)
+    assert _is_tensor_eq(st, (D - 4)*G(m0)*G(m2)*G(m3) + 4*G(m0)*g(m2, m3))
+
+    t = G(m0)*G(m1)*G(m2)*G(m3)*G(-m1)*G(-m0)
+    st = tfunc(t)
+    assert _is_tensor_eq(st, ((D - 4)**2)*G(m2)*G(m3) + (8*D - 16)*g(m2, m3))
+
+    t = G(m2)*G(m0)*G(m1)*G(-m2)*G(-m0)
+    st = tfunc(t)
+    assert _is_tensor_eq(st, ((-D + 2)*(D - 4) + 4)*G(m1))
+
+    t = G(m3)*G(m1)*G(m0)*G(m2)*G(-m3)*G(-m0)*G(-m2)
+    st = tfunc(t)
+    assert _is_tensor_eq(st, (-4*D + (-D + 2)**2*(D - 4) + 8)*G(m1))
+
+    t = 2*G(m0)*G(m1)*G(m2)*G(m3)*G(-m0)
+    st = tfunc(t)
+    assert _is_tensor_eq(st, ((-2*D + 8)*G(m1)*G(m2)*G(m3) - 4*G(m3)*G(m2)*G(m1)))
+
+    t = G(m5)*G(m0)*G(m1)*G(m4)*G(m2)*G(-m4)*G(m3)*G(-m0)
+    st = tfunc(t)
+    assert _is_tensor_eq(st, (((-D + 2)*(-D + 4))*G(m5)*G(m1)*G(m2)*G(m3) + (2*D - 4)*G(m5)*G(m3)*G(m2)*G(m1)))
+
+    t = -G(m0)*G(m1)*G(m2)*G(m3)*G(-m0)*G(m4)
+    st = tfunc(t)
+    assert _is_tensor_eq(st, ((D - 4)*G(m1)*G(m2)*G(m3)*G(m4) + 2*G(m3)*G(m2)*G(m1)*G(m4)))
+
+    t = G(-m5)*G(m0)*G(m1)*G(m2)*G(m3)*G(m4)*G(-m0)*G(m5)
+    st = tfunc(t)
+
+    result1 = ((-D + 4)**2 + 4)*G(m1)*G(m2)*G(m3)*G(m4) +\
+        (4*D - 16)*G(m3)*G(m2)*G(m1)*G(m4) + (4*D - 16)*G(m4)*G(m1)*G(m2)*G(m3)\
+        + 4*G(m2)*G(m1)*G(m4)*G(m3) + 4*G(m3)*G(m4)*G(m1)*G(m2) +\
+        4*G(m4)*G(m3)*G(m2)*G(m1)
+
+    # Kahane's algorithm yields this result, which is equivalent to `result1`
+    # in four dimensions, but is not automatically recognized as equal:
+    result2 = 8*G(m1)*G(m2)*G(m3)*G(m4) + 8*G(m4)*G(m3)*G(m2)*G(m1)
+
+    if D == 4:
+        assert _is_tensor_eq(st, (result1)) or _is_tensor_eq(st, (result2))
+    else:
+        assert _is_tensor_eq(st, (result1))
+
+    # and a few very simple cases, with no contracted indices:
+
+    t = G(m0)
+    st = tfunc(t)
+    assert _is_tensor_eq(st, t)
+
+    t = -7*G(m0)
+    st = tfunc(t)
+    assert _is_tensor_eq(st, t)
+
+    t = 224*G(m0)*G(m1)*G(-m2)*G(m3)
+    st = tfunc(t)
+    assert _is_tensor_eq(st, t)
+
+
+def test_kahane_algorithm():
+    # Wrap this function to convert to and from TIDS:
+
+    def tfunc(e):
+        return _simplify_single_line(e)
+
+    execute_gamma_simplify_tests_for_function(tfunc, D=4)
+
+
+def test_kahane_simplify1():
+    i0,i1,i2,i3,i4,i5,i6,i7,i8,i9,i10,i11,i12,i13,i14,i15 = tensor_indices('i0:16', LorentzIndex)
+    mu, nu, rho, sigma = tensor_indices("mu, nu, rho, sigma", LorentzIndex)
+    D = 4
+    t = G(i0)*G(i1)
+    r = kahane_simplify(t)
+    assert r.equals(t)
+
+    t = G(i0)*G(i1)*G(-i0)
+    r = kahane_simplify(t)
+    assert r.equals(-2*G(i1))
+    t = G(i0)*G(i1)*G(-i0)
+    r = kahane_simplify(t)
+    assert r.equals(-2*G(i1))
+
+    t = G(i0)*G(i1)
+    r = kahane_simplify(t)
+    assert r.equals(t)
+    t = G(i0)*G(i1)
+    r = kahane_simplify(t)
+    assert r.equals(t)
+    t = G(i0)*G(-i0)
+    r = kahane_simplify(t)
+    assert r.equals(4*eye(4))
+    t = G(i0)*G(-i0)
+    r = kahane_simplify(t)
+    assert r.equals(4*eye(4))
+    t = G(i0)*G(-i0)
+    r = kahane_simplify(t)
+    assert r.equals(4*eye(4))
+    t = G(i0)*G(i1)*G(-i0)
+    r = kahane_simplify(t)
+    assert r.equals(-2*G(i1))
+    t = G(i0)*G(i1)*G(-i0)*G(-i1)
+    r = kahane_simplify(t)
+    assert r.equals((2*D - D**2)*eye(4))
+    t = G(i0)*G(i1)*G(-i0)*G(-i1)
+    r = kahane_simplify(t)
+    assert r.equals((2*D - D**2)*eye(4))
+    t = G(i0)*G(-i0)*G(i1)*G(-i1)
+    r = kahane_simplify(t)
+    assert r.equals(16*eye(4))
+    t = (G(mu)*G(nu)*G(-nu)*G(-mu))
+    r = kahane_simplify(t)
+    assert r.equals(D**2*eye(4))
+    t = (G(mu)*G(nu)*G(-nu)*G(-mu))
+    r = kahane_simplify(t)
+    assert r.equals(D**2*eye(4))
+    t = (G(mu)*G(nu)*G(-nu)*G(-mu))
+    r = kahane_simplify(t)
+    assert r.equals(D**2*eye(4))
+    t = (G(mu)*G(nu)*G(-rho)*G(-nu)*G(-mu)*G(rho))
+    r = kahane_simplify(t)
+    assert r.equals((4*D - 4*D**2 + D**3)*eye(4))
+    t = (G(-mu)*G(-nu)*G(-rho)*G(-sigma)*G(nu)*G(mu)*G(sigma)*G(rho))
+    r = kahane_simplify(t)
+    assert r.equals((-16*D + 24*D**2 - 8*D**3 + D**4)*eye(4))
+    t = (G(-mu)*G(nu)*G(-rho)*G(sigma)*G(rho)*G(-nu)*G(mu)*G(-sigma))
+    r = kahane_simplify(t)
+    assert r.equals((8*D - 12*D**2 + 6*D**3 - D**4)*eye(4))
+
+    # Expressions with free indices:
+    t = (G(mu)*G(nu)*G(rho)*G(sigma)*G(-mu))
+    r = kahane_simplify(t)
+    assert r.equals(-2*G(sigma)*G(rho)*G(nu))
+    t = (G(mu)*G(-mu)*G(rho)*G(sigma))
+    r = kahane_simplify(t)
+    assert r.equals(4*G(rho)*G(sigma))
+    t = (G(rho)*G(sigma)*G(mu)*G(-mu))
+    r = kahane_simplify(t)
+    assert r.equals(4*G(rho)*G(sigma))
+
+def test_gamma_matrix_class():
+    i, j, k = tensor_indices('i,j,k', LorentzIndex)
+
+    # define another type of TensorHead to see if exprs are correctly handled:
+    A = TensorHead('A', [LorentzIndex])
+
+    t = A(k)*G(i)*G(-i)
+    ts = simplify_gamma_expression(t)
+    assert _is_tensor_eq(ts, Matrix([
+        [4, 0, 0, 0],
+        [0, 4, 0, 0],
+        [0, 0, 4, 0],
+        [0, 0, 0, 4]])*A(k))
+
+    t = G(i)*A(k)*G(j)
+    ts = simplify_gamma_expression(t)
+    assert _is_tensor_eq(ts, A(k)*G(i)*G(j))
+
+    execute_gamma_simplify_tests_for_function(simplify_gamma_expression, D=4)
+
+
+def test_gamma_matrix_trace():
+    g = LorentzIndex.metric
+
+    m0, m1, m2, m3, m4, m5, m6 = tensor_indices('m0:7', LorentzIndex)
+    n0, n1, n2, n3, n4, n5 = tensor_indices('n0:6', LorentzIndex)
+
+    # working in D=4 dimensions
+    D = 4
+
+    # traces of odd number of gamma matrices are zero:
+    t = G(m0)
+    t1 = gamma_trace(t)
+    assert t1.equals(0)
+
+    t = G(m0)*G(m1)*G(m2)
+    t1 = gamma_trace(t)
+    assert t1.equals(0)
+
+    t = G(m0)*G(m1)*G(-m0)
+    t1 = gamma_trace(t)
+    assert t1.equals(0)
+
+    t = G(m0)*G(m1)*G(m2)*G(m3)*G(m4)
+    t1 = gamma_trace(t)
+    assert t1.equals(0)
+
+    # traces without internal contractions:
+    t = G(m0)*G(m1)
+    t1 = gamma_trace(t)
+    assert _is_tensor_eq(t1, 4*g(m0, m1))
+
+    t = G(m0)*G(m1)*G(m2)*G(m3)
+    t1 = gamma_trace(t)
+    t2 = -4*g(m0, m2)*g(m1, m3) + 4*g(m0, m1)*g(m2, m3) + 4*g(m0, m3)*g(m1, m2)
+    assert _is_tensor_eq(t1, t2)
+
+    t = G(m0)*G(m1)*G(m2)*G(m3)*G(m4)*G(m5)
+    t1 = gamma_trace(t)
+    t2 = t1*g(-m0, -m5)
+    t2 = t2.contract_metric(g)
+    assert _is_tensor_eq(t2, D*gamma_trace(G(m1)*G(m2)*G(m3)*G(m4)))
+
+    # traces of expressions with internal contractions:
+    t = G(m0)*G(-m0)
+    t1 = gamma_trace(t)
+    assert t1.equals(4*D)
+
+    t = G(m0)*G(m1)*G(-m0)*G(-m1)
+    t1 = gamma_trace(t)
+    assert t1.equals(8*D - 4*D**2)
+
+    t = G(m0)*G(m1)*G(m2)*G(m3)*G(m4)*G(-m0)
+    t1 = gamma_trace(t)
+    t2 = (-4*D)*g(m1, m3)*g(m2, m4) + (4*D)*g(m1, m2)*g(m3, m4) + \
+                 (4*D)*g(m1, m4)*g(m2, m3)
+    assert _is_tensor_eq(t1, t2)
+
+    t = G(-m5)*G(m0)*G(m1)*G(m2)*G(m3)*G(m4)*G(-m0)*G(m5)
+    t1 = gamma_trace(t)
+    t2 = (32*D + 4*(-D + 4)**2 - 64)*(g(m1, m2)*g(m3, m4) - \
+            g(m1, m3)*g(m2, m4) + g(m1, m4)*g(m2, m3))
+    assert _is_tensor_eq(t1, t2)
+
+    t = G(m0)*G(m1)*G(-m0)*G(m3)
+    t1 = gamma_trace(t)
+    assert t1.equals((-4*D + 8)*g(m1, m3))
+
+#    p, q = S1('p,q')
+#    ps = p(m0)*G(-m0)
+#    qs = q(m0)*G(-m0)
+#    t = ps*qs*ps*qs
+#    t1 = gamma_trace(t)
+#    assert t1 == 8*p(m0)*q(-m0)*p(m1)*q(-m1) - 4*p(m0)*p(-m0)*q(m1)*q(-m1)
+
+    t = G(m0)*G(m1)*G(m2)*G(m3)*G(m4)*G(m5)*G(-m0)*G(-m1)*G(-m2)*G(-m3)*G(-m4)*G(-m5)
+    t1 = gamma_trace(t)
+    assert t1.equals(-4*D**6 + 120*D**5 - 1040*D**4 + 3360*D**3 - 4480*D**2 + 2048*D)
+
+    t = G(m0)*G(m1)*G(n1)*G(m2)*G(n2)*G(m3)*G(m4)*G(-n2)*G(-n1)*G(-m0)*G(-m1)*G(-m2)*G(-m3)*G(-m4)
+    t1 = gamma_trace(t)
+    tresu = -7168*D + 16768*D**2 - 14400*D**3 + 5920*D**4 - 1232*D**5 + 120*D**6 - 4*D**7
+    assert t1.equals(tresu)
+
+    # checked with Mathematica
+    # In[1]:= <<Tracer.m
+    # In[2]:= Spur[l];
+    # In[3]:= GammaTrace[l, {m0},{m1},{n1},{m2},{n2},{m3},{m4},{n3},{n4},{m0},{m1},{m2},{m3},{m4}]
+    t = G(m0)*G(m1)*G(n1)*G(m2)*G(n2)*G(m3)*G(m4)*G(n3)*G(n4)*G(-m0)*G(-m1)*G(-m2)*G(-m3)*G(-m4)
+    t1 = gamma_trace(t)
+#    t1 = t1.expand_coeff()
+    c1 = -4*D**5 + 120*D**4 - 1200*D**3 + 5280*D**2 - 10560*D + 7808
+    c2 = -4*D**5 + 88*D**4 - 560*D**3 + 1440*D**2 - 1600*D + 640
+    assert _is_tensor_eq(t1, c1*g(n1, n4)*g(n2, n3) + c2*g(n1, n2)*g(n3, n4) + \
+            (-c1)*g(n1, n3)*g(n2, n4))
+
+    p, q = tensor_heads('p,q', [LorentzIndex])
+    ps = p(m0)*G(-m0)
+    qs = q(m0)*G(-m0)
+    p2 = p(m0)*p(-m0)
+    q2 = q(m0)*q(-m0)
+    pq = p(m0)*q(-m0)
+    t = ps*qs*ps*qs
+    r = gamma_trace(t)
+    assert _is_tensor_eq(r, 8*pq*pq - 4*p2*q2)
+    t = ps*qs*ps*qs*ps*qs
+    r = gamma_trace(t)
+    assert _is_tensor_eq(r, -12*p2*pq*q2 + 16*pq*pq*pq)
+    t = ps*qs*ps*qs*ps*qs*ps*qs
+    r = gamma_trace(t)
+    assert _is_tensor_eq(r, -32*pq*pq*p2*q2 + 32*pq*pq*pq*pq + 4*p2*p2*q2*q2)
+
+    t = 4*p(m1)*p(m0)*p(-m0)*q(-m1)*q(m2)*q(-m2)
+    assert _is_tensor_eq(gamma_trace(t), t)
+    t = ps*ps*ps*ps*ps*ps*ps*ps
+    r = gamma_trace(t)
+    assert r.equals(4*p2*p2*p2*p2)
+
+
+def test_bug_13636():
+    """Test issue 13636 regarding handling traces of sums of products
+    of GammaMatrix mixed with other factors."""
+    pi, ki, pf = tensor_heads("pi, ki, pf", [LorentzIndex])
+    i0, i1, i2, i3, i4 = tensor_indices("i0:5", LorentzIndex)
+    x = Symbol("x")
+    pis = pi(i2) * G(-i2)
+    kis = ki(i3) * G(-i3)
+    pfs = pf(i4) * G(-i4)
+
+    a = pfs * G(i0) * kis * G(i1) * pis * G(-i1) * kis * G(-i0)
+    b = pfs * G(i0) * kis * G(i1) * pis * x * G(-i0) * pi(-i1)
+    ta = gamma_trace(a)
+    tb = gamma_trace(b)
+    t_a_plus_b = gamma_trace(a + b)
+    assert ta == 4 * (
+        -4 * ki(i0) * ki(-i0) * pf(i1) * pi(-i1)
+        + 8 * ki(i0) * ki(i1) * pf(-i0) * pi(-i1)
+    )
+    assert tb == -8 * x * ki(i0) * pf(-i0) * pi(i1) * pi(-i1)
+    assert t_a_plus_b == ta + tb

venv/lib/python3.10/site-packages/sympy/physics/hydrogen.py

@@ -0,0 +1,265 @@
+from sympy.core.numbers import Float
+from sympy.core.singleton import S
+from sympy.functions.combinatorial.factorials import factorial
+from sympy.functions.elementary.exponential import exp
+from sympy.functions.elementary.miscellaneous import sqrt
+from sympy.functions.special.polynomials import assoc_laguerre
+from sympy.functions.special.spherical_harmonics import Ynm
+
+
+def R_nl(n, l, r, Z=1):
+    """
+    Returns the Hydrogen radial wavefunction R_{nl}.
+
+    Parameters
+    ==========
+
+    n : integer
+        Principal Quantum Number which is
+        an integer with possible values as 1, 2, 3, 4,...
+    l : integer
+        ``l`` is the Angular Momentum Quantum Number with
+        values ranging from 0 to ``n-1``.
+    r :
+        Radial coordinate.
+    Z :
+        Atomic number (1 for Hydrogen, 2 for Helium, ...)
+
+    Everything is in Hartree atomic units.
+
+    Examples
+    ========
+
+    >>> from sympy.physics.hydrogen import R_nl
+    >>> from sympy.abc import r, Z
+    >>> R_nl(1, 0, r, Z)
+    2*sqrt(Z**3)*exp(-Z*r)
+    >>> R_nl(2, 0, r, Z)
+    sqrt(2)*(-Z*r + 2)*sqrt(Z**3)*exp(-Z*r/2)/4
+    >>> R_nl(2, 1, r, Z)
+    sqrt(6)*Z*r*sqrt(Z**3)*exp(-Z*r/2)/12
+
+    For Hydrogen atom, you can just use the default value of Z=1:
+
+    >>> R_nl(1, 0, r)
+    2*exp(-r)
+    >>> R_nl(2, 0, r)
+    sqrt(2)*(2 - r)*exp(-r/2)/4
+    >>> R_nl(3, 0, r)
+    2*sqrt(3)*(2*r**2/9 - 2*r + 3)*exp(-r/3)/27
+
+    For Silver atom, you would use Z=47:
+
+    >>> R_nl(1, 0, r, Z=47)
+    94*sqrt(47)*exp(-47*r)
+    >>> R_nl(2, 0, r, Z=47)
+    47*sqrt(94)*(2 - 47*r)*exp(-47*r/2)/4
+    >>> R_nl(3, 0, r, Z=47)
+    94*sqrt(141)*(4418*r**2/9 - 94*r + 3)*exp(-47*r/3)/27
+
+    The normalization of the radial wavefunction is:
+
+    >>> from sympy import integrate, oo
+    >>> integrate(R_nl(1, 0, r)**2 * r**2, (r, 0, oo))
+    1
+    >>> integrate(R_nl(2, 0, r)**2 * r**2, (r, 0, oo))
+    1
+    >>> integrate(R_nl(2, 1, r)**2 * r**2, (r, 0, oo))
+    1
+
+    It holds for any atomic number:
+
+    >>> integrate(R_nl(1, 0, r, Z=2)**2 * r**2, (r, 0, oo))
+    1
+    >>> integrate(R_nl(2, 0, r, Z=3)**2 * r**2, (r, 0, oo))
+    1
+    >>> integrate(R_nl(2, 1, r, Z=4)**2 * r**2, (r, 0, oo))
+    1
+
+    """
+    # sympify arguments
+    n, l, r, Z = map(S, [n, l, r, Z])
+    # radial quantum number
+    n_r = n - l - 1
+    # rescaled "r"
+    a = 1/Z  # Bohr radius
+    r0 = 2 * r / (n * a)
+    # normalization coefficient
+    C = sqrt((S(2)/(n*a))**3 * factorial(n_r) / (2*n*factorial(n + l)))
+    # This is an equivalent normalization coefficient, that can be found in
+    # some books. Both coefficients seem to be the same fast:
+    # C =  S(2)/n**2 * sqrt(1/a**3 * factorial(n_r) / (factorial(n+l)))
+    return C * r0**l * assoc_laguerre(n_r, 2*l + 1, r0).expand() * exp(-r0/2)
+
+
+def Psi_nlm(n, l, m, r, phi, theta, Z=1):
+    """
+    Returns the Hydrogen wave function psi_{nlm}. It's the product of
+    the radial wavefunction R_{nl} and the spherical harmonic Y_{l}^{m}.
+
+    Parameters
+    ==========
+
+    n : integer
+        Principal Quantum Number which is
+        an integer with possible values as 1, 2, 3, 4,...
+    l : integer
+        ``l`` is the Angular Momentum Quantum Number with
+        values ranging from 0 to ``n-1``.
+    m : integer
+        ``m`` is the Magnetic Quantum Number with values
+        ranging from ``-l`` to ``l``.
+    r :
+        radial coordinate
+    phi :
+        azimuthal angle
+    theta :
+        polar angle
+    Z :
+        atomic number (1 for Hydrogen, 2 for Helium, ...)
+
+    Everything is in Hartree atomic units.
+
+    Examples
+    ========
+
+    >>> from sympy.physics.hydrogen import Psi_nlm
+    >>> from sympy import Symbol
+    >>> r=Symbol("r", positive=True)
+    >>> phi=Symbol("phi", real=True)
+    >>> theta=Symbol("theta", real=True)
+    >>> Z=Symbol("Z", positive=True, integer=True, nonzero=True)
+    >>> Psi_nlm(1,0,0,r,phi,theta,Z)
+    Z**(3/2)*exp(-Z*r)/sqrt(pi)
+    >>> Psi_nlm(2,1,1,r,phi,theta,Z)
+    -Z**(5/2)*r*exp(I*phi)*exp(-Z*r/2)*sin(theta)/(8*sqrt(pi))
+
+    Integrating the absolute square of a hydrogen wavefunction psi_{nlm}
+    over the whole space leads 1.
+
+    The normalization of the hydrogen wavefunctions Psi_nlm is:
+
+    >>> from sympy import integrate, conjugate, pi, oo, sin
+    >>> wf=Psi_nlm(2,1,1,r,phi,theta,Z)
+    >>> abs_sqrd=wf*conjugate(wf)
+    >>> jacobi=r**2*sin(theta)
+    >>> integrate(abs_sqrd*jacobi, (r,0,oo), (phi,0,2*pi), (theta,0,pi))
+    1
+    """
+
+    # sympify arguments
+    n, l, m, r, phi, theta, Z = map(S, [n, l, m, r, phi, theta, Z])
+    # check if values for n,l,m make physically sense
+    if n.is_integer and n < 1:
+        raise ValueError("'n' must be positive integer")
+    if l.is_integer and not (n > l):
+        raise ValueError("'n' must be greater than 'l'")
+    if m.is_integer and not (abs(m) <= l):
+        raise ValueError("|'m'| must be less or equal 'l'")
+    # return the hydrogen wave function
+    return R_nl(n, l, r, Z)*Ynm(l, m, theta, phi).expand(func=True)
+
+
+def E_nl(n, Z=1):
+    """
+    Returns the energy of the state (n, l) in Hartree atomic units.
+
+    The energy does not depend on "l".
+
+    Parameters
+    ==========
+
+    n : integer
+        Principal Quantum Number which is
+        an integer with possible values as 1, 2, 3, 4,...
+    Z :
+        Atomic number (1 for Hydrogen, 2 for Helium, ...)
+
+    Examples
+    ========
+
+    >>> from sympy.physics.hydrogen import E_nl
+    >>> from sympy.abc import n, Z
+    >>> E_nl(n, Z)
+    -Z**2/(2*n**2)
+    >>> E_nl(1)
+    -1/2
+    >>> E_nl(2)
+    -1/8
+    >>> E_nl(3)
+    -1/18
+    >>> E_nl(3, 47)
+    -2209/18
+
+    """
+    n, Z = S(n), S(Z)
+    if n.is_integer and (n < 1):
+        raise ValueError("'n' must be positive integer")
+    return -Z**2/(2*n**2)
+
+
+def E_nl_dirac(n, l, spin_up=True, Z=1, c=Float("137.035999037")):
+    """
+    Returns the relativistic energy of the state (n, l, spin) in Hartree atomic
+    units.
+
+    The energy is calculated from the Dirac equation. The rest mass energy is
+    *not* included.
+
+    Parameters
+    ==========
+
+    n : integer
+        Principal Quantum Number which is
+        an integer with possible values as 1, 2, 3, 4,...
+    l : integer
+        ``l`` is the Angular Momentum Quantum Number with
+        values ranging from 0 to ``n-1``.
+    spin_up :
+        True if the electron spin is up (default), otherwise down
+    Z :
+        Atomic number (1 for Hydrogen, 2 for Helium, ...)
+    c :
+        Speed of light in atomic units. Default value is 137.035999037,
+        taken from https://arxiv.org/abs/1012.3627
+
+    Examples
+    ========
+
+    >>> from sympy.physics.hydrogen import E_nl_dirac
+    >>> E_nl_dirac(1, 0)
+    -0.500006656595360
+
+    >>> E_nl_dirac(2, 0)
+    -0.125002080189006
+    >>> E_nl_dirac(2, 1)
+    -0.125000416028342
+    >>> E_nl_dirac(2, 1, False)
+    -0.125002080189006
+
+    >>> E_nl_dirac(3, 0)
+    -0.0555562951740285
+    >>> E_nl_dirac(3, 1)
+    -0.0555558020932949
+    >>> E_nl_dirac(3, 1, False)
+    -0.0555562951740285
+    >>> E_nl_dirac(3, 2)
+    -0.0555556377366884
+    >>> E_nl_dirac(3, 2, False)
+    -0.0555558020932949
+
+    """
+    n, l, Z, c = map(S, [n, l, Z, c])
+    if not (l >= 0):
+        raise ValueError("'l' must be positive or zero")
+    if not (n > l):
+        raise ValueError("'n' must be greater than 'l'")
+    if (l == 0 and spin_up is False):
+        raise ValueError("Spin must be up for l==0.")
+    # skappa is sign*kappa, where sign contains the correct sign
+    if spin_up:
+        skappa = -l - 1
+    else:
+        skappa = -l
+    beta = sqrt(skappa**2 - Z**2/c**2)
+    return c**2/sqrt(1 + Z**2/(n + skappa + beta)**2/c**2) - c**2

venv/lib/python3.10/site-packages/sympy/physics/matrices.py

@@ -0,0 +1,176 @@
+"""Known matrices related to physics"""
+
+from sympy.core.numbers import I
+from sympy.matrices.dense import MutableDenseMatrix as Matrix
+from sympy.utilities.decorator import deprecated
+
+
+def msigma(i):
+    r"""Returns a Pauli matrix `\sigma_i` with `i=1,2,3`.
+
+    References
+    ==========
+
+    .. [1] https://en.wikipedia.org/wiki/Pauli_matrices
+
+    Examples
+    ========
+
+    >>> from sympy.physics.matrices import msigma
+    >>> msigma(1)
+    Matrix([
+    [0, 1],
+    [1, 0]])
+    """
+    if i == 1:
+        mat = (
+            (0, 1),
+            (1, 0)
+        )
+    elif i == 2:
+        mat = (
+            (0, -I),
+            (I, 0)
+        )
+    elif i == 3:
+        mat = (
+            (1, 0),
+            (0, -1)
+        )
+    else:
+        raise IndexError("Invalid Pauli index")
+    return Matrix(mat)
+
+
+def pat_matrix(m, dx, dy, dz):
+    """Returns the Parallel Axis Theorem matrix to translate the inertia
+    matrix a distance of `(dx, dy, dz)` for a body of mass m.
+
+    Examples
+    ========
+
+    To translate a body having a mass of 2 units a distance of 1 unit along
+    the `x`-axis we get:
+
+    >>> from sympy.physics.matrices import pat_matrix
+    >>> pat_matrix(2, 1, 0, 0)
+    Matrix([
+    [0, 0, 0],
+    [0, 2, 0],
+    [0, 0, 2]])
+
+    """
+    dxdy = -dx*dy
+    dydz = -dy*dz
+    dzdx = -dz*dx
+    dxdx = dx**2
+    dydy = dy**2
+    dzdz = dz**2
+    mat = ((dydy + dzdz, dxdy, dzdx),
+           (dxdy, dxdx + dzdz, dydz),
+           (dzdx, dydz, dydy + dxdx))
+    return m*Matrix(mat)
+
+
+def mgamma(mu, lower=False):
+    r"""Returns a Dirac gamma matrix `\gamma^\mu` in the standard
+    (Dirac) representation.
+
+    Explanation
+    ===========
+
+    If you want `\gamma_\mu`, use ``gamma(mu, True)``.
+
+    We use a convention:
+
+    `\gamma^5 = i \cdot \gamma^0 \cdot \gamma^1 \cdot \gamma^2 \cdot \gamma^3`
+
+    `\gamma_5 = i \cdot \gamma_0 \cdot \gamma_1 \cdot \gamma_2 \cdot \gamma_3 = - \gamma^5`
+
+    References
+    ==========
+
+    .. [1] https://en.wikipedia.org/wiki/Gamma_matrices
+
+    Examples
+    ========
+
+    >>> from sympy.physics.matrices import mgamma
+    >>> mgamma(1)
+    Matrix([
+    [ 0,  0, 0, 1],
+    [ 0,  0, 1, 0],
+    [ 0, -1, 0, 0],
+    [-1,  0, 0, 0]])
+    """
+    if mu not in (0, 1, 2, 3, 5):
+        raise IndexError("Invalid Dirac index")
+    if mu == 0:
+        mat = (
+            (1, 0, 0, 0),
+            (0, 1, 0, 0),
+            (0, 0, -1, 0),
+            (0, 0, 0, -1)
+        )
+    elif mu == 1:
+        mat = (
+            (0, 0, 0, 1),
+            (0, 0, 1, 0),
+            (0, -1, 0, 0),
+            (-1, 0, 0, 0)
+        )
+    elif mu == 2:
+        mat = (
+            (0, 0, 0, -I),
+            (0, 0, I, 0),
+            (0, I, 0, 0),
+            (-I, 0, 0, 0)
+        )
+    elif mu == 3:
+        mat = (
+            (0, 0, 1, 0),
+            (0, 0, 0, -1),
+            (-1, 0, 0, 0),
+            (0, 1, 0, 0)
+        )
+    elif mu == 5:
+        mat = (
+            (0, 0, 1, 0),
+            (0, 0, 0, 1),
+            (1, 0, 0, 0),
+            (0, 1, 0, 0)
+        )
+    m = Matrix(mat)
+    if lower:
+        if mu in (1, 2, 3, 5):
+            m = -m
+    return m
+
+#Minkowski tensor using the convention (+,-,-,-) used in the Quantum Field
+#Theory
+minkowski_tensor = Matrix( (
+    (1, 0, 0, 0),
+    (0, -1, 0, 0),
+    (0, 0, -1, 0),
+    (0, 0, 0, -1)
+))
+
+
+@deprecated(
+    """
+    The sympy.physics.matrices.mdft method is deprecated. Use
+    sympy.DFT(n).as_explicit() instead.
+    """,
+    deprecated_since_version="1.9",
+    active_deprecations_target="deprecated-physics-mdft",
+)
+def mdft(n):
+    r"""
+    .. deprecated:: 1.9
+
+       Use DFT from sympy.matrices.expressions.fourier instead.
+
+       To get identical behavior to ``mdft(n)``, use ``DFT(n).as_explicit()``.
+    """
+    from sympy.matrices.expressions.fourier import DFT
+    return DFT(n).as_mutable()

venv/lib/python3.10/site-packages/sympy/physics/mechanics/__init__.py

@@ -0,0 +1,66 @@
+__all__ = [
+    'vector',
+
+    'CoordinateSym', 'ReferenceFrame', 'Dyadic', 'Vector', 'Point', 'cross',
+    'dot', 'express', 'time_derivative', 'outer', 'kinematic_equations',
+    'get_motion_params', 'partial_velocity', 'dynamicsymbols', 'vprint',
+    'vsstrrepr', 'vsprint', 'vpprint', 'vlatex', 'init_vprinting', 'curl',
+    'divergence', 'gradient', 'is_conservative', 'is_solenoidal',
+    'scalar_potential', 'scalar_potential_difference',
+
+    'KanesMethod',
+
+    'RigidBody',
+
+    'inertia', 'inertia_of_point_mass', 'linear_momentum', 'angular_momentum',
+    'kinetic_energy', 'potential_energy', 'Lagrangian', 'mechanics_printing',
+    'mprint', 'msprint', 'mpprint', 'mlatex', 'msubs', 'find_dynamicsymbols',
+
+    'Particle',
+
+    'LagrangesMethod',
+
+    'Linearizer',
+
+    'Body',
+
+    'SymbolicSystem',
+
+    'PinJoint', 'PrismaticJoint', 'CylindricalJoint', 'PlanarJoint',
+    'SphericalJoint', 'WeldJoint',
+
+    'JointsMethod'
+]
+
+from sympy.physics import vector
+
+from sympy.physics.vector import (CoordinateSym, ReferenceFrame, Dyadic, Vector, Point,
+        cross, dot, express, time_derivative, outer, kinematic_equations,
+        get_motion_params, partial_velocity, dynamicsymbols, vprint,
+        vsstrrepr, vsprint, vpprint, vlatex, init_vprinting, curl, divergence,
+        gradient, is_conservative, is_solenoidal, scalar_potential,
+        scalar_potential_difference)
+
+from .kane import KanesMethod
+
+from .rigidbody import RigidBody
+
+from .functions import (inertia, inertia_of_point_mass, linear_momentum,
+        angular_momentum, kinetic_energy, potential_energy, Lagrangian,
+        mechanics_printing, mprint, msprint, mpprint, mlatex, msubs,
+        find_dynamicsymbols)
+
+from .particle import Particle
+
+from .lagrange import LagrangesMethod
+
+from .linearize import Linearizer
+
+from .body import Body
+
+from .system import SymbolicSystem
+
+from .jointsmethod import JointsMethod
+
+from .joint import (PinJoint, PrismaticJoint, CylindricalJoint, PlanarJoint,
+                    SphericalJoint, WeldJoint)

venv/lib/python3.10/site-packages/sympy/physics/mechanics/body.py

@@ -0,0 +1,611 @@
+from sympy.core.backend import Symbol
+from sympy.physics.vector import Point, Vector, ReferenceFrame, Dyadic
+from sympy.physics.mechanics import RigidBody, Particle, inertia
+
+__all__ = ['Body']
+
+
+# XXX: We use type:ignore because the classes RigidBody and Particle have
+# inconsistent parallel axis methods that take different numbers of arguments.
+class Body(RigidBody, Particle):  # type: ignore
+    """
+    Body is a common representation of either a RigidBody or a Particle SymPy
+    object depending on what is passed in during initialization. If a mass is
+    passed in and central_inertia is left as None, the Particle object is
+    created. Otherwise a RigidBody object will be created.
+
+    Explanation
+    ===========
+
+    The attributes that Body possesses will be the same as a Particle instance
+    or a Rigid Body instance depending on which was created. Additional
+    attributes are listed below.
+
+    Attributes
+    ==========
+
+    name : string
+        The body's name
+    masscenter : Point
+        The point which represents the center of mass of the rigid body
+    frame : ReferenceFrame
+        The reference frame which the body is fixed in
+    mass : Sympifyable
+        The body's mass
+    inertia : (Dyadic, Point)
+        The body's inertia around its center of mass. This attribute is specific
+        to the rigid body form of Body and is left undefined for the Particle
+        form
+    loads : iterable
+        This list contains information on the different loads acting on the
+        Body. Forces are listed as a (point, vector) tuple and torques are
+        listed as (reference frame, vector) tuples.
+
+    Parameters
+    ==========
+
+    name : String
+        Defines the name of the body. It is used as the base for defining
+        body specific properties.
+    masscenter : Point, optional
+        A point that represents the center of mass of the body or particle.
+        If no point is given, a point is generated.
+    mass : Sympifyable, optional
+        A Sympifyable object which represents the mass of the body. If no
+        mass is passed, one is generated.
+    frame : ReferenceFrame, optional
+        The ReferenceFrame that represents the reference frame of the body.
+        If no frame is given, a frame is generated.
+    central_inertia : Dyadic, optional
+        Central inertia dyadic of the body. If none is passed while creating
+        RigidBody, a default inertia is generated.
+
+    Examples
+    ========
+
+    Default behaviour. This results in the creation of a RigidBody object for
+    which the mass, mass center, frame and inertia attributes are given default
+    values. ::
+
+        >>> from sympy.physics.mechanics import Body
+        >>> body = Body('name_of_body')
+
+    This next example demonstrates the code required to specify all of the
+    values of the Body object. Note this will also create a RigidBody version of
+    the Body object. ::
+
+        >>> from sympy import Symbol
+        >>> from sympy.physics.mechanics import ReferenceFrame, Point, inertia
+        >>> from sympy.physics.mechanics import Body
+        >>> mass = Symbol('mass')
+        >>> masscenter = Point('masscenter')
+        >>> frame = ReferenceFrame('frame')
+        >>> ixx = Symbol('ixx')
+        >>> body_inertia = inertia(frame, ixx, 0, 0)
+        >>> body = Body('name_of_body', masscenter, mass, frame, body_inertia)
+
+    The minimal code required to create a Particle version of the Body object
+    involves simply passing in a name and a mass. ::
+
+        >>> from sympy import Symbol
+        >>> from sympy.physics.mechanics import Body
+        >>> mass = Symbol('mass')
+        >>> body = Body('name_of_body', mass=mass)
+
+    The Particle version of the Body object can also receive a masscenter point
+    and a reference frame, just not an inertia.
+    """
+
+    def __init__(self, name, masscenter=None, mass=None, frame=None,
+                 central_inertia=None):
+
+        self.name = name
+        self._loads = []
+
+        if frame is None:
+            frame = ReferenceFrame(name + '_frame')
+
+        if masscenter is None:
+            masscenter = Point(name + '_masscenter')
+
+        if central_inertia is None and mass is None:
+            ixx = Symbol(name + '_ixx')
+            iyy = Symbol(name + '_iyy')
+            izz = Symbol(name + '_izz')
+            izx = Symbol(name + '_izx')
+            ixy = Symbol(name + '_ixy')
+            iyz = Symbol(name + '_iyz')
+            _inertia = (inertia(frame, ixx, iyy, izz, ixy, iyz, izx),
+                        masscenter)
+        else:
+            _inertia = (central_inertia, masscenter)
+
+        if mass is None:
+            _mass = Symbol(name + '_mass')
+        else:
+            _mass = mass
+
+        masscenter.set_vel(frame, 0)
+
+        # If user passes masscenter and mass then a particle is created
+        # otherwise a rigidbody. As a result a body may or may not have inertia.
+        if central_inertia is None and mass is not None:
+            self.frame = frame
+            self.masscenter = masscenter
+            Particle.__init__(self, name, masscenter, _mass)
+            self._central_inertia = Dyadic(0)
+        else:
+            RigidBody.__init__(self, name, masscenter, frame, _mass, _inertia)
+
+    @property
+    def loads(self):
+        return self._loads
+
+    @property
+    def x(self):
+        """The basis Vector for the Body, in the x direction."""
+        return self.frame.x
+
+    @property
+    def y(self):
+        """The basis Vector for the Body, in the y direction."""
+        return self.frame.y
+
+    @property
+    def z(self):
+        """The basis Vector for the Body, in the z direction."""
+        return self.frame.z
+
+    @property
+    def inertia(self):
+        """The body's inertia about a point; stored as (Dyadic, Point)."""
+        if self.is_rigidbody:
+            return RigidBody.inertia.fget(self)
+        return (self.central_inertia, self.masscenter)
+
+    @inertia.setter
+    def inertia(self, I):
+        RigidBody.inertia.fset(self, I)
+
+    @property
+    def is_rigidbody(self):
+        if hasattr(self, '_inertia'):
+            return True
+        return False
+
+    def kinetic_energy(self, frame):
+        """Kinetic energy of the body.
+
+        Parameters
+        ==========
+
+        frame : ReferenceFrame or Body
+            The Body's angular velocity and the velocity of it's mass
+            center are typically defined with respect to an inertial frame but
+            any relevant frame in which the velocities are known can be supplied.
+
+        Examples
+        ========
+
+        >>> from sympy.physics.mechanics import Body, ReferenceFrame, Point
+        >>> from sympy import symbols
+        >>> m, v, r, omega = symbols('m v r omega')
+        >>> N = ReferenceFrame('N')
+        >>> O = Point('O')
+        >>> P = Body('P', masscenter=O, mass=m)
+        >>> P.masscenter.set_vel(N, v * N.y)
+        >>> P.kinetic_energy(N)
+        m*v**2/2
+
+        >>> N = ReferenceFrame('N')
+        >>> b = ReferenceFrame('b')
+        >>> b.set_ang_vel(N, omega * b.x)
+        >>> P = Point('P')
+        >>> P.set_vel(N, v * N.x)
+        >>> B = Body('B', masscenter=P, frame=b)
+        >>> B.kinetic_energy(N)
+        B_ixx*omega**2/2 + B_mass*v**2/2
+
+        See Also
+        ========
+
+        sympy.physics.mechanics : Particle, RigidBody
+
+        """
+        if isinstance(frame, Body):
+            frame = Body.frame
+        if self.is_rigidbody:
+            return RigidBody(self.name, self.masscenter, self.frame, self.mass,
+                            (self.central_inertia, self.masscenter)).kinetic_energy(frame)
+        return Particle(self.name, self.masscenter, self.mass).kinetic_energy(frame)
+
+    def apply_force(self, force, point=None, reaction_body=None, reaction_point=None):
+        """Add force to the body(s).
+
+        Explanation
+        ===========
+
+        Applies the force on self or equal and oppposite forces on
+        self and other body if both are given on the desried point on the bodies.
+        The force applied on other body is taken opposite of self, i.e, -force.
+
+        Parameters
+        ==========
+
+        force: Vector
+            The force to be applied.
+        point: Point, optional
+            The point on self on which force is applied.
+            By default self's masscenter.
+        reaction_body: Body, optional
+            Second body on which equal and opposite force
+            is to be applied.
+        reaction_point : Point, optional
+            The point on other body on which equal and opposite
+            force is applied. By default masscenter of other body.
+
+        Example
+        =======
+
+        >>> from sympy import symbols
+        >>> from sympy.physics.mechanics import Body, Point, dynamicsymbols
+        >>> m, g = symbols('m g')
+        >>> B = Body('B')
+        >>> force1 = m*g*B.z
+        >>> B.apply_force(force1) #Applying force on B's masscenter
+        >>> B.loads
+        [(B_masscenter, g*m*B_frame.z)]
+
+        We can also remove some part of force from any point on the body by
+        adding the opposite force to the body on that point.
+
+        >>> f1, f2 = dynamicsymbols('f1 f2')
+        >>> P = Point('P') #Considering point P on body B
+        >>> B.apply_force(f1*B.x + f2*B.y, P)
+        >>> B.loads
+        [(B_masscenter, g*m*B_frame.z), (P, f1(t)*B_frame.x + f2(t)*B_frame.y)]
+
+        Let's remove f1 from point P on body B.
+
+        >>> B.apply_force(-f1*B.x, P)
+        >>> B.loads
+        [(B_masscenter, g*m*B_frame.z), (P, f2(t)*B_frame.y)]
+
+        To further demonstrate the use of ``apply_force`` attribute,
+        consider two bodies connected through a spring.
+
+        >>> from sympy.physics.mechanics import Body, dynamicsymbols
+        >>> N = Body('N') #Newtonion Frame
+        >>> x = dynamicsymbols('x')
+        >>> B1 = Body('B1')
+        >>> B2 = Body('B2')
+        >>> spring_force = x*N.x
+
+        Now let's apply equal and opposite spring force to the bodies.
+
+        >>> P1 = Point('P1')
+        >>> P2 = Point('P2')
+        >>> B1.apply_force(spring_force, point=P1, reaction_body=B2, reaction_point=P2)
+
+        We can check the loads(forces) applied to bodies now.
+
+        >>> B1.loads
+        [(P1, x(t)*N_frame.x)]
+        >>> B2.loads
+        [(P2, - x(t)*N_frame.x)]
+
+        Notes
+        =====
+
+        If a new force is applied to a body on a point which already has some
+        force applied on it, then the new force is added to the already applied
+        force on that point.
+
+        """
+
+        if not isinstance(point, Point):
+            if point is None:
+                point = self.masscenter  # masscenter
+            else:
+                raise TypeError("Force must be applied to a point on the body.")
+        if not isinstance(force, Vector):
+            raise TypeError("Force must be a vector.")
+
+        if reaction_body is not None:
+            reaction_body.apply_force(-force, point=reaction_point)
+
+        for load in self._loads:
+            if point in load:
+                force += load[1]
+                self._loads.remove(load)
+                break
+
+        self._loads.append((point, force))
+
+    def apply_torque(self, torque, reaction_body=None):
+        """Add torque to the body(s).
+
+        Explanation
+        ===========
+
+        Applies the torque on self or equal and oppposite torquess on
+        self and other body if both are given.
+        The torque applied on other body is taken opposite of self,
+        i.e, -torque.
+
+        Parameters
+        ==========
+
+        torque: Vector
+            The torque to be applied.
+        reaction_body: Body, optional
+            Second body on which equal and opposite torque
+            is to be applied.
+
+        Example
+        =======
+
+        >>> from sympy import symbols
+        >>> from sympy.physics.mechanics import Body, dynamicsymbols
+        >>> t = symbols('t')
+        >>> B = Body('B')
+        >>> torque1 = t*B.z
+        >>> B.apply_torque(torque1)
+        >>> B.loads
+        [(B_frame, t*B_frame.z)]
+
+        We can also remove some part of torque from the body by
+        adding the opposite torque to the body.
+
+        >>> t1, t2 = dynamicsymbols('t1 t2')
+        >>> B.apply_torque(t1*B.x + t2*B.y)
+        >>> B.loads
+        [(B_frame, t1(t)*B_frame.x + t2(t)*B_frame.y + t*B_frame.z)]
+
+        Let's remove t1 from Body B.
+
+        >>> B.apply_torque(-t1*B.x)
+        >>> B.loads
+        [(B_frame, t2(t)*B_frame.y + t*B_frame.z)]
+
+        To further demonstrate the use, let us consider two bodies such that
+        a torque `T` is acting on one body, and `-T` on the other.
+
+        >>> from sympy.physics.mechanics import Body, dynamicsymbols
+        >>> N = Body('N') #Newtonion frame
+        >>> B1 = Body('B1')
+        >>> B2 = Body('B2')
+        >>> v = dynamicsymbols('v')
+        >>> T = v*N.y #Torque
+
+        Now let's apply equal and opposite torque to the bodies.
+
+        >>> B1.apply_torque(T, B2)
+
+        We can check the loads (torques) applied to bodies now.
+
+        >>> B1.loads
+        [(B1_frame, v(t)*N_frame.y)]
+        >>> B2.loads
+        [(B2_frame, - v(t)*N_frame.y)]
+
+        Notes
+        =====
+
+        If a new torque is applied on body which already has some torque applied on it,
+        then the new torque is added to the previous torque about the body's frame.
+
+        """
+
+        if not isinstance(torque, Vector):
+            raise TypeError("A Vector must be supplied to add torque.")
+
+        if reaction_body is not None:
+            reaction_body.apply_torque(-torque)
+
+        for load in self._loads:
+            if self.frame in load:
+                torque += load[1]
+                self._loads.remove(load)
+                break
+        self._loads.append((self.frame, torque))
+
+    def clear_loads(self):
+        """
+        Clears the Body's loads list.
+
+        Example
+        =======
+
+        >>> from sympy.physics.mechanics import Body
+        >>> B = Body('B')
+        >>> force = B.x + B.y
+        >>> B.apply_force(force)
+        >>> B.loads
+        [(B_masscenter, B_frame.x + B_frame.y)]
+        >>> B.clear_loads()
+        >>> B.loads
+        []
+
+        """
+
+        self._loads = []
+
+    def remove_load(self, about=None):
+        """
+        Remove load about a point or frame.
+
+        Parameters
+        ==========
+
+        about : Point or ReferenceFrame, optional
+            The point about which force is applied,
+            and is to be removed.
+            If about is None, then the torque about
+            self's frame is removed.
+
+        Example
+        =======
+
+        >>> from sympy.physics.mechanics import Body, Point
+        >>> B = Body('B')
+        >>> P = Point('P')
+        >>> f1 = B.x
+        >>> f2 = B.y
+        >>> B.apply_force(f1)
+        >>> B.apply_force(f2, P)
+        >>> B.loads
+        [(B_masscenter, B_frame.x), (P, B_frame.y)]
+
+        >>> B.remove_load(P)
+        >>> B.loads
+        [(B_masscenter, B_frame.x)]
+
+        """
+
+        if about is not None:
+            if not isinstance(about, Point):
+                raise TypeError('Load is applied about Point or ReferenceFrame.')
+        else:
+            about = self.frame
+
+        for load in self._loads:
+            if about in load:
+                self._loads.remove(load)
+                break
+
+    def masscenter_vel(self, body):
+        """
+        Returns the velocity of the mass center with respect to the provided
+        rigid body or reference frame.
+
+        Parameters
+        ==========
+
+        body: Body or ReferenceFrame
+            The rigid body or reference frame to calculate the velocity in.
+
+        Example
+        =======
+
+        >>> from sympy.physics.mechanics import Body
+        >>> A = Body('A')
+        >>> B = Body('B')
+        >>> A.masscenter.set_vel(B.frame, 5*B.frame.x)
+        >>> A.masscenter_vel(B)
+        5*B_frame.x
+        >>> A.masscenter_vel(B.frame)
+        5*B_frame.x
+
+        """
+
+        if isinstance(body,  ReferenceFrame):
+            frame=body
+        elif isinstance(body, Body):
+            frame = body.frame
+        return self.masscenter.vel(frame)
+
+    def ang_vel_in(self, body):
+        """
+        Returns this body's angular velocity with respect to the provided
+        rigid body or reference frame.
+
+        Parameters
+        ==========
+
+        body: Body or ReferenceFrame
+            The rigid body or reference frame to calculate the angular velocity in.
+
+        Example
+        =======
+
+        >>> from sympy.physics.mechanics import Body, ReferenceFrame
+        >>> A = Body('A')
+        >>> N = ReferenceFrame('N')
+        >>> B = Body('B', frame=N)
+        >>> A.frame.set_ang_vel(N, 5*N.x)
+        >>> A.ang_vel_in(B)
+        5*N.x
+        >>> A.ang_vel_in(N)
+        5*N.x
+
+        """
+
+        if isinstance(body,  ReferenceFrame):
+            frame=body
+        elif isinstance(body, Body):
+            frame = body.frame
+        return self.frame.ang_vel_in(frame)
+
+    def dcm(self, body):
+        """
+        Returns the direction cosine matrix of this body relative to the
+        provided rigid body or reference frame.
+
+        Parameters
+        ==========
+
+        body: Body or ReferenceFrame
+            The rigid body or reference frame to calculate the dcm.
+
+        Example
+        =======
+
+        >>> from sympy.physics.mechanics import Body
+        >>> A = Body('A')
+        >>> B = Body('B')
+        >>> A.frame.orient_axis(B.frame, B.frame.x, 5)
+        >>> A.dcm(B)
+        Matrix([
+        [1,       0,      0],
+        [0,  cos(5), sin(5)],
+        [0, -sin(5), cos(5)]])
+        >>> A.dcm(B.frame)
+        Matrix([
+        [1,       0,      0],
+        [0,  cos(5), sin(5)],
+        [0, -sin(5), cos(5)]])
+
+        """
+
+        if isinstance(body,  ReferenceFrame):
+            frame=body
+        elif isinstance(body, Body):
+            frame = body.frame
+        return self.frame.dcm(frame)
+
+    def parallel_axis(self, point, frame=None):
+        """Returns the inertia dyadic of the body with respect to another
+        point.
+
+        Parameters
+        ==========
+
+        point : sympy.physics.vector.Point
+            The point to express the inertia dyadic about.
+        frame : sympy.physics.vector.ReferenceFrame
+            The reference frame used to construct the dyadic.
+
+        Returns
+        =======
+
+        inertia : sympy.physics.vector.Dyadic
+            The inertia dyadic of the rigid body expressed about the provided
+            point.
+
+        Example
+        =======
+
+        >>> from sympy.physics.mechanics import Body
+        >>> A = Body('A')
+        >>> P = A.masscenter.locatenew('point', 3 * A.x + 5 * A.y)
+        >>> A.parallel_axis(P).to_matrix(A.frame)
+        Matrix([
+        [A_ixx + 25*A_mass, A_ixy - 15*A_mass,             A_izx],
+        [A_ixy - 15*A_mass,  A_iyy + 9*A_mass,             A_iyz],
+        [            A_izx,             A_iyz, A_izz + 34*A_mass]])
+
+        """
+        if self.is_rigidbody:
+            return RigidBody.parallel_axis(self, point, frame)
+        return Particle.parallel_axis(self, point, frame)

venv/lib/python3.10/site-packages/sympy/physics/mechanics/functions.py

@@ -0,0 +1,779 @@
+from sympy.utilities import dict_merge
+from sympy.utilities.iterables import iterable
+from sympy.physics.vector import (Dyadic, Vector, ReferenceFrame,
+                                  Point, dynamicsymbols)
+from sympy.physics.vector.printing import (vprint, vsprint, vpprint, vlatex,
+                                           init_vprinting)
+from sympy.physics.mechanics.particle import Particle
+from sympy.physics.mechanics.rigidbody import RigidBody
+from sympy.simplify.simplify import simplify
+from sympy.core.backend import (Matrix, sympify, Mul, Derivative, sin, cos,
+                                tan, AppliedUndef, S)
+
+__all__ = ['inertia',
+           'inertia_of_point_mass',
+           'linear_momentum',
+           'angular_momentum',
+           'kinetic_energy',
+           'potential_energy',
+           'Lagrangian',
+           'mechanics_printing',
+           'mprint',
+           'msprint',
+           'mpprint',
+           'mlatex',
+           'msubs',
+           'find_dynamicsymbols']
+
+# These are functions that we've moved and renamed during extracting the
+# basic vector calculus code from the mechanics packages.
+
+mprint = vprint
+msprint = vsprint
+mpprint = vpprint
+mlatex = vlatex
+
+
+def mechanics_printing(**kwargs):
+    """
+    Initializes time derivative printing for all SymPy objects in
+    mechanics module.
+    """
+
+    init_vprinting(**kwargs)
+
+mechanics_printing.__doc__ = init_vprinting.__doc__
+
+
+def inertia(frame, ixx, iyy, izz, ixy=0, iyz=0, izx=0):
+    """Simple way to create inertia Dyadic object.
+
+    Explanation
+    ===========
+
+    If you do not know what a Dyadic is, just treat this like the inertia
+    tensor. Then, do the easy thing and define it in a body-fixed frame.
+
+    Parameters
+    ==========
+
+    frame : ReferenceFrame
+        The frame the inertia is defined in
+    ixx : Sympifyable
+        the xx element in the inertia dyadic
+    iyy : Sympifyable
+        the yy element in the inertia dyadic
+    izz : Sympifyable
+        the zz element in the inertia dyadic
+    ixy : Sympifyable
+        the xy element in the inertia dyadic
+    iyz : Sympifyable
+        the yz element in the inertia dyadic
+    izx : Sympifyable
+        the zx element in the inertia dyadic
+
+    Examples
+    ========
+
+    >>> from sympy.physics.mechanics import ReferenceFrame, inertia
+    >>> N = ReferenceFrame('N')
+    >>> inertia(N, 1, 2, 3)
+    (N.x|N.x) + 2*(N.y|N.y) + 3*(N.z|N.z)
+
+    """
+
+    if not isinstance(frame, ReferenceFrame):
+        raise TypeError('Need to define the inertia in a frame')
+    ixx = sympify(ixx)
+    ixy = sympify(ixy)
+    iyy = sympify(iyy)
+    iyz = sympify(iyz)
+    izx = sympify(izx)
+    izz = sympify(izz)
+    ol = ixx * (frame.x | frame.x)
+    ol += ixy * (frame.x | frame.y)
+    ol += izx * (frame.x | frame.z)
+    ol += ixy * (frame.y | frame.x)
+    ol += iyy * (frame.y | frame.y)
+    ol += iyz * (frame.y | frame.z)
+    ol += izx * (frame.z | frame.x)
+    ol += iyz * (frame.z | frame.y)
+    ol += izz * (frame.z | frame.z)
+    return ol
+
+
+def inertia_of_point_mass(mass, pos_vec, frame):
+    """Inertia dyadic of a point mass relative to point O.
+
+    Parameters
+    ==========
+
+    mass : Sympifyable
+        Mass of the point mass
+    pos_vec : Vector
+        Position from point O to point mass
+    frame : ReferenceFrame
+        Reference frame to express the dyadic in
+
+    Examples
+    ========
+
+    >>> from sympy import symbols
+    >>> from sympy.physics.mechanics import ReferenceFrame, inertia_of_point_mass
+    >>> N = ReferenceFrame('N')
+    >>> r, m = symbols('r m')
+    >>> px = r * N.x
+    >>> inertia_of_point_mass(m, px, N)
+    m*r**2*(N.y|N.y) + m*r**2*(N.z|N.z)
+
+    """
+
+    return mass * (((frame.x | frame.x) + (frame.y | frame.y) +
+                   (frame.z | frame.z)) * (pos_vec & pos_vec) -
+                   (pos_vec | pos_vec))
+
+
+def linear_momentum(frame, *body):
+    """Linear momentum of the system.
+
+    Explanation
+    ===========
+
+    This function returns the linear momentum of a system of Particle's and/or
+    RigidBody's. The linear momentum of a system is equal to the vector sum of
+    the linear momentum of its constituents. Consider a system, S, comprised of
+    a rigid body, A, and a particle, P. The linear momentum of the system, L,
+    is equal to the vector sum of the linear momentum of the particle, L1, and
+    the linear momentum of the rigid body, L2, i.e.
+
+    L = L1 + L2
+
+    Parameters
+    ==========
+
+    frame : ReferenceFrame
+        The frame in which linear momentum is desired.
+    body1, body2, body3... : Particle and/or RigidBody
+        The body (or bodies) whose linear momentum is required.
+
+    Examples
+    ========
+
+    >>> from sympy.physics.mechanics import Point, Particle, ReferenceFrame
+    >>> from sympy.physics.mechanics import RigidBody, outer, linear_momentum
+    >>> N = ReferenceFrame('N')
+    >>> P = Point('P')
+    >>> P.set_vel(N, 10 * N.x)
+    >>> Pa = Particle('Pa', P, 1)
+    >>> Ac = Point('Ac')
+    >>> Ac.set_vel(N, 25 * N.y)
+    >>> I = outer(N.x, N.x)
+    >>> A = RigidBody('A', Ac, N, 20, (I, Ac))
+    >>> linear_momentum(N, A, Pa)
+    10*N.x + 500*N.y
+
+    """
+
+    if not isinstance(frame, ReferenceFrame):
+        raise TypeError('Please specify a valid ReferenceFrame')
+    else:
+        linear_momentum_sys = Vector(0)
+        for e in body:
+            if isinstance(e, (RigidBody, Particle)):
+                linear_momentum_sys += e.linear_momentum(frame)
+            else:
+                raise TypeError('*body must have only Particle or RigidBody')
+    return linear_momentum_sys
+
+
+def angular_momentum(point, frame, *body):
+    """Angular momentum of a system.
+
+    Explanation
+    ===========
+
+    This function returns the angular momentum of a system of Particle's and/or
+    RigidBody's. The angular momentum of such a system is equal to the vector
+    sum of the angular momentum of its constituents. Consider a system, S,
+    comprised of a rigid body, A, and a particle, P. The angular momentum of
+    the system, H, is equal to the vector sum of the angular momentum of the
+    particle, H1, and the angular momentum of the rigid body, H2, i.e.
+
+    H = H1 + H2
+
+    Parameters
+    ==========
+
+    point : Point
+        The point about which angular momentum of the system is desired.
+    frame : ReferenceFrame
+        The frame in which angular momentum is desired.
+    body1, body2, body3... : Particle and/or RigidBody
+        The body (or bodies) whose angular momentum is required.
+
+    Examples
+    ========
+
+    >>> from sympy.physics.mechanics import Point, Particle, ReferenceFrame
+    >>> from sympy.physics.mechanics import RigidBody, outer, angular_momentum
+    >>> N = ReferenceFrame('N')
+    >>> O = Point('O')
+    >>> O.set_vel(N, 0 * N.x)
+    >>> P = O.locatenew('P', 1 * N.x)
+    >>> P.set_vel(N, 10 * N.x)
+    >>> Pa = Particle('Pa', P, 1)
+    >>> Ac = O.locatenew('Ac', 2 * N.y)
+    >>> Ac.set_vel(N, 5 * N.y)
+    >>> a = ReferenceFrame('a')
+    >>> a.set_ang_vel(N, 10 * N.z)
+    >>> I = outer(N.z, N.z)
+    >>> A = RigidBody('A', Ac, a, 20, (I, Ac))
+    >>> angular_momentum(O, N, Pa, A)
+    10*N.z
+
+    """
+
+    if not isinstance(frame, ReferenceFrame):
+        raise TypeError('Please enter a valid ReferenceFrame')
+    if not isinstance(point, Point):
+        raise TypeError('Please specify a valid Point')
+    else:
+        angular_momentum_sys = Vector(0)
+        for e in body:
+            if isinstance(e, (RigidBody, Particle)):
+                angular_momentum_sys += e.angular_momentum(point, frame)
+            else:
+                raise TypeError('*body must have only Particle or RigidBody')
+    return angular_momentum_sys
+
+
+def kinetic_energy(frame, *body):
+    """Kinetic energy of a multibody system.
+
+    Explanation
+    ===========
+
+    This function returns the kinetic energy of a system of Particle's and/or
+    RigidBody's. The kinetic energy of such a system is equal to the sum of
+    the kinetic energies of its constituents. Consider a system, S, comprising
+    a rigid body, A, and a particle, P. The kinetic energy of the system, T,
+    is equal to the vector sum of the kinetic energy of the particle, T1, and
+    the kinetic energy of the rigid body, T2, i.e.
+
+    T = T1 + T2
+
+    Kinetic energy is a scalar.
+
+    Parameters
+    ==========
+
+    frame : ReferenceFrame
+        The frame in which the velocity or angular velocity of the body is
+        defined.
+    body1, body2, body3... : Particle and/or RigidBody
+        The body (or bodies) whose kinetic energy is required.
+
+    Examples
+    ========
+
+    >>> from sympy.physics.mechanics import Point, Particle, ReferenceFrame
+    >>> from sympy.physics.mechanics import RigidBody, outer, kinetic_energy
+    >>> N = ReferenceFrame('N')
+    >>> O = Point('O')
+    >>> O.set_vel(N, 0 * N.x)
+    >>> P = O.locatenew('P', 1 * N.x)
+    >>> P.set_vel(N, 10 * N.x)
+    >>> Pa = Particle('Pa', P, 1)
+    >>> Ac = O.locatenew('Ac', 2 * N.y)
+    >>> Ac.set_vel(N, 5 * N.y)
+    >>> a = ReferenceFrame('a')
+    >>> a.set_ang_vel(N, 10 * N.z)
+    >>> I = outer(N.z, N.z)
+    >>> A = RigidBody('A', Ac, a, 20, (I, Ac))
+    >>> kinetic_energy(N, Pa, A)
+    350
+
+    """
+
+    if not isinstance(frame, ReferenceFrame):
+        raise TypeError('Please enter a valid ReferenceFrame')
+    ke_sys = S.Zero
+    for e in body:
+        if isinstance(e, (RigidBody, Particle)):
+            ke_sys += e.kinetic_energy(frame)
+        else:
+            raise TypeError('*body must have only Particle or RigidBody')
+    return ke_sys
+
+
+def potential_energy(*body):
+    """Potential energy of a multibody system.
+
+    Explanation
+    ===========
+
+    This function returns the potential energy of a system of Particle's and/or
+    RigidBody's. The potential energy of such a system is equal to the sum of
+    the potential energy of its constituents. Consider a system, S, comprising
+    a rigid body, A, and a particle, P. The potential energy of the system, V,
+    is equal to the vector sum of the potential energy of the particle, V1, and
+    the potential energy of the rigid body, V2, i.e.
+
+    V = V1 + V2
+
+    Potential energy is a scalar.
+
+    Parameters
+    ==========
+
+    body1, body2, body3... : Particle and/or RigidBody
+        The body (or bodies) whose potential energy is required.
+
+    Examples
+    ========
+
+    >>> from sympy.physics.mechanics import Point, Particle, ReferenceFrame
+    >>> from sympy.physics.mechanics import RigidBody, outer, potential_energy
+    >>> from sympy import symbols
+    >>> M, m, g, h = symbols('M m g h')
+    >>> N = ReferenceFrame('N')
+    >>> O = Point('O')
+    >>> O.set_vel(N, 0 * N.x)
+    >>> P = O.locatenew('P', 1 * N.x)
+    >>> Pa = Particle('Pa', P, m)
+    >>> Ac = O.locatenew('Ac', 2 * N.y)
+    >>> a = ReferenceFrame('a')
+    >>> I = outer(N.z, N.z)
+    >>> A = RigidBody('A', Ac, a, M, (I, Ac))
+    >>> Pa.potential_energy = m * g * h
+    >>> A.potential_energy = M * g * h
+    >>> potential_energy(Pa, A)
+    M*g*h + g*h*m
+
+    """
+
+    pe_sys = S.Zero
+    for e in body:
+        if isinstance(e, (RigidBody, Particle)):
+            pe_sys += e.potential_energy
+        else:
+            raise TypeError('*body must have only Particle or RigidBody')
+    return pe_sys
+
+
+def gravity(acceleration, *bodies):
+    """
+    Returns a list of gravity forces given the acceleration
+    due to gravity and any number of particles or rigidbodies.
+
+    Example
+    =======
+
+    >>> from sympy.physics.mechanics import ReferenceFrame, Point, Particle, outer, RigidBody
+    >>> from sympy.physics.mechanics.functions import gravity
+    >>> from sympy import symbols
+    >>> N = ReferenceFrame('N')
+    >>> m, M, g = symbols('m M g')
+    >>> F1, F2 = symbols('F1 F2')
+    >>> po = Point('po')
+    >>> pa = Particle('pa', po, m)
+    >>> A = ReferenceFrame('A')
+    >>> P = Point('P')
+    >>> I = outer(A.x, A.x)
+    >>> B = RigidBody('B', P, A, M, (I, P))
+    >>> forceList = [(po, F1), (P, F2)]
+    >>> forceList.extend(gravity(g*N.y, pa, B))
+    >>> forceList
+    [(po, F1), (P, F2), (po, g*m*N.y), (P, M*g*N.y)]
+
+    """
+
+    gravity_force = []
+    if not bodies:
+        raise TypeError("No bodies(instances of Particle or Rigidbody) were passed.")
+
+    for e in bodies:
+        point = getattr(e, 'masscenter', None)
+        if point is None:
+            point = e.point
+
+        gravity_force.append((point, e.mass*acceleration))
+
+    return gravity_force
+
+
+def center_of_mass(point, *bodies):
+    """
+    Returns the position vector from the given point to the center of mass
+    of the given bodies(particles or rigidbodies).
+
+    Example
+    =======
+
+    >>> from sympy import symbols, S
+    >>> from sympy.physics.vector import Point
+    >>> from sympy.physics.mechanics import Particle, ReferenceFrame, RigidBody, outer
+    >>> from sympy.physics.mechanics.functions import center_of_mass
+    >>> a = ReferenceFrame('a')
+    >>> m = symbols('m', real=True)
+    >>> p1 = Particle('p1', Point('p1_pt'), S(1))
+    >>> p2 = Particle('p2', Point('p2_pt'), S(2))
+    >>> p3 = Particle('p3', Point('p3_pt'), S(3))
+    >>> p4 = Particle('p4', Point('p4_pt'), m)
+    >>> b_f = ReferenceFrame('b_f')
+    >>> b_cm = Point('b_cm')
+    >>> mb = symbols('mb')
+    >>> b = RigidBody('b', b_cm, b_f, mb, (outer(b_f.x, b_f.x), b_cm))
+    >>> p2.point.set_pos(p1.point, a.x)
+    >>> p3.point.set_pos(p1.point, a.x + a.y)
+    >>> p4.point.set_pos(p1.point, a.y)
+    >>> b.masscenter.set_pos(p1.point, a.y + a.z)
+    >>> point_o=Point('o')
+    >>> point_o.set_pos(p1.point, center_of_mass(p1.point, p1, p2, p3, p4, b))
+    >>> expr = 5/(m + mb + 6)*a.x + (m + mb + 3)/(m + mb + 6)*a.y + mb/(m + mb + 6)*a.z
+    >>> point_o.pos_from(p1.point)
+    5/(m + mb + 6)*a.x + (m + mb + 3)/(m + mb + 6)*a.y + mb/(m + mb + 6)*a.z
+
+    """
+    if not bodies:
+        raise TypeError("No bodies(instances of Particle or Rigidbody) were passed.")
+
+    total_mass = 0
+    vec = Vector(0)
+    for i in bodies:
+        total_mass += i.mass
+
+        masscenter = getattr(i, 'masscenter', None)
+        if masscenter is None:
+            masscenter = i.point
+        vec += i.mass*masscenter.pos_from(point)
+
+    return vec/total_mass
+
+
+def Lagrangian(frame, *body):
+    """Lagrangian of a multibody system.
+
+    Explanation
+    ===========
+
+    This function returns the Lagrangian of a system of Particle's and/or
+    RigidBody's. The Lagrangian of such a system is equal to the difference
+    between the kinetic energies and potential energies of its constituents. If
+    T and V are the kinetic and potential energies of a system then it's
+    Lagrangian, L, is defined as
+
+    L = T - V
+
+    The Lagrangian is a scalar.
+
+    Parameters
+    ==========
+
+    frame : ReferenceFrame
+        The frame in which the velocity or angular velocity of the body is
+        defined to determine the kinetic energy.
+
+    body1, body2, body3... : Particle and/or RigidBody
+        The body (or bodies) whose Lagrangian is required.
+
+    Examples
+    ========
+
+    >>> from sympy.physics.mechanics import Point, Particle, ReferenceFrame
+    >>> from sympy.physics.mechanics import RigidBody, outer, Lagrangian
+    >>> from sympy import symbols
+    >>> M, m, g, h = symbols('M m g h')
+    >>> N = ReferenceFrame('N')
+    >>> O = Point('O')
+    >>> O.set_vel(N, 0 * N.x)
+    >>> P = O.locatenew('P', 1 * N.x)
+    >>> P.set_vel(N, 10 * N.x)
+    >>> Pa = Particle('Pa', P, 1)
+    >>> Ac = O.locatenew('Ac', 2 * N.y)
+    >>> Ac.set_vel(N, 5 * N.y)
+    >>> a = ReferenceFrame('a')
+    >>> a.set_ang_vel(N, 10 * N.z)
+    >>> I = outer(N.z, N.z)
+    >>> A = RigidBody('A', Ac, a, 20, (I, Ac))
+    >>> Pa.potential_energy = m * g * h
+    >>> A.potential_energy = M * g * h
+    >>> Lagrangian(N, Pa, A)
+    -M*g*h - g*h*m + 350
+
+    """
+
+    if not isinstance(frame, ReferenceFrame):
+        raise TypeError('Please supply a valid ReferenceFrame')
+    for e in body:
+        if not isinstance(e, (RigidBody, Particle)):
+            raise TypeError('*body must have only Particle or RigidBody')
+    return kinetic_energy(frame, *body) - potential_energy(*body)
+
+
+def find_dynamicsymbols(expression, exclude=None, reference_frame=None):
+    """Find all dynamicsymbols in expression.
+
+    Explanation
+    ===========
+
+    If the optional ``exclude`` kwarg is used, only dynamicsymbols
+    not in the iterable ``exclude`` are returned.
+    If we intend to apply this function on a vector, the optional
+    ``reference_frame`` is also used to inform about the corresponding frame
+    with respect to which the dynamic symbols of the given vector is to be
+    determined.
+
+    Parameters
+    ==========
+
+    expression : SymPy expression
+
+    exclude : iterable of dynamicsymbols, optional
+
+    reference_frame : ReferenceFrame, optional
+        The frame with respect to which the dynamic symbols of the
+        given vector is to be determined.
+
+    Examples
+    ========
+
+    >>> from sympy.physics.mechanics import dynamicsymbols, find_dynamicsymbols
+    >>> from sympy.physics.mechanics import ReferenceFrame
+    >>> x, y = dynamicsymbols('x, y')
+    >>> expr = x + x.diff()*y
+    >>> find_dynamicsymbols(expr)
+    {x(t), y(t), Derivative(x(t), t)}
+    >>> find_dynamicsymbols(expr, exclude=[x, y])
+    {Derivative(x(t), t)}
+    >>> a, b, c = dynamicsymbols('a, b, c')
+    >>> A = ReferenceFrame('A')
+    >>> v = a * A.x + b * A.y + c * A.z
+    >>> find_dynamicsymbols(v, reference_frame=A)
+    {a(t), b(t), c(t)}
+
+    """
+    t_set = {dynamicsymbols._t}
+    if exclude:
+        if iterable(exclude):
+            exclude_set = set(exclude)
+        else:
+            raise TypeError("exclude kwarg must be iterable")
+    else:
+        exclude_set = set()
+    if isinstance(expression, Vector):
+        if reference_frame is None:
+            raise ValueError("You must provide reference_frame when passing a "
+                             "vector expression, got %s." % reference_frame)
+        else:
+            expression = expression.to_matrix(reference_frame)
+    return {i for i in expression.atoms(AppliedUndef, Derivative) if
+            i.free_symbols == t_set} - exclude_set
+
+
+def msubs(expr, *sub_dicts, smart=False, **kwargs):
+    """A custom subs for use on expressions derived in physics.mechanics.
+
+    Traverses the expression tree once, performing the subs found in sub_dicts.
+    Terms inside ``Derivative`` expressions are ignored:
+
+    Examples
+    ========
+
+    >>> from sympy.physics.mechanics import dynamicsymbols, msubs
+    >>> x = dynamicsymbols('x')
+    >>> msubs(x.diff() + x, {x: 1})
+    Derivative(x(t), t) + 1
+
+    Note that sub_dicts can be a single dictionary, or several dictionaries:
+
+    >>> x, y, z = dynamicsymbols('x, y, z')
+    >>> sub1 = {x: 1, y: 2}
+    >>> sub2 = {z: 3, x.diff(): 4}
+    >>> msubs(x.diff() + x + y + z, sub1, sub2)
+    10
+
+    If smart=True (default False), also checks for conditions that may result
+    in ``nan``, but if simplified would yield a valid expression. For example:
+
+    >>> from sympy import sin, tan
+    >>> (sin(x)/tan(x)).subs(x, 0)
+    nan
+    >>> msubs(sin(x)/tan(x), {x: 0}, smart=True)
+    1
+
+    It does this by first replacing all ``tan`` with ``sin/cos``. Then each
+    node is traversed. If the node is a fraction, subs is first evaluated on
+    the denominator. If this results in 0, simplification of the entire
+    fraction is attempted. Using this selective simplification, only
+    subexpressions that result in 1/0 are targeted, resulting in faster
+    performance.
+
+    """
+
+    sub_dict = dict_merge(*sub_dicts)
+    if smart:
+        func = _smart_subs
+    elif hasattr(expr, 'msubs'):
+        return expr.msubs(sub_dict)
+    else:
+        func = lambda expr, sub_dict: _crawl(expr, _sub_func, sub_dict)
+    if isinstance(expr, (Matrix, Vector, Dyadic)):
+        return expr.applyfunc(lambda x: func(x, sub_dict))
+    else:
+        return func(expr, sub_dict)
+
+
+def _crawl(expr, func, *args, **kwargs):
+    """Crawl the expression tree, and apply func to every node."""
+    val = func(expr, *args, **kwargs)
+    if val is not None:
+        return val
+    new_args = (_crawl(arg, func, *args, **kwargs) for arg in expr.args)
+    return expr.func(*new_args)
+
+
+def _sub_func(expr, sub_dict):
+    """Perform direct matching substitution, ignoring derivatives."""
+    if expr in sub_dict:
+        return sub_dict[expr]
+    elif not expr.args or expr.is_Derivative:
+        return expr
+
+
+def _tan_repl_func(expr):
+    """Replace tan with sin/cos."""
+    if isinstance(expr, tan):
+        return sin(*expr.args) / cos(*expr.args)
+    elif not expr.args or expr.is_Derivative:
+        return expr
+
+
+def _smart_subs(expr, sub_dict):
+    """Performs subs, checking for conditions that may result in `nan` or
+    `oo`, and attempts to simplify them out.
+
+    The expression tree is traversed twice, and the following steps are
+    performed on each expression node:
+    - First traverse:
+        Replace all `tan` with `sin/cos`.
+    - Second traverse:
+        If node is a fraction, check if the denominator evaluates to 0.
+        If so, attempt to simplify it out. Then if node is in sub_dict,
+        sub in the corresponding value.
+
+    """
+    expr = _crawl(expr, _tan_repl_func)
+
+    def _recurser(expr, sub_dict):
+        # Decompose the expression into num, den
+        num, den = _fraction_decomp(expr)
+        if den != 1:
+            # If there is a non trivial denominator, we need to handle it
+            denom_subbed = _recurser(den, sub_dict)
+            if denom_subbed.evalf() == 0:
+                # If denom is 0 after this, attempt to simplify the bad expr
+                expr = simplify(expr)
+            else:
+                # Expression won't result in nan, find numerator
+                num_subbed = _recurser(num, sub_dict)
+                return num_subbed / denom_subbed
+        # We have to crawl the tree manually, because `expr` may have been
+        # modified in the simplify step. First, perform subs as normal:
+        val = _sub_func(expr, sub_dict)
+        if val is not None:
+            return val
+        new_args = (_recurser(arg, sub_dict) for arg in expr.args)
+        return expr.func(*new_args)
+    return _recurser(expr, sub_dict)
+
+
+def _fraction_decomp(expr):
+    """Return num, den such that expr = num/den."""
+    if not isinstance(expr, Mul):
+        return expr, 1
+    num = []
+    den = []
+    for a in expr.args:
+        if a.is_Pow and a.args[1] < 0:
+            den.append(1 / a)
+        else:
+            num.append(a)
+    if not den:
+        return expr, 1
+    num = Mul(*num)
+    den = Mul(*den)
+    return num, den
+
+
+def _f_list_parser(fl, ref_frame):
+    """Parses the provided forcelist composed of items
+    of the form (obj, force).
+    Returns a tuple containing:
+        vel_list: The velocity (ang_vel for Frames, vel for Points) in
+                the provided reference frame.
+        f_list: The forces.
+
+    Used internally in the KanesMethod and LagrangesMethod classes.
+
+    """
+    def flist_iter():
+        for pair in fl:
+            obj, force = pair
+            if isinstance(obj, ReferenceFrame):
+                yield obj.ang_vel_in(ref_frame), force
+            elif isinstance(obj, Point):
+                yield obj.vel(ref_frame), force
+            else:
+                raise TypeError('First entry in each forcelist pair must '
+                                'be a point or frame.')
+
+    if not fl:
+        vel_list, f_list = (), ()
+    else:
+        unzip = lambda l: list(zip(*l)) if l[0] else [(), ()]
+        vel_list, f_list = unzip(list(flist_iter()))
+    return vel_list, f_list
+
+
+def _validate_coordinates(coordinates=None, speeds=None, check_duplicates=True,
+                          is_dynamicsymbols=True):
+    t_set = {dynamicsymbols._t}
+    # Convert input to iterables
+    if coordinates is None:
+        coordinates = []
+    elif not iterable(coordinates):
+        coordinates = [coordinates]
+    if speeds is None:
+        speeds = []
+    elif not iterable(speeds):
+        speeds = [speeds]
+
+    if check_duplicates:  # Check for duplicates
+        seen = set()
+        coord_duplicates = {x for x in coordinates if x in seen or seen.add(x)}
+        seen = set()
+        speed_duplicates = {x for x in speeds if x in seen or seen.add(x)}
+        overlap = set(coordinates).intersection(speeds)
+        if coord_duplicates:
+            raise ValueError(f'The generalized coordinates {coord_duplicates} '
+                             f'are duplicated, all generalized coordinates '
+                             f'should be unique.')
+        if speed_duplicates:
+            raise ValueError(f'The generalized speeds {speed_duplicates} are '
+                             f'duplicated, all generalized speeds should be '
+                             f'unique.')
+        if overlap:
+            raise ValueError(f'{overlap} are defined as both generalized '
+                             f'coordinates and generalized speeds.')
+    if is_dynamicsymbols:  # Check whether all coordinates are dynamicsymbols
+        for coordinate in coordinates:
+            if not (isinstance(coordinate, (AppliedUndef, Derivative)) and
+                    coordinate.free_symbols == t_set):
+                raise ValueError(f'Generalized coordinate "{coordinate}" is not'
+                                 f' a dynamicsymbol.')
+        for speed in speeds:
+            if not (isinstance(speed, (AppliedUndef, Derivative)) and
+                    speed.free_symbols == t_set):
+                raise ValueError(f'Generalized speed "{speed}" is not a '
+                                 f'dynamicsymbol.')

venv/lib/python3.10/site-packages/sympy/physics/mechanics/joint.py

@@ -0,0 +1,2163 @@
+# coding=utf-8
+
+from abc import ABC, abstractmethod
+
+from sympy.core.backend import pi, AppliedUndef, Derivative, Matrix
+from sympy.physics.mechanics.body import Body
+from sympy.physics.mechanics.functions import _validate_coordinates
+from sympy.physics.vector import (Vector, dynamicsymbols, cross, Point,
+                                  ReferenceFrame)
+from sympy.utilities.iterables import iterable
+from sympy.utilities.exceptions import sympy_deprecation_warning
+
+__all__ = ['Joint', 'PinJoint', 'PrismaticJoint', 'CylindricalJoint',
+           'PlanarJoint', 'SphericalJoint', 'WeldJoint']
+
+
+class Joint(ABC):
+    """Abstract base class for all specific joints.
+
+    Explanation
+    ===========
+
+    A joint subtracts degrees of freedom from a body. This is the base class
+    for all specific joints and holds all common methods acting as an interface
+    for all joints. Custom joint can be created by inheriting Joint class and
+    defining all abstract functions.
+
+    The abstract methods are:
+
+    - ``_generate_coordinates``
+    - ``_generate_speeds``
+    - ``_orient_frames``
+    - ``_set_angular_velocity``
+    - ``_set_linear_velocity``
+
+    Parameters
+    ==========
+
+    name : string
+        A unique name for the joint.
+    parent : Body
+        The parent body of joint.
+    child : Body
+        The child body of joint.
+    coordinates : iterable of dynamicsymbols, optional
+        Generalized coordinates of the joint.
+    speeds : iterable of dynamicsymbols, optional
+        Generalized speeds of joint.
+    parent_point : Point or Vector, optional
+        Attachment point where the joint is fixed to the parent body. If a
+        vector is provided, then the attachment point is computed by adding the
+        vector to the body's mass center. The default value is the parent's mass
+        center.
+    child_point : Point or Vector, optional
+        Attachment point where the joint is fixed to the child body. If a
+        vector is provided, then the attachment point is computed by adding the
+        vector to the body's mass center. The default value is the child's mass
+        center.
+    parent_axis : Vector, optional
+        .. deprecated:: 1.12
+            Axis fixed in the parent body which aligns with an axis fixed in the
+            child body. The default is the x axis of parent's reference frame.
+            For more information on this deprecation, see
+            :ref:`deprecated-mechanics-joint-axis`.
+    child_axis : Vector, optional
+        .. deprecated:: 1.12
+            Axis fixed in the child body which aligns with an axis fixed in the
+            parent body. The default is the x axis of child's reference frame.
+            For more information on this deprecation, see
+            :ref:`deprecated-mechanics-joint-axis`.
+    parent_interframe : ReferenceFrame, optional
+        Intermediate frame of the parent body with respect to which the joint
+        transformation is formulated. If a Vector is provided then an interframe
+        is created which aligns its X axis with the given vector. The default
+        value is the parent's own frame.
+    child_interframe : ReferenceFrame, optional
+        Intermediate frame of the child body with respect to which the joint
+        transformation is formulated. If a Vector is provided then an interframe
+        is created which aligns its X axis with the given vector. The default
+        value is the child's own frame.
+    parent_joint_pos : Point or Vector, optional
+        .. deprecated:: 1.12
+            This argument is replaced by parent_point and will be removed in a
+            future version.
+            See :ref:`deprecated-mechanics-joint-pos` for more information.
+    child_joint_pos : Point or Vector, optional
+        .. deprecated:: 1.12
+            This argument is replaced by child_point and will be removed in a
+            future version.
+            See :ref:`deprecated-mechanics-joint-pos` for more information.
+
+    Attributes
+    ==========
+
+    name : string
+        The joint's name.
+    parent : Body
+        The joint's parent body.
+    child : Body
+        The joint's child body.
+    coordinates : Matrix
+        Matrix of the joint's generalized coordinates.
+    speeds : Matrix
+        Matrix of the joint's generalized speeds.
+    parent_point : Point
+        Attachment point where the joint is fixed to the parent body.
+    child_point : Point
+        Attachment point where the joint is fixed to the child body.
+    parent_axis : Vector
+        The axis fixed in the parent frame that represents the joint.
+    child_axis : Vector
+        The axis fixed in the child frame that represents the joint.
+    parent_interframe : ReferenceFrame
+        Intermediate frame of the parent body with respect to which the joint
+        transformation is formulated.
+    child_interframe : ReferenceFrame
+        Intermediate frame of the child body with respect to which the joint
+        transformation is formulated.
+    kdes : Matrix
+        Kinematical differential equations of the joint.
+
+    Notes
+    =====
+
+    When providing a vector as the intermediate frame, a new intermediate frame
+    is created which aligns its X axis with the provided vector. This is done
+    with a single fixed rotation about a rotation axis. This rotation axis is
+    determined by taking the cross product of the ``body.x`` axis with the
+    provided vector. In the case where the provided vector is in the ``-body.x``
+    direction, the rotation is done about the ``body.y`` axis.
+
+    """
+
+    def __init__(self, name, parent, child, coordinates=None, speeds=None,
+                 parent_point=None, child_point=None, parent_axis=None,
+                 child_axis=None, parent_interframe=None, child_interframe=None,
+                 parent_joint_pos=None, child_joint_pos=None):
+
+        if not isinstance(name, str):
+            raise TypeError('Supply a valid name.')
+        self._name = name
+
+        if not isinstance(parent, Body):
+            raise TypeError('Parent must be an instance of Body.')
+        self._parent = parent
+
+        if not isinstance(child, Body):
+            raise TypeError('Parent must be an instance of Body.')
+        self._child = child
+
+        self._coordinates = self._generate_coordinates(coordinates)
+        self._speeds = self._generate_speeds(speeds)
+        _validate_coordinates(self.coordinates, self.speeds)
+        self._kdes = self._generate_kdes()
+
+        self._parent_axis = self._axis(parent_axis, parent.frame)
+        self._child_axis = self._axis(child_axis, child.frame)
+
+        if parent_joint_pos is not None or child_joint_pos is not None:
+            sympy_deprecation_warning(
+                """
+                The parent_joint_pos and child_joint_pos arguments for the Joint
+                classes are deprecated. Instead use parent_point and child_point.
+                """,
+                deprecated_since_version="1.12",
+                active_deprecations_target="deprecated-mechanics-joint-pos",
+                stacklevel=4
+            )
+            if parent_point is None:
+                parent_point = parent_joint_pos
+            if child_point is None:
+                child_point = child_joint_pos
+        self._parent_point = self._locate_joint_pos(parent, parent_point)
+        self._child_point = self._locate_joint_pos(child, child_point)
+        if parent_axis is not None or child_axis is not None:
+            sympy_deprecation_warning(
+                """
+                The parent_axis and child_axis arguments for the Joint classes
+                are deprecated. Instead use parent_interframe, child_interframe.
+                """,
+                deprecated_since_version="1.12",
+                active_deprecations_target="deprecated-mechanics-joint-axis",
+                stacklevel=4
+            )
+            if parent_interframe is None:
+                parent_interframe = parent_axis
+            if child_interframe is None:
+                child_interframe = child_axis
+        self._parent_interframe = self._locate_joint_frame(parent,
+                                                           parent_interframe)
+        self._child_interframe = self._locate_joint_frame(child,
+                                                          child_interframe)
+
+        self._orient_frames()
+        self._set_angular_velocity()
+        self._set_linear_velocity()
+
+    def __str__(self):
+        return self.name
+
+    def __repr__(self):
+        return self.__str__()
+
+    @property
+    def name(self):
+        """Name of the joint."""
+        return self._name
+
+    @property
+    def parent(self):
+        """Parent body of Joint."""
+        return self._parent
+
+    @property
+    def child(self):
+        """Child body of Joint."""
+        return self._child
+
+    @property
+    def coordinates(self):
+        """Matrix of the joint's generalized coordinates."""
+        return self._coordinates
+
+    @property
+    def speeds(self):
+        """Matrix of the joint's generalized speeds."""
+        return self._speeds
+
+    @property
+    def kdes(self):
+        """Kinematical differential equations of the joint."""
+        return self._kdes
+
+    @property
+    def parent_axis(self):
+        """The axis of parent frame."""
+        # Will be removed with `deprecated-mechanics-joint-axis`
+        return self._parent_axis
+
+    @property
+    def child_axis(self):
+        """The axis of child frame."""
+        # Will be removed with `deprecated-mechanics-joint-axis`
+        return self._child_axis
+
+    @property
+    def parent_point(self):
+        """Attachment point where the joint is fixed to the parent body."""
+        return self._parent_point
+
+    @property
+    def child_point(self):
+        """Attachment point where the joint is fixed to the child body."""
+        return self._child_point
+
+    @property
+    def parent_interframe(self):
+        return self._parent_interframe
+
+    @property
+    def child_interframe(self):
+        return self._child_interframe
+
+    @abstractmethod
+    def _generate_coordinates(self, coordinates):
+        """Generate Matrix of the joint's generalized coordinates."""
+        pass
+
+    @abstractmethod
+    def _generate_speeds(self, speeds):
+        """Generate Matrix of the joint's generalized speeds."""
+        pass
+
+    @abstractmethod
+    def _orient_frames(self):
+        """Orient frames as per the joint."""
+        pass
+
+    @abstractmethod
+    def _set_angular_velocity(self):
+        """Set angular velocity of the joint related frames."""
+        pass
+
+    @abstractmethod
+    def _set_linear_velocity(self):
+        """Set velocity of related points to the joint."""
+        pass
+
+    @staticmethod
+    def _to_vector(matrix, frame):
+        """Converts a matrix to a vector in the given frame."""
+        return Vector([(matrix, frame)])
+
+    @staticmethod
+    def _axis(ax, *frames):
+        """Check whether an axis is fixed in one of the frames."""
+        if ax is None:
+            ax = frames[0].x
+            return ax
+        if not isinstance(ax, Vector):
+            raise TypeError("Axis must be a Vector.")
+        ref_frame = None  # Find a body in which the axis can be expressed
+        for frame in frames:
+            try:
+                ax.to_matrix(frame)
+            except ValueError:
+                pass
+            else:
+                ref_frame = frame
+                break
+        if ref_frame is None:
+            raise ValueError("Axis cannot be expressed in one of the body's "
+                             "frames.")
+        if not ax.dt(ref_frame) == 0:
+            raise ValueError('Axis cannot be time-varying when viewed from the '
+                             'associated body.')
+        return ax
+
+    @staticmethod
+    def _choose_rotation_axis(frame, axis):
+        components = axis.to_matrix(frame)
+        x, y, z = components[0], components[1], components[2]
+
+        if x != 0:
+            if y != 0:
+                if z != 0:
+                    return cross(axis, frame.x)
+            if z != 0:
+                return frame.y
+            return frame.z
+        else:
+            if y != 0:
+                return frame.x
+            return frame.y
+
+    @staticmethod
+    def _create_aligned_interframe(frame, align_axis, frame_axis=None,
+                                   frame_name=None):
+        """
+        Returns an intermediate frame, where the ``frame_axis`` defined in
+        ``frame`` is aligned with ``axis``. By default this means that the X
+        axis will be aligned with ``axis``.
+
+        Parameters
+        ==========
+
+        frame : Body or ReferenceFrame
+            The body or reference frame with respect to which the intermediate
+            frame is oriented.
+        align_axis : Vector
+            The vector with respect to which the intermediate frame will be
+            aligned.
+        frame_axis : Vector
+            The vector of the frame which should get aligned with ``axis``. The
+            default is the X axis of the frame.
+        frame_name : string
+            Name of the to be created intermediate frame. The default adds
+            "_int_frame" to the name of ``frame``.
+
+        Example
+        =======
+
+        An intermediate frame, where the X axis of the parent becomes aligned
+        with ``parent.y + parent.z`` can be created as follows:
+
+        >>> from sympy.physics.mechanics.joint import Joint
+        >>> from sympy.physics.mechanics import Body
+        >>> parent = Body('parent')
+        >>> parent_interframe = Joint._create_aligned_interframe(
+        ...     parent, parent.y + parent.z)
+        >>> parent_interframe
+        parent_int_frame
+        >>> parent.dcm(parent_interframe)
+        Matrix([
+        [        0, -sqrt(2)/2, -sqrt(2)/2],
+        [sqrt(2)/2,        1/2,       -1/2],
+        [sqrt(2)/2,       -1/2,        1/2]])
+        >>> (parent.y + parent.z).express(parent_interframe)
+        sqrt(2)*parent_int_frame.x
+
+        Notes
+        =====
+
+        The direction cosine matrix between the given frame and intermediate
+        frame is formed using a simple rotation about an axis that is normal to
+        both ``align_axis`` and ``frame_axis``. In general, the normal axis is
+        formed by crossing the ``frame_axis`` with the ``align_axis``. The
+        exception is if the axes are parallel with opposite directions, in which
+        case the rotation vector is chosen using the rules in the following
+        table with the vectors expressed in the given frame:
+
+        .. list-table::
+           :header-rows: 1
+
+           * - ``align_axis``
+             - ``frame_axis``
+             - ``rotation_axis``
+           * - ``-x``
+             - ``x``
+             - ``z``
+           * - ``-y``
+             - ``y``
+             - ``x``
+           * - ``-z``
+             - ``z``
+             - ``y``
+           * - ``-x-y``
+             - ``x+y``
+             - ``z``
+           * - ``-y-z``
+             - ``y+z``
+             - ``x``
+           * - ``-x-z``
+             - ``x+z``
+             - ``y``
+           * - ``-x-y-z``
+             - ``x+y+z``
+             - ``(x+y+z) × x``
+
+        """
+        if isinstance(frame, Body):
+            frame = frame.frame
+        if frame_axis is None:
+            frame_axis = frame.x
+        if frame_name is None:
+            if frame.name[-6:] == '_frame':
+                frame_name = f'{frame.name[:-6]}_int_frame'
+            else:
+                frame_name = f'{frame.name}_int_frame'
+        angle = frame_axis.angle_between(align_axis)
+        rotation_axis = cross(frame_axis, align_axis)
+        if rotation_axis == Vector(0) and angle == 0:
+            return frame
+        if angle == pi:
+            rotation_axis = Joint._choose_rotation_axis(frame, align_axis)
+
+        int_frame = ReferenceFrame(frame_name)
+        int_frame.orient_axis(frame, rotation_axis, angle)
+        int_frame.set_ang_vel(frame, 0 * rotation_axis)
+        return int_frame
+
+    def _generate_kdes(self):
+        """Generate kinematical differential equations."""
+        kdes = []
+        t = dynamicsymbols._t
+        for i in range(len(self.coordinates)):
+            kdes.append(-self.coordinates[i].diff(t) + self.speeds[i])
+        return Matrix(kdes)
+
+    def _locate_joint_pos(self, body, joint_pos):
+        """Returns the attachment point of a body."""
+        if joint_pos is None:
+            return body.masscenter
+        if not isinstance(joint_pos, (Point, Vector)):
+            raise TypeError('Attachment point must be a Point or Vector.')
+        if isinstance(joint_pos, Vector):
+            point_name = f'{self.name}_{body.name}_joint'
+            joint_pos = body.masscenter.locatenew(point_name, joint_pos)
+        if not joint_pos.pos_from(body.masscenter).dt(body.frame) == 0:
+            raise ValueError('Attachment point must be fixed to the associated '
+                             'body.')
+        return joint_pos
+
+    def _locate_joint_frame(self, body, interframe):
+        """Returns the attachment frame of a body."""
+        if interframe is None:
+            return body.frame
+        if isinstance(interframe, Vector):
+            interframe = Joint._create_aligned_interframe(
+                body, interframe,
+                frame_name=f'{self.name}_{body.name}_int_frame')
+        elif not isinstance(interframe, ReferenceFrame):
+            raise TypeError('Interframe must be a ReferenceFrame.')
+        if not interframe.ang_vel_in(body.frame) == 0:
+            raise ValueError(f'Interframe {interframe} is not fixed to body '
+                             f'{body}.')
+        body.masscenter.set_vel(interframe, 0)  # Fixate interframe to body
+        return interframe
+
+    def _fill_coordinate_list(self, coordinates, n_coords, label='q', offset=0,
+                              number_single=False):
+        """Helper method for _generate_coordinates and _generate_speeds.
+
+        Parameters
+        ==========
+
+        coordinates : iterable
+            Iterable of coordinates or speeds that have been provided.
+        n_coords : Integer
+            Number of coordinates that should be returned.
+        label : String, optional
+            Coordinate type either 'q' (coordinates) or 'u' (speeds). The
+            Default is 'q'.
+        offset : Integer
+            Count offset when creating new dynamicsymbols. The default is 0.
+        number_single : Boolean
+            Boolean whether if n_coords == 1, number should still be used. The
+            default is False.
+
+        """
+
+        def create_symbol(number):
+            if n_coords == 1 and not number_single:
+                return dynamicsymbols(f'{label}_{self.name}')
+            return dynamicsymbols(f'{label}{number}_{self.name}')
+
+        name = 'generalized coordinate' if label == 'q' else 'generalized speed'
+        generated_coordinates = []
+        if coordinates is None:
+            coordinates = []
+        elif not iterable(coordinates):
+            coordinates = [coordinates]
+        if not (len(coordinates) == 0 or len(coordinates) == n_coords):
+            raise ValueError(f'Expected {n_coords} {name}s, instead got '
+                             f'{len(coordinates)} {name}s.')
+        # Supports more iterables, also Matrix
+        for i, coord in enumerate(coordinates):
+            if coord is None:
+                generated_coordinates.append(create_symbol(i + offset))
+            elif isinstance(coord, (AppliedUndef, Derivative)):
+                generated_coordinates.append(coord)
+            else:
+                raise TypeError(f'The {name} {coord} should have been a '
+                                f'dynamicsymbol.')
+        for i in range(len(coordinates) + offset, n_coords + offset):
+            generated_coordinates.append(create_symbol(i))
+        return Matrix(generated_coordinates)
+
+
+class PinJoint(Joint):
+    """Pin (Revolute) Joint.
+
+    .. image:: PinJoint.svg
+
+    Explanation
+    ===========
+
+    A pin joint is defined such that the joint rotation axis is fixed in both
+    the child and parent and the location of the joint is relative to the mass
+    center of each body. The child rotates an angle, θ, from the parent about
+    the rotation axis and has a simple angular speed, ω, relative to the
+    parent. The direction cosine matrix between the child interframe and
+    parent interframe is formed using a simple rotation about the joint axis.
+    The page on the joints framework gives a more detailed explanation of the
+    intermediate frames.
+
+    Parameters
+    ==========
+
+    name : string
+        A unique name for the joint.
+    parent : Body
+        The parent body of joint.
+    child : Body
+        The child body of joint.
+    coordinates : dynamicsymbol, optional
+        Generalized coordinates of the joint.
+    speeds : dynamicsymbol, optional
+        Generalized speeds of joint.
+    parent_point : Point or Vector, optional
+        Attachment point where the joint is fixed to the parent body. If a
+        vector is provided, then the attachment point is computed by adding the
+        vector to the body's mass center. The default value is the parent's mass
+        center.
+    child_point : Point or Vector, optional
+        Attachment point where the joint is fixed to the child body. If a
+        vector is provided, then the attachment point is computed by adding the
+        vector to the body's mass center. The default value is the child's mass
+        center.
+    parent_axis : Vector, optional
+        .. deprecated:: 1.12
+            Axis fixed in the parent body which aligns with an axis fixed in the
+            child body. The default is the x axis of parent's reference frame.
+            For more information on this deprecation, see
+            :ref:`deprecated-mechanics-joint-axis`.
+    child_axis : Vector, optional
+        .. deprecated:: 1.12
+            Axis fixed in the child body which aligns with an axis fixed in the
+            parent body. The default is the x axis of child's reference frame.
+            For more information on this deprecation, see
+            :ref:`deprecated-mechanics-joint-axis`.
+    parent_interframe : ReferenceFrame, optional
+        Intermediate frame of the parent body with respect to which the joint
+        transformation is formulated. If a Vector is provided then an interframe
+        is created which aligns its X axis with the given vector. The default
+        value is the parent's own frame.
+    child_interframe : ReferenceFrame, optional
+        Intermediate frame of the child body with respect to which the joint
+        transformation is formulated. If a Vector is provided then an interframe
+        is created which aligns its X axis with the given vector. The default
+        value is the child's own frame.
+    joint_axis : Vector
+        The axis about which the rotation occurs. Note that the components
+        of this axis are the same in the parent_interframe and child_interframe.
+    parent_joint_pos : Point or Vector, optional
+        .. deprecated:: 1.12
+            This argument is replaced by parent_point and will be removed in a
+            future version.
+            See :ref:`deprecated-mechanics-joint-pos` for more information.
+    child_joint_pos : Point or Vector, optional
+        .. deprecated:: 1.12
+            This argument is replaced by child_point and will be removed in a
+            future version.
+            See :ref:`deprecated-mechanics-joint-pos` for more information.
+
+    Attributes
+    ==========
+
+    name : string
+        The joint's name.
+    parent : Body
+        The joint's parent body.
+    child : Body
+        The joint's child body.
+    coordinates : Matrix
+        Matrix of the joint's generalized coordinates. The default value is
+        ``dynamicsymbols(f'q_{joint.name}')``.
+    speeds : Matrix
+        Matrix of the joint's generalized speeds. The default value is
+        ``dynamicsymbols(f'u_{joint.name}')``.
+    parent_point : Point
+        Attachment point where the joint is fixed to the parent body.
+    child_point : Point
+        Attachment point where the joint is fixed to the child body.
+    parent_axis : Vector
+        The axis fixed in the parent frame that represents the joint.
+    child_axis : Vector
+        The axis fixed in the child frame that represents the joint.
+    parent_interframe : ReferenceFrame
+        Intermediate frame of the parent body with respect to which the joint
+        transformation is formulated.
+    child_interframe : ReferenceFrame
+        Intermediate frame of the child body with respect to which the joint
+        transformation is formulated.
+    joint_axis : Vector
+        The axis about which the rotation occurs. Note that the components of
+        this axis are the same in the parent_interframe and child_interframe.
+    kdes : Matrix
+        Kinematical differential equations of the joint.
+
+    Examples
+    =========
+
+    A single pin joint is created from two bodies and has the following basic
+    attributes:
+
+    >>> from sympy.physics.mechanics import Body, PinJoint
+    >>> parent = Body('P')
+    >>> parent
+    P
+    >>> child = Body('C')
+    >>> child
+    C
+    >>> joint = PinJoint('PC', parent, child)
+    >>> joint
+    PinJoint: PC  parent: P  child: C
+    >>> joint.name
+    'PC'
+    >>> joint.parent
+    P
+    >>> joint.child
+    C
+    >>> joint.parent_point
+    P_masscenter
+    >>> joint.child_point
+    C_masscenter
+    >>> joint.parent_axis
+    P_frame.x
+    >>> joint.child_axis
+    C_frame.x
+    >>> joint.coordinates
+    Matrix([[q_PC(t)]])
+    >>> joint.speeds
+    Matrix([[u_PC(t)]])
+    >>> joint.child.frame.ang_vel_in(joint.parent.frame)
+    u_PC(t)*P_frame.x
+    >>> joint.child.frame.dcm(joint.parent.frame)
+    Matrix([
+    [1,             0,            0],
+    [0,  cos(q_PC(t)), sin(q_PC(t))],
+    [0, -sin(q_PC(t)), cos(q_PC(t))]])
+    >>> joint.child_point.pos_from(joint.parent_point)
+    0
+
+    To further demonstrate the use of the pin joint, the kinematics of simple
+    double pendulum that rotates about the Z axis of each connected body can be
+    created as follows.
+
+    >>> from sympy import symbols, trigsimp
+    >>> from sympy.physics.mechanics import Body, PinJoint
+    >>> l1, l2 = symbols('l1 l2')
+
+    First create bodies to represent the fixed ceiling and one to represent
+    each pendulum bob.
+
+    >>> ceiling = Body('C')
+    >>> upper_bob = Body('U')
+    >>> lower_bob = Body('L')
+
+    The first joint will connect the upper bob to the ceiling by a distance of
+    ``l1`` and the joint axis will be about the Z axis for each body.
+
+    >>> ceiling_joint = PinJoint('P1', ceiling, upper_bob,
+    ... child_point=-l1*upper_bob.frame.x,
+    ... joint_axis=ceiling.frame.z)
+
+    The second joint will connect the lower bob to the upper bob by a distance
+    of ``l2`` and the joint axis will also be about the Z axis for each body.
+
+    >>> pendulum_joint = PinJoint('P2', upper_bob, lower_bob,
+    ... child_point=-l2*lower_bob.frame.x,
+    ... joint_axis=upper_bob.frame.z)
+
+    Once the joints are established the kinematics of the connected bodies can
+    be accessed. First the direction cosine matrices of pendulum link relative
+    to the ceiling are found:
+
+    >>> upper_bob.frame.dcm(ceiling.frame)
+    Matrix([
+    [ cos(q_P1(t)), sin(q_P1(t)), 0],
+    [-sin(q_P1(t)), cos(q_P1(t)), 0],
+    [            0,            0, 1]])
+    >>> trigsimp(lower_bob.frame.dcm(ceiling.frame))
+    Matrix([
+    [ cos(q_P1(t) + q_P2(t)), sin(q_P1(t) + q_P2(t)), 0],
+    [-sin(q_P1(t) + q_P2(t)), cos(q_P1(t) + q_P2(t)), 0],
+    [                      0,                      0, 1]])
+
+    The position of the lower bob's masscenter is found with:
+
+    >>> lower_bob.masscenter.pos_from(ceiling.masscenter)
+    l1*U_frame.x + l2*L_frame.x
+
+    The angular velocities of the two pendulum links can be computed with
+    respect to the ceiling.
+
+    >>> upper_bob.frame.ang_vel_in(ceiling.frame)
+    u_P1(t)*C_frame.z
+    >>> lower_bob.frame.ang_vel_in(ceiling.frame)
+    u_P1(t)*C_frame.z + u_P2(t)*U_frame.z
+
+    And finally, the linear velocities of the two pendulum bobs can be computed
+    with respect to the ceiling.
+
+    >>> upper_bob.masscenter.vel(ceiling.frame)
+    l1*u_P1(t)*U_frame.y
+    >>> lower_bob.masscenter.vel(ceiling.frame)
+    l1*u_P1(t)*U_frame.y + l2*(u_P1(t) + u_P2(t))*L_frame.y
+
+    """
+
+    def __init__(self, name, parent, child, coordinates=None, speeds=None,
+                 parent_point=None, child_point=None, parent_axis=None,
+                 child_axis=None, parent_interframe=None, child_interframe=None,
+                 joint_axis=None, parent_joint_pos=None, child_joint_pos=None):
+
+        self._joint_axis = joint_axis
+        super().__init__(name, parent, child, coordinates, speeds, parent_point,
+                         child_point, parent_axis, child_axis,
+                         parent_interframe, child_interframe, parent_joint_pos,
+                         child_joint_pos)
+
+    def __str__(self):
+        return (f'PinJoint: {self.name}  parent: {self.parent}  '
+                f'child: {self.child}')
+
+    @property
+    def joint_axis(self):
+        """Axis about which the child rotates with respect to the parent."""
+        return self._joint_axis
+
+    def _generate_coordinates(self, coordinate):
+        return self._fill_coordinate_list(coordinate, 1, 'q')
+
+    def _generate_speeds(self, speed):
+        return self._fill_coordinate_list(speed, 1, 'u')
+
+    def _orient_frames(self):
+        self._joint_axis = self._axis(self.joint_axis, self.parent_interframe)
+        self.child_interframe.orient_axis(
+            self.parent_interframe, self.joint_axis, self.coordinates[0])
+
+    def _set_angular_velocity(self):
+        self.child_interframe.set_ang_vel(self.parent_interframe, self.speeds[
+            0] * self.joint_axis.normalize())
+
+    def _set_linear_velocity(self):
+        self.child_point.set_pos(self.parent_point, 0)
+        self.parent_point.set_vel(self.parent.frame, 0)
+        self.child_point.set_vel(self.child.frame, 0)
+        self.child.masscenter.v2pt_theory(self.parent_point,
+                                          self.parent.frame, self.child.frame)
+
+
+class PrismaticJoint(Joint):
+    """Prismatic (Sliding) Joint.
+
+    .. image:: PrismaticJoint.svg
+
+    Explanation
+    ===========
+
+    It is defined such that the child body translates with respect to the parent
+    body along the body-fixed joint axis. The location of the joint is defined
+    by two points, one in each body, which coincide when the generalized
+    coordinate is zero. The direction cosine matrix between the
+    parent_interframe and child_interframe is the identity matrix. Therefore,
+    the direction cosine matrix between the parent and child frames is fully
+    defined by the definition of the intermediate frames. The page on the joints
+    framework gives a more detailed explanation of the intermediate frames.
+
+    Parameters
+    ==========
+
+    name : string
+        A unique name for the joint.
+    parent : Body
+        The parent body of joint.
+    child : Body
+        The child body of joint.
+    coordinates : dynamicsymbol, optional
+        Generalized coordinates of the joint. The default value is
+        ``dynamicsymbols(f'q_{joint.name}')``.
+    speeds : dynamicsymbol, optional
+        Generalized speeds of joint. The default value is
+        ``dynamicsymbols(f'u_{joint.name}')``.
+    parent_point : Point or Vector, optional
+        Attachment point where the joint is fixed to the parent body. If a
+        vector is provided, then the attachment point is computed by adding the
+        vector to the body's mass center. The default value is the parent's mass
+        center.
+    child_point : Point or Vector, optional
+        Attachment point where the joint is fixed to the child body. If a
+        vector is provided, then the attachment point is computed by adding the
+        vector to the body's mass center. The default value is the child's mass
+        center.
+    parent_axis : Vector, optional
+        .. deprecated:: 1.12
+            Axis fixed in the parent body which aligns with an axis fixed in the
+            child body. The default is the x axis of parent's reference frame.
+            For more information on this deprecation, see
+            :ref:`deprecated-mechanics-joint-axis`.
+    child_axis : Vector, optional
+        .. deprecated:: 1.12
+            Axis fixed in the child body which aligns with an axis fixed in the
+            parent body. The default is the x axis of child's reference frame.
+            For more information on this deprecation, see
+            :ref:`deprecated-mechanics-joint-axis`.
+    parent_interframe : ReferenceFrame, optional
+        Intermediate frame of the parent body with respect to which the joint
+        transformation is formulated. If a Vector is provided then an interframe
+        is created which aligns its X axis with the given vector. The default
+        value is the parent's own frame.
+    child_interframe : ReferenceFrame, optional
+        Intermediate frame of the child body with respect to which the joint
+        transformation is formulated. If a Vector is provided then an interframe
+        is created which aligns its X axis with the given vector. The default
+        value is the child's own frame.
+    joint_axis : Vector
+        The axis along which the translation occurs. Note that the components
+        of this axis are the same in the parent_interframe and child_interframe.
+    parent_joint_pos : Point or Vector, optional
+        .. deprecated:: 1.12
+            This argument is replaced by parent_point and will be removed in a
+            future version.
+            See :ref:`deprecated-mechanics-joint-pos` for more information.
+    child_joint_pos : Point or Vector, optional
+        .. deprecated:: 1.12
+            This argument is replaced by child_point and will be removed in a
+            future version.
+            See :ref:`deprecated-mechanics-joint-pos` for more information.
+
+    Attributes
+    ==========
+
+    name : string
+        The joint's name.
+    parent : Body
+        The joint's parent body.
+    child : Body
+        The joint's child body.
+    coordinates : Matrix
+        Matrix of the joint's generalized coordinates.
+    speeds : Matrix
+        Matrix of the joint's generalized speeds.
+    parent_point : Point
+        Attachment point where the joint is fixed to the parent body.
+    child_point : Point
+        Attachment point where the joint is fixed to the child body.
+    parent_axis : Vector
+        The axis fixed in the parent frame that represents the joint.
+    child_axis : Vector
+        The axis fixed in the child frame that represents the joint.
+    parent_interframe : ReferenceFrame
+        Intermediate frame of the parent body with respect to which the joint
+        transformation is formulated.
+    child_interframe : ReferenceFrame
+        Intermediate frame of the child body with respect to which the joint
+        transformation is formulated.
+    kdes : Matrix
+        Kinematical differential equations of the joint.
+
+    Examples
+    =========
+
+    A single prismatic joint is created from two bodies and has the following
+    basic attributes:
+
+    >>> from sympy.physics.mechanics import Body, PrismaticJoint
+    >>> parent = Body('P')
+    >>> parent
+    P
+    >>> child = Body('C')
+    >>> child
+    C
+    >>> joint = PrismaticJoint('PC', parent, child)
+    >>> joint
+    PrismaticJoint: PC  parent: P  child: C
+    >>> joint.name
+    'PC'
+    >>> joint.parent
+    P
+    >>> joint.child
+    C
+    >>> joint.parent_point
+    P_masscenter
+    >>> joint.child_point
+    C_masscenter
+    >>> joint.parent_axis
+    P_frame.x
+    >>> joint.child_axis
+    C_frame.x
+    >>> joint.coordinates
+    Matrix([[q_PC(t)]])
+    >>> joint.speeds
+    Matrix([[u_PC(t)]])
+    >>> joint.child.frame.ang_vel_in(joint.parent.frame)
+    0
+    >>> joint.child.frame.dcm(joint.parent.frame)
+    Matrix([
+    [1, 0, 0],
+    [0, 1, 0],
+    [0, 0, 1]])
+    >>> joint.child_point.pos_from(joint.parent_point)
+    q_PC(t)*P_frame.x
+
+    To further demonstrate the use of the prismatic joint, the kinematics of two
+    masses sliding, one moving relative to a fixed body and the other relative
+    to the moving body. about the X axis of each connected body can be created
+    as follows.
+
+    >>> from sympy.physics.mechanics import PrismaticJoint, Body
+
+    First create bodies to represent the fixed ceiling and one to represent
+    a particle.
+
+    >>> wall = Body('W')
+    >>> Part1 = Body('P1')
+    >>> Part2 = Body('P2')
+
+    The first joint will connect the particle to the ceiling and the
+    joint axis will be about the X axis for each body.
+
+    >>> J1 = PrismaticJoint('J1', wall, Part1)
+
+    The second joint will connect the second particle to the first particle
+    and the joint axis will also be about the X axis for each body.
+
+    >>> J2 = PrismaticJoint('J2', Part1, Part2)
+
+    Once the joint is established the kinematics of the connected bodies can
+    be accessed. First the direction cosine matrices of Part relative
+    to the ceiling are found:
+
+    >>> Part1.dcm(wall)
+    Matrix([
+    [1, 0, 0],
+    [0, 1, 0],
+    [0, 0, 1]])
+
+    >>> Part2.dcm(wall)
+    Matrix([
+    [1, 0, 0],
+    [0, 1, 0],
+    [0, 0, 1]])
+
+    The position of the particles' masscenter is found with:
+
+    >>> Part1.masscenter.pos_from(wall.masscenter)
+    q_J1(t)*W_frame.x
+
+    >>> Part2.masscenter.pos_from(wall.masscenter)
+    q_J1(t)*W_frame.x + q_J2(t)*P1_frame.x
+
+    The angular velocities of the two particle links can be computed with
+    respect to the ceiling.
+
+    >>> Part1.ang_vel_in(wall)
+    0
+
+    >>> Part2.ang_vel_in(wall)
+    0
+
+    And finally, the linear velocities of the two particles can be computed
+    with respect to the ceiling.
+
+    >>> Part1.masscenter_vel(wall)
+    u_J1(t)*W_frame.x
+
+    >>> Part2.masscenter.vel(wall.frame)
+    u_J1(t)*W_frame.x + Derivative(q_J2(t), t)*P1_frame.x
+
+    """
+
+    def __init__(self, name, parent, child, coordinates=None, speeds=None,
+                 parent_point=None, child_point=None, parent_axis=None,
+                 child_axis=None, parent_interframe=None, child_interframe=None,
+                 joint_axis=None, parent_joint_pos=None, child_joint_pos=None):
+
+        self._joint_axis = joint_axis
+        super().__init__(name, parent, child, coordinates, speeds, parent_point,
+                         child_point, parent_axis, child_axis,
+                         parent_interframe, child_interframe, parent_joint_pos,
+                         child_joint_pos)
+
+    def __str__(self):
+        return (f'PrismaticJoint: {self.name}  parent: {self.parent}  '
+                f'child: {self.child}')
+
+    @property
+    def joint_axis(self):
+        """Axis along which the child translates with respect to the parent."""
+        return self._joint_axis
+
+    def _generate_coordinates(self, coordinate):
+        return self._fill_coordinate_list(coordinate, 1, 'q')
+
+    def _generate_speeds(self, speed):
+        return self._fill_coordinate_list(speed, 1, 'u')
+
+    def _orient_frames(self):
+        self._joint_axis = self._axis(self.joint_axis, self.parent_interframe)
+        self.child_interframe.orient_axis(
+            self.parent_interframe, self.joint_axis, 0)
+
+    def _set_angular_velocity(self):
+        self.child_interframe.set_ang_vel(self.parent_interframe, 0)
+
+    def _set_linear_velocity(self):
+        axis = self.joint_axis.normalize()
+        self.child_point.set_pos(self.parent_point, self.coordinates[0] * axis)
+        self.parent_point.set_vel(self.parent.frame, 0)
+        self.child_point.set_vel(self.child.frame, 0)
+        self.child_point.set_vel(self.parent.frame, self.speeds[0] * axis)
+        self.child.masscenter.set_vel(self.parent.frame, self.speeds[0] * axis)
+
+
+class CylindricalJoint(Joint):
+    """Cylindrical Joint.
+
+    .. image:: CylindricalJoint.svg
+        :align: center
+        :width: 600
+
+    Explanation
+    ===========
+
+    A cylindrical joint is defined such that the child body both rotates about
+    and translates along the body-fixed joint axis with respect to the parent
+    body. The joint axis is both the rotation axis and translation axis. The
+    location of the joint is defined by two points, one in each body, which
+    coincide when the generalized coordinate corresponding to the translation is
+    zero. The direction cosine matrix between the child interframe and parent
+    interframe is formed using a simple rotation about the joint axis. The page
+    on the joints framework gives a more detailed explanation of the
+    intermediate frames.
+
+    Parameters
+    ==========
+
+    name : string
+        A unique name for the joint.
+    parent : Body
+        The parent body of joint.
+    child : Body
+        The child body of joint.
+    rotation_coordinate : dynamicsymbol, optional
+        Generalized coordinate corresponding to the rotation angle. The default
+        value is ``dynamicsymbols(f'q0_{joint.name}')``.
+    translation_coordinate : dynamicsymbol, optional
+        Generalized coordinate corresponding to the translation distance. The
+        default value is ``dynamicsymbols(f'q1_{joint.name}')``.
+    rotation_speed : dynamicsymbol, optional
+        Generalized speed corresponding to the angular velocity. The default
+        value is ``dynamicsymbols(f'u0_{joint.name}')``.
+    translation_speed : dynamicsymbol, optional
+        Generalized speed corresponding to the translation velocity. The default
+        value is ``dynamicsymbols(f'u1_{joint.name}')``.
+    parent_point : Point or Vector, optional
+        Attachment point where the joint is fixed to the parent body. If a
+        vector is provided, then the attachment point is computed by adding the
+        vector to the body's mass center. The default value is the parent's mass
+        center.
+    child_point : Point or Vector, optional
+        Attachment point where the joint is fixed to the child body. If a
+        vector is provided, then the attachment point is computed by adding the
+        vector to the body's mass center. The default value is the child's mass
+        center.
+    parent_interframe : ReferenceFrame, optional
+        Intermediate frame of the parent body with respect to which the joint
+        transformation is formulated. If a Vector is provided then an interframe
+        is created which aligns its X axis with the given vector. The default
+        value is the parent's own frame.
+    child_interframe : ReferenceFrame, optional
+        Intermediate frame of the child body with respect to which the joint
+        transformation is formulated. If a Vector is provided then an interframe
+        is created which aligns its X axis with the given vector. The default
+        value is the child's own frame.
+    joint_axis : Vector, optional
+        The rotation as well as translation axis. Note that the components of
+        this axis are the same in the parent_interframe and child_interframe.
+
+    Attributes
+    ==========
+
+    name : string
+        The joint's name.
+    parent : Body
+        The joint's parent body.
+    child : Body
+        The joint's child body.
+    rotation_coordinate : dynamicsymbol
+        Generalized coordinate corresponding to the rotation angle.
+    translation_coordinate : dynamicsymbol
+        Generalized coordinate corresponding to the translation distance.
+    rotation_speed : dynamicsymbol
+        Generalized speed corresponding to the angular velocity.
+    translation_speed : dynamicsymbol
+        Generalized speed corresponding to the translation velocity.
+    coordinates : Matrix
+        Matrix of the joint's generalized coordinates.
+    speeds : Matrix
+        Matrix of the joint's generalized speeds.
+    parent_point : Point
+        Attachment point where the joint is fixed to the parent body.
+    child_point : Point
+        Attachment point where the joint is fixed to the child body.
+    parent_interframe : ReferenceFrame
+        Intermediate frame of the parent body with respect to which the joint
+        transformation is formulated.
+    child_interframe : ReferenceFrame
+        Intermediate frame of the child body with respect to which the joint
+        transformation is formulated.
+    kdes : Matrix
+        Kinematical differential equations of the joint.
+    joint_axis : Vector
+        The axis of rotation and translation.
+
+    Examples
+    =========
+
+    A single cylindrical joint is created between two bodies and has the
+    following basic attributes:
+
+    >>> from sympy.physics.mechanics import Body, CylindricalJoint
+    >>> parent = Body('P')
+    >>> parent
+    P
+    >>> child = Body('C')
+    >>> child
+    C
+    >>> joint = CylindricalJoint('PC', parent, child)
+    >>> joint
+    CylindricalJoint: PC  parent: P  child: C
+    >>> joint.name
+    'PC'
+    >>> joint.parent
+    P
+    >>> joint.child
+    C
+    >>> joint.parent_point
+    P_masscenter
+    >>> joint.child_point
+    C_masscenter
+    >>> joint.parent_axis
+    P_frame.x
+    >>> joint.child_axis
+    C_frame.x
+    >>> joint.coordinates
+    Matrix([
+    [q0_PC(t)],
+    [q1_PC(t)]])
+    >>> joint.speeds
+    Matrix([
+    [u0_PC(t)],
+    [u1_PC(t)]])
+    >>> joint.child.frame.ang_vel_in(joint.parent.frame)
+    u0_PC(t)*P_frame.x
+    >>> joint.child.frame.dcm(joint.parent.frame)
+    Matrix([
+    [1,              0,             0],
+    [0,  cos(q0_PC(t)), sin(q0_PC(t))],
+    [0, -sin(q0_PC(t)), cos(q0_PC(t))]])
+    >>> joint.child_point.pos_from(joint.parent_point)
+    q1_PC(t)*P_frame.x
+    >>> child.masscenter.vel(parent.frame)
+    u1_PC(t)*P_frame.x
+
+    To further demonstrate the use of the cylindrical joint, the kinematics of
+    two cylindrical joints perpendicular to each other can be created as follows.
+
+    >>> from sympy import symbols
+    >>> from sympy.physics.mechanics import Body, CylindricalJoint
+    >>> r, l, w = symbols('r l w')
+
+    First create bodies to represent the fixed floor with a fixed pole on it.
+    The second body represents a freely moving tube around that pole. The third
+    body represents a solid flag freely translating along and rotating around
+    the Y axis of the tube.
+
+    >>> floor = Body('floor')
+    >>> tube = Body('tube')
+    >>> flag = Body('flag')
+
+    The first joint will connect the first tube to the floor with it translating
+    along and rotating around the Z axis of both bodies.
+
+    >>> floor_joint = CylindricalJoint('C1', floor, tube, joint_axis=floor.z)
+
+    The second joint will connect the tube perpendicular to the flag along the Y
+    axis of both the tube and the flag, with the joint located at a distance
+    ``r`` from the tube's center of mass and a combination of the distances
+    ``l`` and ``w`` from the flag's center of mass.
+
+    >>> flag_joint = CylindricalJoint('C2', tube, flag,
+    ...                               parent_point=r * tube.y,
+    ...                               child_point=-w * flag.y + l * flag.z,
+    ...                               joint_axis=tube.y)
+
+    Once the joints are established the kinematics of the connected bodies can
+    be accessed. First the direction cosine matrices of both the body and the
+    flag relative to the floor are found:
+
+    >>> tube.dcm(floor)
+    Matrix([
+    [ cos(q0_C1(t)), sin(q0_C1(t)), 0],
+    [-sin(q0_C1(t)), cos(q0_C1(t)), 0],
+    [             0,             0, 1]])
+    >>> flag.dcm(floor)
+    Matrix([
+    [cos(q0_C1(t))*cos(q0_C2(t)), sin(q0_C1(t))*cos(q0_C2(t)), -sin(q0_C2(t))],
+    [             -sin(q0_C1(t)),               cos(q0_C1(t)),              0],
+    [sin(q0_C2(t))*cos(q0_C1(t)), sin(q0_C1(t))*sin(q0_C2(t)),  cos(q0_C2(t))]])
+
+    The position of the flag's center of mass is found with:
+
+    >>> flag.masscenter.pos_from(floor.masscenter)
+    q1_C1(t)*floor_frame.z + (r + q1_C2(t))*tube_frame.y + w*flag_frame.y - l*flag_frame.z
+
+    The angular velocities of the two tubes can be computed with respect to the
+    floor.
+
+    >>> tube.ang_vel_in(floor)
+    u0_C1(t)*floor_frame.z
+    >>> flag.ang_vel_in(floor)
+    u0_C1(t)*floor_frame.z + u0_C2(t)*tube_frame.y
+
+    Finally, the linear velocities of the two tube centers of mass can be
+    computed with respect to the floor, while expressed in the tube's frame.
+
+    >>> tube.masscenter.vel(floor.frame).to_matrix(tube.frame)
+    Matrix([
+    [       0],
+    [       0],
+    [u1_C1(t)]])
+    >>> flag.masscenter.vel(floor.frame).to_matrix(tube.frame).simplify()
+    Matrix([
+    [-l*u0_C2(t)*cos(q0_C2(t)) - r*u0_C1(t) - w*u0_C1(t) - q1_C2(t)*u0_C1(t)],
+    [                    -l*u0_C1(t)*sin(q0_C2(t)) + Derivative(q1_C2(t), t)],
+    [                                    l*u0_C2(t)*sin(q0_C2(t)) + u1_C1(t)]])
+
+    """
+
+    def __init__(self, name, parent, child, rotation_coordinate=None,
+                 translation_coordinate=None, rotation_speed=None,
+                 translation_speed=None, parent_point=None, child_point=None,
+                 parent_interframe=None, child_interframe=None,
+                 joint_axis=None):
+        self._joint_axis = joint_axis
+        coordinates = (rotation_coordinate, translation_coordinate)
+        speeds = (rotation_speed, translation_speed)
+        super().__init__(name, parent, child, coordinates, speeds,
+                         parent_point, child_point,
+                         parent_interframe=parent_interframe,
+                         child_interframe=child_interframe)
+
+    def __str__(self):
+        return (f'CylindricalJoint: {self.name}  parent: {self.parent}  '
+                f'child: {self.child}')
+
+    @property
+    def joint_axis(self):
+        """Axis about and along which the rotation and translation occurs."""
+        return self._joint_axis
+
+    @property
+    def rotation_coordinate(self):
+        """Generalized coordinate corresponding to the rotation angle."""
+        return self.coordinates[0]
+
+    @property
+    def translation_coordinate(self):
+        """Generalized coordinate corresponding to the translation distance."""
+        return self.coordinates[1]
+
+    @property
+    def rotation_speed(self):
+        """Generalized speed corresponding to the angular velocity."""
+        return self.speeds[0]
+
+    @property
+    def translation_speed(self):
+        """Generalized speed corresponding to the translation velocity."""
+        return self.speeds[1]
+
+    def _generate_coordinates(self, coordinates):
+        return self._fill_coordinate_list(coordinates, 2, 'q')
+
+    def _generate_speeds(self, speeds):
+        return self._fill_coordinate_list(speeds, 2, 'u')
+
+    def _orient_frames(self):
+        self._joint_axis = self._axis(self.joint_axis, self.parent_interframe)
+        self.child_interframe.orient_axis(
+            self.parent_interframe, self.joint_axis, self.rotation_coordinate)
+
+    def _set_angular_velocity(self):
+        self.child_interframe.set_ang_vel(
+            self.parent_interframe,
+            self.rotation_speed * self.joint_axis.normalize())
+
+    def _set_linear_velocity(self):
+        self.child_point.set_pos(
+            self.parent_point,
+            self.translation_coordinate * self.joint_axis.normalize())
+        self.parent_point.set_vel(self.parent.frame, 0)
+        self.child_point.set_vel(self.child.frame, 0)
+        self.child_point.set_vel(
+            self.parent.frame,
+            self.translation_speed * self.joint_axis.normalize())
+        self.child.masscenter.v2pt_theory(self.child_point, self.parent.frame,
+                                          self.child_interframe)
+
+
+class PlanarJoint(Joint):
+    """Planar Joint.
+
+    .. image:: PlanarJoint.svg
+        :align: center
+        :width: 800
+
+    Explanation
+    ===========
+
+    A planar joint is defined such that the child body translates over a fixed
+    plane of the parent body as well as rotate about the rotation axis, which
+    is perpendicular to that plane. The origin of this plane is the
+    ``parent_point`` and the plane is spanned by two nonparallel planar vectors.
+    The location of the ``child_point`` is based on the planar vectors
+    ($\\vec{v}_1$, $\\vec{v}_2$) and generalized coordinates ($q_1$, $q_2$),
+    i.e. $\\vec{r} = q_1 \\hat{v}_1 + q_2 \\hat{v}_2$. The direction cosine
+    matrix between the ``child_interframe`` and ``parent_interframe`` is formed
+    using a simple rotation ($q_0$) about the rotation axis.
+
+    In order to simplify the definition of the ``PlanarJoint``, the
+    ``rotation_axis`` and ``planar_vectors`` are set to be the unit vectors of
+    the ``parent_interframe`` according to the table below. This ensures that
+    you can only define these vectors by creating a separate frame and supplying
+    that as the interframe. If you however would only like to supply the normals
+    of the plane with respect to the parent and child bodies, then you can also
+    supply those to the ``parent_interframe`` and ``child_interframe``
+    arguments. An example of both of these cases is in the examples section
+    below and the page on the joints framework provides a more detailed
+    explanation of the intermediate frames.
+
+    .. list-table::
+
+        * - ``rotation_axis``
+          - ``parent_interframe.x``
+        * - ``planar_vectors[0]``
+          - ``parent_interframe.y``
+        * - ``planar_vectors[1]``
+          - ``parent_interframe.z``
+
+    Parameters
+    ==========
+
+    name : string
+        A unique name for the joint.
+    parent : Body
+        The parent body of joint.
+    child : Body
+        The child body of joint.
+    rotation_coordinate : dynamicsymbol, optional
+        Generalized coordinate corresponding to the rotation angle. The default
+        value is ``dynamicsymbols(f'q0_{joint.name}')``.
+    planar_coordinates : iterable of dynamicsymbols, optional
+        Two generalized coordinates used for the planar translation. The default
+        value is ``dynamicsymbols(f'q1_{joint.name} q2_{joint.name}')``.
+    rotation_speed : dynamicsymbol, optional
+        Generalized speed corresponding to the angular velocity. The default
+        value is ``dynamicsymbols(f'u0_{joint.name}')``.
+    planar_speeds : dynamicsymbols, optional
+        Two generalized speeds used for the planar translation velocity. The
+        default value is ``dynamicsymbols(f'u1_{joint.name} u2_{joint.name}')``.
+    parent_point : Point or Vector, optional
+        Attachment point where the joint is fixed to the parent body. If a
+        vector is provided, then the attachment point is computed by adding the
+        vector to the body's mass center. The default value is the parent's mass
+        center.
+    child_point : Point or Vector, optional
+        Attachment point where the joint is fixed to the child body. If a
+        vector is provided, then the attachment point is computed by adding the
+        vector to the body's mass center. The default value is the child's mass
+        center.
+    parent_interframe : ReferenceFrame, optional
+        Intermediate frame of the parent body with respect to which the joint
+        transformation is formulated. If a Vector is provided then an interframe
+        is created which aligns its X axis with the given vector. The default
+        value is the parent's own frame.
+    child_interframe : ReferenceFrame, optional
+        Intermediate frame of the child body with respect to which the joint
+        transformation is formulated. If a Vector is provided then an interframe
+        is created which aligns its X axis with the given vector. The default
+        value is the child's own frame.
+
+    Attributes
+    ==========
+
+    name : string
+        The joint's name.
+    parent : Body
+        The joint's parent body.
+    child : Body
+        The joint's child body.
+    rotation_coordinate : dynamicsymbol
+        Generalized coordinate corresponding to the rotation angle.
+    planar_coordinates : Matrix
+        Two generalized coordinates used for the planar translation.
+    rotation_speed : dynamicsymbol
+        Generalized speed corresponding to the angular velocity.
+    planar_speeds : Matrix
+        Two generalized speeds used for the planar translation velocity.
+    coordinates : Matrix
+        Matrix of the joint's generalized coordinates.
+    speeds : Matrix
+        Matrix of the joint's generalized speeds.
+    parent_point : Point
+        Attachment point where the joint is fixed to the parent body.
+    child_point : Point
+        Attachment point where the joint is fixed to the child body.
+    parent_interframe : ReferenceFrame
+        Intermediate frame of the parent body with respect to which the joint
+        transformation is formulated.
+    child_interframe : ReferenceFrame
+        Intermediate frame of the child body with respect to which the joint
+        transformation is formulated.
+    kdes : Matrix
+        Kinematical differential equations of the joint.
+    rotation_axis : Vector
+        The axis about which the rotation occurs.
+    planar_vectors : list
+        The vectors that describe the planar translation directions.
+
+    Examples
+    =========
+
+    A single planar joint is created between two bodies and has the following
+    basic attributes:
+
+    >>> from sympy.physics.mechanics import Body, PlanarJoint
+    >>> parent = Body('P')
+    >>> parent
+    P
+    >>> child = Body('C')
+    >>> child
+    C
+    >>> joint = PlanarJoint('PC', parent, child)
+    >>> joint
+    PlanarJoint: PC  parent: P  child: C
+    >>> joint.name
+    'PC'
+    >>> joint.parent
+    P
+    >>> joint.child
+    C
+    >>> joint.parent_point
+    P_masscenter
+    >>> joint.child_point
+    C_masscenter
+    >>> joint.rotation_axis
+    P_frame.x
+    >>> joint.planar_vectors
+    [P_frame.y, P_frame.z]
+    >>> joint.rotation_coordinate
+    q0_PC(t)
+    >>> joint.planar_coordinates
+    Matrix([
+    [q1_PC(t)],
+    [q2_PC(t)]])
+    >>> joint.coordinates
+    Matrix([
+    [q0_PC(t)],
+    [q1_PC(t)],
+    [q2_PC(t)]])
+    >>> joint.rotation_speed
+    u0_PC(t)
+    >>> joint.planar_speeds
+    Matrix([
+    [u1_PC(t)],
+    [u2_PC(t)]])
+    >>> joint.speeds
+    Matrix([
+    [u0_PC(t)],
+    [u1_PC(t)],
+    [u2_PC(t)]])
+    >>> joint.child.frame.ang_vel_in(joint.parent.frame)
+    u0_PC(t)*P_frame.x
+    >>> joint.child.frame.dcm(joint.parent.frame)
+    Matrix([
+    [1,              0,             0],
+    [0,  cos(q0_PC(t)), sin(q0_PC(t))],
+    [0, -sin(q0_PC(t)), cos(q0_PC(t))]])
+    >>> joint.child_point.pos_from(joint.parent_point)
+    q1_PC(t)*P_frame.y + q2_PC(t)*P_frame.z
+    >>> child.masscenter.vel(parent.frame)
+    u1_PC(t)*P_frame.y + u2_PC(t)*P_frame.z
+
+    To further demonstrate the use of the planar joint, the kinematics of a
+    block sliding on a slope, can be created as follows.
+
+    >>> from sympy import symbols
+    >>> from sympy.physics.mechanics import PlanarJoint, Body, ReferenceFrame
+    >>> a, d, h = symbols('a d h')
+
+    First create bodies to represent the slope and the block.
+
+    >>> ground = Body('G')
+    >>> block = Body('B')
+
+    To define the slope you can either define the plane by specifying the
+    ``planar_vectors`` or/and the ``rotation_axis``. However it is advisable to
+    create a rotated intermediate frame, so that the ``parent_vectors`` and
+    ``rotation_axis`` will be the unit vectors of this intermediate frame.
+
+    >>> slope = ReferenceFrame('A')
+    >>> slope.orient_axis(ground.frame, ground.y, a)
+
+    The planar joint can be created using these bodies and intermediate frame.
+    We can specify the origin of the slope to be ``d`` above the slope's center
+    of mass and the block's center of mass to be a distance ``h`` above the
+    slope's surface. Note that we can specify the normal of the plane using the
+    rotation axis argument.
+
+    >>> joint = PlanarJoint('PC', ground, block, parent_point=d * ground.x,
+    ...                     child_point=-h * block.x, parent_interframe=slope)
+
+    Once the joint is established the kinematics of the bodies can be accessed.
+    First the ``rotation_axis``, which is normal to the plane and the
+    ``plane_vectors``, can be found.
+
+    >>> joint.rotation_axis
+    A.x
+    >>> joint.planar_vectors
+    [A.y, A.z]
+
+    The direction cosine matrix of the block with respect to the ground can be
+    found with:
+
+    >>> block.dcm(ground)
+    Matrix([
+    [              cos(a),              0,              -sin(a)],
+    [sin(a)*sin(q0_PC(t)),  cos(q0_PC(t)), sin(q0_PC(t))*cos(a)],
+    [sin(a)*cos(q0_PC(t)), -sin(q0_PC(t)), cos(a)*cos(q0_PC(t))]])
+
+    The angular velocity of the block can be computed with respect to the
+    ground.
+
+    >>> block.ang_vel_in(ground)
+    u0_PC(t)*A.x
+
+    The position of the block's center of mass can be found with:
+
+    >>> block.masscenter.pos_from(ground.masscenter)
+    d*G_frame.x + h*B_frame.x + q1_PC(t)*A.y + q2_PC(t)*A.z
+
+    Finally, the linear velocity of the block's center of mass can be
+    computed with respect to the ground.
+
+    >>> block.masscenter.vel(ground.frame)
+    u1_PC(t)*A.y + u2_PC(t)*A.z
+
+    In some cases it could be your preference to only define the normals of the
+    plane with respect to both bodies. This can most easily be done by supplying
+    vectors to the ``interframe`` arguments. What will happen in this case is
+    that an interframe will be created with its ``x`` axis aligned with the
+    provided vector. For a further explanation of how this is done see the notes
+    of the ``Joint`` class. In the code below, the above example (with the block
+    on the slope) is recreated by supplying vectors to the interframe arguments.
+    Note that the previously described option is however more computationally
+    efficient, because the algorithm now has to compute the rotation angle
+    between the provided vector and the 'x' axis.
+
+    >>> from sympy import symbols, cos, sin
+    >>> from sympy.physics.mechanics import PlanarJoint, Body
+    >>> a, d, h = symbols('a d h')
+    >>> ground = Body('G')
+    >>> block = Body('B')
+    >>> joint = PlanarJoint(
+    ...     'PC', ground, block, parent_point=d * ground.x,
+    ...     child_point=-h * block.x, child_interframe=block.x,
+    ...     parent_interframe=cos(a) * ground.x + sin(a) * ground.z)
+    >>> block.dcm(ground).simplify()
+    Matrix([
+    [               cos(a),              0,               sin(a)],
+    [-sin(a)*sin(q0_PC(t)),  cos(q0_PC(t)), sin(q0_PC(t))*cos(a)],
+    [-sin(a)*cos(q0_PC(t)), -sin(q0_PC(t)), cos(a)*cos(q0_PC(t))]])
+
+    """
+
+    def __init__(self, name, parent, child, rotation_coordinate=None,
+                 planar_coordinates=None, rotation_speed=None,
+                 planar_speeds=None, parent_point=None, child_point=None,
+                 parent_interframe=None, child_interframe=None):
+        # A ready to merge implementation of setting the planar_vectors and
+        # rotation_axis was added and removed in PR #24046
+        coordinates = (rotation_coordinate, planar_coordinates)
+        speeds = (rotation_speed, planar_speeds)
+        super().__init__(name, parent, child, coordinates, speeds,
+                         parent_point, child_point,
+                         parent_interframe=parent_interframe,
+                         child_interframe=child_interframe)
+
+    def __str__(self):
+        return (f'PlanarJoint: {self.name}  parent: {self.parent}  '
+                f'child: {self.child}')
+
+    @property
+    def rotation_coordinate(self):
+        """Generalized coordinate corresponding to the rotation angle."""
+        return self.coordinates[0]
+
+    @property
+    def planar_coordinates(self):
+        """Two generalized coordinates used for the planar translation."""
+        return self.coordinates[1:, 0]
+
+    @property
+    def rotation_speed(self):
+        """Generalized speed corresponding to the angular velocity."""
+        return self.speeds[0]
+
+    @property
+    def planar_speeds(self):
+        """Two generalized speeds used for the planar translation velocity."""
+        return self.speeds[1:, 0]
+
+    @property
+    def rotation_axis(self):
+        """The axis about which the rotation occurs."""
+        return self.parent_interframe.x
+
+    @property
+    def planar_vectors(self):
+        """The vectors that describe the planar translation directions."""
+        return [self.parent_interframe.y, self.parent_interframe.z]
+
+    def _generate_coordinates(self, coordinates):
+        rotation_speed = self._fill_coordinate_list(coordinates[0], 1, 'q',
+                                                    number_single=True)
+        planar_speeds = self._fill_coordinate_list(coordinates[1], 2, 'q', 1)
+        return rotation_speed.col_join(planar_speeds)
+
+    def _generate_speeds(self, speeds):
+        rotation_speed = self._fill_coordinate_list(speeds[0], 1, 'u',
+                                                    number_single=True)
+        planar_speeds = self._fill_coordinate_list(speeds[1], 2, 'u', 1)
+        return rotation_speed.col_join(planar_speeds)
+
+    def _orient_frames(self):
+        self.child_interframe.orient_axis(
+            self.parent_interframe, self.rotation_axis,
+            self.rotation_coordinate)
+
+    def _set_angular_velocity(self):
+        self.child_interframe.set_ang_vel(
+            self.parent_interframe,
+            self.rotation_speed * self.rotation_axis)
+
+    def _set_linear_velocity(self):
+        self.child_point.set_pos(
+            self.parent_point,
+            self.planar_coordinates[0] * self.planar_vectors[0] +
+            self.planar_coordinates[1] * self.planar_vectors[1])
+        self.parent_point.set_vel(self.parent_interframe, 0)
+        self.child_point.set_vel(self.child_interframe, 0)
+        self.child_point.set_vel(
+            self.parent.frame, self.planar_speeds[0] * self.planar_vectors[0] +
+            self.planar_speeds[1] * self.planar_vectors[1])
+        self.child.masscenter.v2pt_theory(self.child_point, self.parent.frame,
+                                          self.child.frame)
+
+
+class SphericalJoint(Joint):
+    """Spherical (Ball-and-Socket) Joint.
+
+    .. image:: SphericalJoint.svg
+        :align: center
+        :width: 600
+
+    Explanation
+    ===========
+
+    A spherical joint is defined such that the child body is free to rotate in
+    any direction, without allowing a translation of the ``child_point``. As can
+    also be seen in the image, the ``parent_point`` and ``child_point`` are
+    fixed on top of each other, i.e. the ``joint_point``. This rotation is
+    defined using the :func:`parent_interframe.orient(child_interframe,
+    rot_type, amounts, rot_order)
+    <sympy.physics.vector.frame.ReferenceFrame.orient>` method. The default
+    rotation consists of three relative rotations, i.e. body-fixed rotations.
+    Based on the direction cosine matrix following from these rotations, the
+    angular velocity is computed based on the generalized coordinates and
+    generalized speeds.
+
+    Parameters
+    ==========
+
+    name : string
+        A unique name for the joint.
+    parent : Body
+        The parent body of joint.
+    child : Body
+        The child body of joint.
+    coordinates: iterable of dynamicsymbols, optional
+        Generalized coordinates of the joint.
+    speeds : iterable of dynamicsymbols, optional
+        Generalized speeds of joint.
+    parent_point : Point or Vector, optional
+        Attachment point where the joint is fixed to the parent body. If a
+        vector is provided, then the attachment point is computed by adding the
+        vector to the body's mass center. The default value is the parent's mass
+        center.
+    child_point : Point or Vector, optional
+        Attachment point where the joint is fixed to the child body. If a
+        vector is provided, then the attachment point is computed by adding the
+        vector to the body's mass center. The default value is the child's mass
+        center.
+    parent_interframe : ReferenceFrame, optional
+        Intermediate frame of the parent body with respect to which the joint
+        transformation is formulated. If a Vector is provided then an interframe
+        is created which aligns its X axis with the given vector. The default
+        value is the parent's own frame.
+    child_interframe : ReferenceFrame, optional
+        Intermediate frame of the child body with respect to which the joint
+        transformation is formulated. If a Vector is provided then an interframe
+        is created which aligns its X axis with the given vector. The default
+        value is the child's own frame.
+    rot_type : str, optional
+        The method used to generate the direction cosine matrix. Supported
+        methods are:
+
+        - ``'Body'``: three successive rotations about new intermediate axes,
+          also called "Euler and Tait-Bryan angles"
+        - ``'Space'``: three successive rotations about the parent frames' unit
+          vectors
+
+        The default method is ``'Body'``.
+    amounts :
+        Expressions defining the rotation angles or direction cosine matrix.
+        These must match the ``rot_type``. See examples below for details. The
+        input types are:
+
+        - ``'Body'``: 3-tuple of expressions, symbols, or functions
+        - ``'Space'``: 3-tuple of expressions, symbols, or functions
+
+        The default amounts are the given ``coordinates``.
+    rot_order : str or int, optional
+        If applicable, the order of the successive of rotations. The string
+        ``'123'`` and integer ``123`` are equivalent, for example. Required for
+        ``'Body'`` and ``'Space'``. The default value is ``123``.
+
+    Attributes
+    ==========
+
+    name : string
+        The joint's name.
+    parent : Body
+        The joint's parent body.
+    child : Body
+        The joint's child body.
+    coordinates : Matrix
+        Matrix of the joint's generalized coordinates.
+    speeds : Matrix
+        Matrix of the joint's generalized speeds.
+    parent_point : Point
+        Attachment point where the joint is fixed to the parent body.
+    child_point : Point
+        Attachment point where the joint is fixed to the child body.
+    parent_interframe : ReferenceFrame
+        Intermediate frame of the parent body with respect to which the joint
+        transformation is formulated.
+    child_interframe : ReferenceFrame
+        Intermediate frame of the child body with respect to which the joint
+        transformation is formulated.
+    kdes : Matrix
+        Kinematical differential equations of the joint.
+
+    Examples
+    =========
+
+    A single spherical joint is created from two bodies and has the following
+    basic attributes:
+
+    >>> from sympy.physics.mechanics import Body, SphericalJoint
+    >>> parent = Body('P')
+    >>> parent
+    P
+    >>> child = Body('C')
+    >>> child
+    C
+    >>> joint = SphericalJoint('PC', parent, child)
+    >>> joint
+    SphericalJoint: PC  parent: P  child: C
+    >>> joint.name
+    'PC'
+    >>> joint.parent
+    P
+    >>> joint.child
+    C
+    >>> joint.parent_point
+    P_masscenter
+    >>> joint.child_point
+    C_masscenter
+    >>> joint.parent_interframe
+    P_frame
+    >>> joint.child_interframe
+    C_frame
+    >>> joint.coordinates
+    Matrix([
+    [q0_PC(t)],
+    [q1_PC(t)],
+    [q2_PC(t)]])
+    >>> joint.speeds
+    Matrix([
+    [u0_PC(t)],
+    [u1_PC(t)],
+    [u2_PC(t)]])
+    >>> child.frame.ang_vel_in(parent.frame).to_matrix(child.frame)
+    Matrix([
+    [ u0_PC(t)*cos(q1_PC(t))*cos(q2_PC(t)) + u1_PC(t)*sin(q2_PC(t))],
+    [-u0_PC(t)*sin(q2_PC(t))*cos(q1_PC(t)) + u1_PC(t)*cos(q2_PC(t))],
+    [                             u0_PC(t)*sin(q1_PC(t)) + u2_PC(t)]])
+    >>> child.frame.x.to_matrix(parent.frame)
+    Matrix([
+    [                                            cos(q1_PC(t))*cos(q2_PC(t))],
+    [sin(q0_PC(t))*sin(q1_PC(t))*cos(q2_PC(t)) + sin(q2_PC(t))*cos(q0_PC(t))],
+    [sin(q0_PC(t))*sin(q2_PC(t)) - sin(q1_PC(t))*cos(q0_PC(t))*cos(q2_PC(t))]])
+    >>> joint.child_point.pos_from(joint.parent_point)
+    0
+
+    To further demonstrate the use of the spherical joint, the kinematics of a
+    spherical joint with a ZXZ rotation can be created as follows.
+
+    >>> from sympy import symbols
+    >>> from sympy.physics.mechanics import Body, SphericalJoint
+    >>> l1 = symbols('l1')
+
+    First create bodies to represent the fixed floor and a pendulum bob.
+
+    >>> floor = Body('F')
+    >>> bob = Body('B')
+
+    The joint will connect the bob to the floor, with the joint located at a
+    distance of ``l1`` from the child's center of mass and the rotation set to a
+    body-fixed ZXZ rotation.
+
+    >>> joint = SphericalJoint('S', floor, bob, child_point=l1 * bob.y,
+    ...                        rot_type='body', rot_order='ZXZ')
+
+    Now that the joint is established, the kinematics of the connected body can
+    be accessed.
+
+    The position of the bob's masscenter is found with:
+
+    >>> bob.masscenter.pos_from(floor.masscenter)
+    - l1*B_frame.y
+
+    The angular velocities of the pendulum link can be computed with respect to
+    the floor.
+
+    >>> bob.frame.ang_vel_in(floor.frame).to_matrix(
+    ...     floor.frame).simplify()
+    Matrix([
+    [u1_S(t)*cos(q0_S(t)) + u2_S(t)*sin(q0_S(t))*sin(q1_S(t))],
+    [u1_S(t)*sin(q0_S(t)) - u2_S(t)*sin(q1_S(t))*cos(q0_S(t))],
+    [                          u0_S(t) + u2_S(t)*cos(q1_S(t))]])
+
+    Finally, the linear velocity of the bob's center of mass can be computed.
+
+    >>> bob.masscenter.vel(floor.frame).to_matrix(bob.frame)
+    Matrix([
+    [                           l1*(u0_S(t)*cos(q1_S(t)) + u2_S(t))],
+    [                                                             0],
+    [-l1*(u0_S(t)*sin(q1_S(t))*sin(q2_S(t)) + u1_S(t)*cos(q2_S(t)))]])
+
+    """
+    def __init__(self, name, parent, child, coordinates=None, speeds=None,
+                 parent_point=None, child_point=None, parent_interframe=None,
+                 child_interframe=None, rot_type='BODY', amounts=None,
+                 rot_order=123):
+        self._rot_type = rot_type
+        self._amounts = amounts
+        self._rot_order = rot_order
+        super().__init__(name, parent, child, coordinates, speeds,
+                         parent_point, child_point,
+                         parent_interframe=parent_interframe,
+                         child_interframe=child_interframe)
+
+    def __str__(self):
+        return (f'SphericalJoint: {self.name}  parent: {self.parent}  '
+                f'child: {self.child}')
+
+    def _generate_coordinates(self, coordinates):
+        return self._fill_coordinate_list(coordinates, 3, 'q')
+
+    def _generate_speeds(self, speeds):
+        return self._fill_coordinate_list(speeds, len(self.coordinates), 'u')
+
+    def _orient_frames(self):
+        supported_rot_types = ('BODY', 'SPACE')
+        if self._rot_type.upper() not in supported_rot_types:
+            raise NotImplementedError(
+                f'Rotation type "{self._rot_type}" is not implemented. '
+                f'Implemented rotation types are: {supported_rot_types}')
+        amounts = self.coordinates if self._amounts is None else self._amounts
+        self.child_interframe.orient(self.parent_interframe, self._rot_type,
+                                     amounts, self._rot_order)
+
+    def _set_angular_velocity(self):
+        t = dynamicsymbols._t
+        vel = self.child_interframe.ang_vel_in(self.parent_interframe).xreplace(
+            {q.diff(t): u for q, u in zip(self.coordinates, self.speeds)}
+        )
+        self.child_interframe.set_ang_vel(self.parent_interframe, vel)
+
+    def _set_linear_velocity(self):
+        self.child_point.set_pos(self.parent_point, 0)
+        self.parent_point.set_vel(self.parent.frame, 0)
+        self.child_point.set_vel(self.child.frame, 0)
+        self.child.masscenter.v2pt_theory(self.parent_point, self.parent.frame,
+                                          self.child.frame)
+
+
+class WeldJoint(Joint):
+    """Weld Joint.
+
+    .. image:: WeldJoint.svg
+        :align: center
+        :width: 500
+
+    Explanation
+    ===========
+
+    A weld joint is defined such that there is no relative motion between the
+    child and parent bodies. The direction cosine matrix between the attachment
+    frame (``parent_interframe`` and ``child_interframe``) is the identity
+    matrix and the attachment points (``parent_point`` and ``child_point``) are
+    coincident. The page on the joints framework gives a more detailed
+    explanation of the intermediate frames.
+
+    Parameters
+    ==========
+
+    name : string
+        A unique name for the joint.
+    parent : Body
+        The parent body of joint.
+    child : Body
+        The child body of joint.
+    parent_point : Point or Vector, optional
+        Attachment point where the joint is fixed to the parent body. If a
+        vector is provided, then the attachment point is computed by adding the
+        vector to the body's mass center. The default value is the parent's mass
+        center.
+    child_point : Point or Vector, optional
+        Attachment point where the joint is fixed to the child body. If a
+        vector is provided, then the attachment point is computed by adding the
+        vector to the body's mass center. The default value is the child's mass
+        center.
+    parent_interframe : ReferenceFrame, optional
+        Intermediate frame of the parent body with respect to which the joint
+        transformation is formulated. If a Vector is provided then an interframe
+        is created which aligns its X axis with the given vector. The default
+        value is the parent's own frame.
+    child_interframe : ReferenceFrame, optional
+        Intermediate frame of the child body with respect to which the joint
+        transformation is formulated. If a Vector is provided then an interframe
+        is created which aligns its X axis with the given vector. The default
+        value is the child's own frame.
+
+    Attributes
+    ==========
+
+    name : string
+        The joint's name.
+    parent : Body
+        The joint's parent body.
+    child : Body
+        The joint's child body.
+    coordinates : Matrix
+        Matrix of the joint's generalized coordinates. The default value is
+        ``dynamicsymbols(f'q_{joint.name}')``.
+    speeds : Matrix
+        Matrix of the joint's generalized speeds. The default value is
+        ``dynamicsymbols(f'u_{joint.name}')``.
+    parent_point : Point
+        Attachment point where the joint is fixed to the parent body.
+    child_point : Point
+        Attachment point where the joint is fixed to the child body.
+    parent_interframe : ReferenceFrame
+        Intermediate frame of the parent body with respect to which the joint
+        transformation is formulated.
+    child_interframe : ReferenceFrame
+        Intermediate frame of the child body with respect to which the joint
+        transformation is formulated.
+    kdes : Matrix
+        Kinematical differential equations of the joint.
+
+    Examples
+    =========
+
+    A single weld joint is created from two bodies and has the following basic
+    attributes:
+
+    >>> from sympy.physics.mechanics import Body, WeldJoint
+    >>> parent = Body('P')
+    >>> parent
+    P
+    >>> child = Body('C')
+    >>> child
+    C
+    >>> joint = WeldJoint('PC', parent, child)
+    >>> joint
+    WeldJoint: PC  parent: P  child: C
+    >>> joint.name
+    'PC'
+    >>> joint.parent
+    P
+    >>> joint.child
+    C
+    >>> joint.parent_point
+    P_masscenter
+    >>> joint.child_point
+    C_masscenter
+    >>> joint.coordinates
+    Matrix(0, 0, [])
+    >>> joint.speeds
+    Matrix(0, 0, [])
+    >>> joint.child.frame.ang_vel_in(joint.parent.frame)
+    0
+    >>> joint.child.frame.dcm(joint.parent.frame)
+    Matrix([
+    [1, 0, 0],
+    [0, 1, 0],
+    [0, 0, 1]])
+    >>> joint.child_point.pos_from(joint.parent_point)
+    0
+
+    To further demonstrate the use of the weld joint, two relatively-fixed
+    bodies rotated by a quarter turn about the Y axis can be created as follows:
+
+    >>> from sympy import symbols, pi
+    >>> from sympy.physics.mechanics import ReferenceFrame, Body, WeldJoint
+    >>> l1, l2 = symbols('l1 l2')
+
+    First create the bodies to represent the parent and rotated child body.
+
+    >>> parent = Body('P')
+    >>> child = Body('C')
+
+    Next the intermediate frame specifying the fixed rotation with respect to
+    the parent can be created.
+
+    >>> rotated_frame = ReferenceFrame('Pr')
+    >>> rotated_frame.orient_axis(parent.frame, parent.y, pi / 2)
+
+    The weld between the parent body and child body is located at a distance
+    ``l1`` from the parent's center of mass in the X direction and ``l2`` from
+    the child's center of mass in the child's negative X direction.
+
+    >>> weld = WeldJoint('weld', parent, child, parent_point=l1 * parent.x,
+    ...                  child_point=-l2 * child.x,
+    ...                  parent_interframe=rotated_frame)
+
+    Now that the joint has been established, the kinematics of the bodies can be
+    accessed. The direction cosine matrix of the child body with respect to the
+    parent can be found:
+
+    >>> child.dcm(parent)
+    Matrix([
+    [0, 0, -1],
+    [0, 1,  0],
+    [1, 0,  0]])
+
+    As can also been seen from the direction cosine matrix, the parent X axis is
+    aligned with the child's Z axis:
+    >>> parent.x == child.z
+    True
+
+    The position of the child's center of mass with respect to the parent's
+    center of mass can be found with:
+
+    >>> child.masscenter.pos_from(parent.masscenter)
+    l1*P_frame.x + l2*C_frame.x
+
+    The angular velocity of the child with respect to the parent is 0 as one
+    would expect.
+
+    >>> child.ang_vel_in(parent)
+    0
+
+    """
+
+    def __init__(self, name, parent, child, parent_point=None, child_point=None,
+                 parent_interframe=None, child_interframe=None):
+        super().__init__(name, parent, child, [], [], parent_point,
+                         child_point, parent_interframe=parent_interframe,
+                         child_interframe=child_interframe)
+        self._kdes = Matrix(1, 0, []).T  # Removes stackability problems #10770
+
+    def __str__(self):
+        return (f'WeldJoint: {self.name}  parent: {self.parent}  '
+                f'child: {self.child}')
+
+    def _generate_coordinates(self, coordinate):
+        return Matrix()
+
+    def _generate_speeds(self, speed):
+        return Matrix()
+
+    def _orient_frames(self):
+        self.child_interframe.orient_axis(self.parent_interframe,
+                                          self.parent_interframe.x, 0)
+
+    def _set_angular_velocity(self):
+        self.child_interframe.set_ang_vel(self.parent_interframe, 0)
+
+    def _set_linear_velocity(self):
+        self.child_point.set_pos(self.parent_point, 0)
+        self.parent_point.set_vel(self.parent.frame, 0)
+        self.child_point.set_vel(self.child.frame, 0)
+        self.child.masscenter.set_vel(self.parent.frame, 0)

venv/lib/python3.10/site-packages/sympy/physics/mechanics/jointsmethod.py

@@ -0,0 +1,279 @@
+from sympy.physics.mechanics import (Body, Lagrangian, KanesMethod, LagrangesMethod,
+                                    RigidBody, Particle)
+from sympy.physics.mechanics.method import _Methods
+from sympy.core.backend import Matrix
+
+__all__ = ['JointsMethod']
+
+
+class JointsMethod(_Methods):
+    """Method for formulating the equations of motion using a set of interconnected bodies with joints.
+
+    Parameters
+    ==========
+
+    newtonion : Body or ReferenceFrame
+        The newtonion(inertial) frame.
+    *joints : Joint
+        The joints in the system
+
+    Attributes
+    ==========
+
+    q, u : iterable
+        Iterable of the generalized coordinates and speeds
+    bodies : iterable
+        Iterable of Body objects in the system.
+    loads : iterable
+        Iterable of (Point, vector) or (ReferenceFrame, vector) tuples
+        describing the forces on the system.
+    mass_matrix : Matrix, shape(n, n)
+        The system's mass matrix
+    forcing : Matrix, shape(n, 1)
+        The system's forcing vector
+    mass_matrix_full : Matrix, shape(2*n, 2*n)
+        The "mass matrix" for the u's and q's
+    forcing_full : Matrix, shape(2*n, 1)
+        The "forcing vector" for the u's and q's
+    method : KanesMethod or Lagrange's method
+        Method's object.
+    kdes : iterable
+        Iterable of kde in they system.
+
+    Examples
+    ========
+
+    This is a simple example for a one degree of freedom translational
+    spring-mass-damper.
+
+    >>> from sympy import symbols
+    >>> from sympy.physics.mechanics import Body, JointsMethod, PrismaticJoint
+    >>> from sympy.physics.vector import dynamicsymbols
+    >>> c, k = symbols('c k')
+    >>> x, v = dynamicsymbols('x v')
+    >>> wall = Body('W')
+    >>> body = Body('B')
+    >>> J = PrismaticJoint('J', wall, body, coordinates=x, speeds=v)
+    >>> wall.apply_force(c*v*wall.x, reaction_body=body)
+    >>> wall.apply_force(k*x*wall.x, reaction_body=body)
+    >>> method = JointsMethod(wall, J)
+    >>> method.form_eoms()
+    Matrix([[-B_mass*Derivative(v(t), t) - c*v(t) - k*x(t)]])
+    >>> M = method.mass_matrix_full
+    >>> F = method.forcing_full
+    >>> rhs = M.LUsolve(F)
+    >>> rhs
+    Matrix([
+    [                     v(t)],
+    [(-c*v(t) - k*x(t))/B_mass]])
+
+    Notes
+    =====
+
+    ``JointsMethod`` currently only works with systems that do not have any
+    configuration or motion constraints.
+
+    """
+
+    def __init__(self, newtonion, *joints):
+        if isinstance(newtonion, Body):
+            self.frame = newtonion.frame
+        else:
+            self.frame = newtonion
+
+        self._joints = joints
+        self._bodies = self._generate_bodylist()
+        self._loads = self._generate_loadlist()
+        self._q = self._generate_q()
+        self._u = self._generate_u()
+        self._kdes = self._generate_kdes()
+
+        self._method = None
+
+    @property
+    def bodies(self):
+        """List of bodies in they system."""
+        return self._bodies
+
+    @property
+    def loads(self):
+        """List of loads on the system."""
+        return self._loads
+
+    @property
+    def q(self):
+        """List of the generalized coordinates."""
+        return self._q
+
+    @property
+    def u(self):
+        """List of the generalized speeds."""
+        return self._u
+
+    @property
+    def kdes(self):
+        """List of the generalized coordinates."""
+        return self._kdes
+
+    @property
+    def forcing_full(self):
+        """The "forcing vector" for the u's and q's."""
+        return self.method.forcing_full
+
+    @property
+    def mass_matrix_full(self):
+        """The "mass matrix" for the u's and q's."""
+        return self.method.mass_matrix_full
+
+    @property
+    def mass_matrix(self):
+        """The system's mass matrix."""
+        return self.method.mass_matrix
+
+    @property
+    def forcing(self):
+        """The system's forcing vector."""
+        return self.method.forcing
+
+    @property
+    def method(self):
+        """Object of method used to form equations of systems."""
+        return self._method
+
+    def _generate_bodylist(self):
+        bodies = []
+        for joint in self._joints:
+            if joint.child not in bodies:
+                bodies.append(joint.child)
+            if joint.parent not in bodies:
+                bodies.append(joint.parent)
+        return bodies
+
+    def _generate_loadlist(self):
+        load_list = []
+        for body in self.bodies:
+            load_list.extend(body.loads)
+        return load_list
+
+    def _generate_q(self):
+        q_ind = []
+        for joint in self._joints:
+            for coordinate in joint.coordinates:
+                if coordinate in q_ind:
+                    raise ValueError('Coordinates of joints should be unique.')
+                q_ind.append(coordinate)
+        return Matrix(q_ind)
+
+    def _generate_u(self):
+        u_ind = []
+        for joint in self._joints:
+            for speed in joint.speeds:
+                if speed in u_ind:
+                    raise ValueError('Speeds of joints should be unique.')
+                u_ind.append(speed)
+        return Matrix(u_ind)
+
+    def _generate_kdes(self):
+        kd_ind = Matrix(1, 0, []).T
+        for joint in self._joints:
+            kd_ind = kd_ind.col_join(joint.kdes)
+        return kd_ind
+
+    def _convert_bodies(self):
+        # Convert `Body` to `Particle` and `RigidBody`
+        bodylist = []
+        for body in self.bodies:
+            if body.is_rigidbody:
+                rb = RigidBody(body.name, body.masscenter, body.frame, body.mass,
+                    (body.central_inertia, body.masscenter))
+                rb.potential_energy = body.potential_energy
+                bodylist.append(rb)
+            else:
+                part = Particle(body.name, body.masscenter, body.mass)
+                part.potential_energy = body.potential_energy
+                bodylist.append(part)
+        return bodylist
+
+    def form_eoms(self, method=KanesMethod):
+        """Method to form system's equation of motions.
+
+        Parameters
+        ==========
+
+        method : Class
+            Class name of method.
+
+        Returns
+        ========
+
+        Matrix
+            Vector of equations of motions.
+
+        Examples
+        ========
+
+        This is a simple example for a one degree of freedom translational
+        spring-mass-damper.
+
+        >>> from sympy import S, symbols
+        >>> from sympy.physics.mechanics import LagrangesMethod, dynamicsymbols, Body
+        >>> from sympy.physics.mechanics import PrismaticJoint, JointsMethod
+        >>> q = dynamicsymbols('q')
+        >>> qd = dynamicsymbols('q', 1)
+        >>> m, k, b = symbols('m k b')
+        >>> wall = Body('W')
+        >>> part = Body('P', mass=m)
+        >>> part.potential_energy = k * q**2 / S(2)
+        >>> J = PrismaticJoint('J', wall, part, coordinates=q, speeds=qd)
+        >>> wall.apply_force(b * qd * wall.x, reaction_body=part)
+        >>> method = JointsMethod(wall, J)
+        >>> method.form_eoms(LagrangesMethod)
+        Matrix([[b*Derivative(q(t), t) + k*q(t) + m*Derivative(q(t), (t, 2))]])
+
+        We can also solve for the states using the 'rhs' method.
+
+        >>> method.rhs()
+        Matrix([
+        [                Derivative(q(t), t)],
+        [(-b*Derivative(q(t), t) - k*q(t))/m]])
+
+        """
+
+        bodylist = self._convert_bodies()
+        if issubclass(method, LagrangesMethod): #LagrangesMethod or similar
+            L = Lagrangian(self.frame, *bodylist)
+            self._method = method(L, self.q, self.loads, bodylist, self.frame)
+        else: #KanesMethod or similar
+            self._method = method(self.frame, q_ind=self.q, u_ind=self.u, kd_eqs=self.kdes,
+                                    forcelist=self.loads, bodies=bodylist)
+        soln = self.method._form_eoms()
+        return soln
+
+    def rhs(self, inv_method=None):
+        """Returns equations that can be solved numerically.
+
+        Parameters
+        ==========
+
+        inv_method : str
+            The specific sympy inverse matrix calculation method to use. For a
+            list of valid methods, see
+            :meth:`~sympy.matrices.matrices.MatrixBase.inv`
+
+        Returns
+        ========
+
+        Matrix
+            Numerically solvable equations.
+
+        See Also
+        ========
+
+        sympy.physics.mechanics.kane.KanesMethod.rhs:
+            KanesMethod's rhs function.
+        sympy.physics.mechanics.lagrange.LagrangesMethod.rhs:
+            LagrangesMethod's rhs function.
+
+        """
+
+        return self.method.rhs(inv_method=inv_method)

venv/lib/python3.10/site-packages/sympy/physics/mechanics/kane.py

@@ -0,0 +1,741 @@
+from sympy.core.backend import zeros, Matrix, diff, eye
+from sympy.core.sorting import default_sort_key
+from sympy.physics.vector import (ReferenceFrame, dynamicsymbols,
+                                  partial_velocity)
+from sympy.physics.mechanics.method import _Methods
+from sympy.physics.mechanics.particle import Particle
+from sympy.physics.mechanics.rigidbody import RigidBody
+from sympy.physics.mechanics.functions import (
+    msubs, find_dynamicsymbols, _f_list_parser, _validate_coordinates)
+from sympy.physics.mechanics.linearize import Linearizer
+from sympy.utilities.iterables import iterable
+
+__all__ = ['KanesMethod']
+
+
+class KanesMethod(_Methods):
+    r"""Kane's method object.
+
+    Explanation
+    ===========
+
+    This object is used to do the "book-keeping" as you go through and form
+    equations of motion in the way Kane presents in:
+    Kane, T., Levinson, D. Dynamics Theory and Applications. 1985 McGraw-Hill
+
+    The attributes are for equations in the form [M] udot = forcing.
+
+    Attributes
+    ==========
+
+    q, u : Matrix
+        Matrices of the generalized coordinates and speeds
+    bodies : iterable
+        Iterable of Point and RigidBody objects in the system.
+    loads : iterable
+        Iterable of (Point, vector) or (ReferenceFrame, vector) tuples
+        describing the forces on the system.
+    auxiliary_eqs : Matrix
+        If applicable, the set of auxiliary Kane's
+        equations used to solve for non-contributing
+        forces.
+    mass_matrix : Matrix
+        The system's dynamics mass matrix: [k_d; k_dnh]
+    forcing : Matrix
+        The system's dynamics forcing vector: -[f_d; f_dnh]
+    mass_matrix_kin : Matrix
+        The "mass matrix" for kinematic differential equations: k_kqdot
+    forcing_kin : Matrix
+        The forcing vector for kinematic differential equations: -(k_ku*u + f_k)
+    mass_matrix_full : Matrix
+        The "mass matrix" for the u's and q's with dynamics and kinematics
+    forcing_full : Matrix
+        The "forcing vector" for the u's and q's with dynamics and kinematics
+    explicit_kinematics : bool
+        Boolean whether the mass matrices and forcing vectors should use the
+        explicit form (default) or implicit form for kinematics.
+        See the notes for more details.
+
+    Notes
+    =====
+
+    The mass matrices and forcing vectors related to kinematic equations
+    are given in the explicit form by default. In other words, the kinematic
+    mass matrix is $\mathbf{k_{k\dot{q}}} = \mathbf{I}$.
+    In order to get the implicit form of those matrices/vectors, you can set the
+    ``explicit_kinematics`` attribute to ``False``. So $\mathbf{k_{k\dot{q}}}$ is not
+    necessarily an identity matrix. This can provide more compact equations for
+    non-simple kinematics (see #22626).
+
+    Examples
+    ========
+
+    This is a simple example for a one degree of freedom translational
+    spring-mass-damper.
+
+    In this example, we first need to do the kinematics.
+    This involves creating generalized speeds and coordinates and their
+    derivatives.
+    Then we create a point and set its velocity in a frame.
+
+        >>> from sympy import symbols
+        >>> from sympy.physics.mechanics import dynamicsymbols, ReferenceFrame
+        >>> from sympy.physics.mechanics import Point, Particle, KanesMethod
+        >>> q, u = dynamicsymbols('q u')
+        >>> qd, ud = dynamicsymbols('q u', 1)
+        >>> m, c, k = symbols('m c k')
+        >>> N = ReferenceFrame('N')
+        >>> P = Point('P')
+        >>> P.set_vel(N, u * N.x)
+
+    Next we need to arrange/store information in the way that KanesMethod
+    requires.  The kinematic differential equations need to be stored in a
+    dict.  A list of forces/torques must be constructed, where each entry in
+    the list is a (Point, Vector) or (ReferenceFrame, Vector) tuple, where the
+    Vectors represent the Force or Torque.
+    Next a particle needs to be created, and it needs to have a point and mass
+    assigned to it.
+    Finally, a list of all bodies and particles needs to be created.
+
+        >>> kd = [qd - u]
+        >>> FL = [(P, (-k * q - c * u) * N.x)]
+        >>> pa = Particle('pa', P, m)
+        >>> BL = [pa]
+
+    Finally we can generate the equations of motion.
+    First we create the KanesMethod object and supply an inertial frame,
+    coordinates, generalized speeds, and the kinematic differential equations.
+    Additional quantities such as configuration and motion constraints,
+    dependent coordinates and speeds, and auxiliary speeds are also supplied
+    here (see the online documentation).
+    Next we form FR* and FR to complete: Fr + Fr* = 0.
+    We have the equations of motion at this point.
+    It makes sense to rearrange them though, so we calculate the mass matrix and
+    the forcing terms, for E.o.M. in the form: [MM] udot = forcing, where MM is
+    the mass matrix, udot is a vector of the time derivatives of the
+    generalized speeds, and forcing is a vector representing "forcing" terms.
+
+        >>> KM = KanesMethod(N, q_ind=[q], u_ind=[u], kd_eqs=kd)
+        >>> (fr, frstar) = KM.kanes_equations(BL, FL)
+        >>> MM = KM.mass_matrix
+        >>> forcing = KM.forcing
+        >>> rhs = MM.inv() * forcing
+        >>> rhs
+        Matrix([[(-c*u(t) - k*q(t))/m]])
+        >>> KM.linearize(A_and_B=True)[0]
+        Matrix([
+        [   0,    1],
+        [-k/m, -c/m]])
+
+    Please look at the documentation pages for more information on how to
+    perform linearization and how to deal with dependent coordinates & speeds,
+    and how do deal with bringing non-contributing forces into evidence.
+
+    """
+
+    def __init__(self, frame, q_ind, u_ind, kd_eqs=None, q_dependent=None,
+            configuration_constraints=None, u_dependent=None,
+            velocity_constraints=None, acceleration_constraints=None,
+            u_auxiliary=None, bodies=None, forcelist=None, explicit_kinematics=True):
+
+        """Please read the online documentation. """
+        if not q_ind:
+            q_ind = [dynamicsymbols('dummy_q')]
+            kd_eqs = [dynamicsymbols('dummy_kd')]
+
+        if not isinstance(frame, ReferenceFrame):
+            raise TypeError('An inertial ReferenceFrame must be supplied')
+        self._inertial = frame
+
+        self._fr = None
+        self._frstar = None
+
+        self._forcelist = forcelist
+        self._bodylist = bodies
+
+        self.explicit_kinematics = explicit_kinematics
+
+        self._initialize_vectors(q_ind, q_dependent, u_ind, u_dependent,
+                u_auxiliary)
+        _validate_coordinates(self.q, self.u)
+        self._initialize_kindiffeq_matrices(kd_eqs)
+        self._initialize_constraint_matrices(configuration_constraints,
+                velocity_constraints, acceleration_constraints)
+
+    def _initialize_vectors(self, q_ind, q_dep, u_ind, u_dep, u_aux):
+        """Initialize the coordinate and speed vectors."""
+
+        none_handler = lambda x: Matrix(x) if x else Matrix()
+
+        # Initialize generalized coordinates
+        q_dep = none_handler(q_dep)
+        if not iterable(q_ind):
+            raise TypeError('Generalized coordinates must be an iterable.')
+        if not iterable(q_dep):
+            raise TypeError('Dependent coordinates must be an iterable.')
+        q_ind = Matrix(q_ind)
+        self._qdep = q_dep
+        self._q = Matrix([q_ind, q_dep])
+        self._qdot = self.q.diff(dynamicsymbols._t)
+
+        # Initialize generalized speeds
+        u_dep = none_handler(u_dep)
+        if not iterable(u_ind):
+            raise TypeError('Generalized speeds must be an iterable.')
+        if not iterable(u_dep):
+            raise TypeError('Dependent speeds must be an iterable.')
+        u_ind = Matrix(u_ind)
+        self._udep = u_dep
+        self._u = Matrix([u_ind, u_dep])
+        self._udot = self.u.diff(dynamicsymbols._t)
+        self._uaux = none_handler(u_aux)
+
+    def _initialize_constraint_matrices(self, config, vel, acc):
+        """Initializes constraint matrices."""
+
+        # Define vector dimensions
+        o = len(self.u)
+        m = len(self._udep)
+        p = o - m
+        none_handler = lambda x: Matrix(x) if x else Matrix()
+
+        # Initialize configuration constraints
+        config = none_handler(config)
+        if len(self._qdep) != len(config):
+            raise ValueError('There must be an equal number of dependent '
+                             'coordinates and configuration constraints.')
+        self._f_h = none_handler(config)
+
+        # Initialize velocity and acceleration constraints
+        vel = none_handler(vel)
+        acc = none_handler(acc)
+        if len(vel) != m:
+            raise ValueError('There must be an equal number of dependent '
+                             'speeds and velocity constraints.')
+        if acc and (len(acc) != m):
+            raise ValueError('There must be an equal number of dependent '
+                             'speeds and acceleration constraints.')
+        if vel:
+            u_zero = {i: 0 for i in self.u}
+            udot_zero = {i: 0 for i in self._udot}
+
+            # When calling kanes_equations, another class instance will be
+            # created if auxiliary u's are present. In this case, the
+            # computation of kinetic differential equation matrices will be
+            # skipped as this was computed during the original KanesMethod
+            # object, and the qd_u_map will not be available.
+            if self._qdot_u_map is not None:
+                vel = msubs(vel, self._qdot_u_map)
+
+            self._f_nh = msubs(vel, u_zero)
+            self._k_nh = (vel - self._f_nh).jacobian(self.u)
+            # If no acceleration constraints given, calculate them.
+            if not acc:
+                _f_dnh = (self._k_nh.diff(dynamicsymbols._t) * self.u +
+                          self._f_nh.diff(dynamicsymbols._t))
+                if self._qdot_u_map is not None:
+                    _f_dnh = msubs(_f_dnh, self._qdot_u_map)
+                self._f_dnh = _f_dnh
+                self._k_dnh = self._k_nh
+            else:
+                if self._qdot_u_map is not None:
+                    acc = msubs(acc, self._qdot_u_map)
+                self._f_dnh = msubs(acc, udot_zero)
+                self._k_dnh = (acc - self._f_dnh).jacobian(self._udot)
+
+            # Form of non-holonomic constraints is B*u + C = 0.
+            # We partition B into independent and dependent columns:
+            # Ars is then -B_dep.inv() * B_ind, and it relates dependent speeds
+            # to independent speeds as: udep = Ars*uind, neglecting the C term.
+            B_ind = self._k_nh[:, :p]
+            B_dep = self._k_nh[:, p:o]
+            self._Ars = -B_dep.LUsolve(B_ind)
+        else:
+            self._f_nh = Matrix()
+            self._k_nh = Matrix()
+            self._f_dnh = Matrix()
+            self._k_dnh = Matrix()
+            self._Ars = Matrix()
+
+    def _initialize_kindiffeq_matrices(self, kdeqs):
+        """Initialize the kinematic differential equation matrices.
+
+        Parameters
+        ==========
+        kdeqs : sequence of sympy expressions
+            Kinematic differential equations in the form of f(u,q',q,t) where
+            f() = 0. The equations have to be linear in the generalized
+            coordinates and generalized speeds.
+
+        """
+
+        if kdeqs:
+            if len(self.q) != len(kdeqs):
+                raise ValueError('There must be an equal number of kinematic '
+                                 'differential equations and coordinates.')
+
+            u = self.u
+            qdot = self._qdot
+
+            kdeqs = Matrix(kdeqs)
+
+            u_zero = {ui: 0 for ui in u}
+            uaux_zero = {uai: 0 for uai in self._uaux}
+            qdot_zero = {qdi: 0 for qdi in qdot}
+
+            # Extract the linear coefficient matrices as per the following
+            # equation:
+            #
+            # k_ku(q,t)*u(t) + k_kqdot(q,t)*q'(t) + f_k(q,t) = 0
+            #
+            k_ku = kdeqs.jacobian(u)
+            k_kqdot = kdeqs.jacobian(qdot)
+            f_k = kdeqs.xreplace(u_zero).xreplace(qdot_zero)
+
+            # The kinematic differential equations should be linear in both q'
+            # and u, so check for u and q' in the components.
+            dy_syms = find_dynamicsymbols(k_ku.row_join(k_kqdot).row_join(f_k))
+            nonlin_vars = [vari for vari in u[:] + qdot[:] if vari in dy_syms]
+            if nonlin_vars:
+                msg = ('The provided kinematic differential equations are '
+                       'nonlinear in {}. They must be linear in the '
+                       'generalized speeds and derivatives of the generalized '
+                       'coordinates.')
+                raise ValueError(msg.format(nonlin_vars))
+
+            self._f_k_implicit = f_k.xreplace(uaux_zero)
+            self._k_ku_implicit = k_ku.xreplace(uaux_zero)
+            self._k_kqdot_implicit = k_kqdot
+
+            # Solve for q'(t) such that the coefficient matrices are now in
+            # this form:
+            #
+            # k_kqdot^-1*k_ku*u(t) + I*q'(t) + k_kqdot^-1*f_k = 0
+            #
+            # NOTE : Solving the kinematic differential equations here is not
+            # necessary and prevents the equations from being provided in fully
+            # implicit form.
+            f_k_explicit = k_kqdot.LUsolve(f_k)
+            k_ku_explicit = k_kqdot.LUsolve(k_ku)
+            self._qdot_u_map = dict(zip(qdot, -(k_ku_explicit*u + f_k_explicit)))
+
+            self._f_k = f_k_explicit.xreplace(uaux_zero)
+            self._k_ku = k_ku_explicit.xreplace(uaux_zero)
+            self._k_kqdot = eye(len(qdot))
+
+        else:
+            self._qdot_u_map = None
+            self._f_k_implicit = self._f_k = Matrix()
+            self._k_ku_implicit = self._k_ku = Matrix()
+            self._k_kqdot_implicit = self._k_kqdot = Matrix()
+
+    def _form_fr(self, fl):
+        """Form the generalized active force."""
+        if fl is not None and (len(fl) == 0 or not iterable(fl)):
+            raise ValueError('Force pairs must be supplied in an '
+                'non-empty iterable or None.')
+
+        N = self._inertial
+        # pull out relevant velocities for constructing partial velocities
+        vel_list, f_list = _f_list_parser(fl, N)
+        vel_list = [msubs(i, self._qdot_u_map) for i in vel_list]
+        f_list = [msubs(i, self._qdot_u_map) for i in f_list]
+
+        # Fill Fr with dot product of partial velocities and forces
+        o = len(self.u)
+        b = len(f_list)
+        FR = zeros(o, 1)
+        partials = partial_velocity(vel_list, self.u, N)
+        for i in range(o):
+            FR[i] = sum(partials[j][i] & f_list[j] for j in range(b))
+
+        # In case there are dependent speeds
+        if self._udep:
+            p = o - len(self._udep)
+            FRtilde = FR[:p, 0]
+            FRold = FR[p:o, 0]
+            FRtilde += self._Ars.T * FRold
+            FR = FRtilde
+
+        self._forcelist = fl
+        self._fr = FR
+        return FR
+
+    def _form_frstar(self, bl):
+        """Form the generalized inertia force."""
+
+        if not iterable(bl):
+            raise TypeError('Bodies must be supplied in an iterable.')
+
+        t = dynamicsymbols._t
+        N = self._inertial
+        # Dicts setting things to zero
+        udot_zero = {i: 0 for i in self._udot}
+        uaux_zero = {i: 0 for i in self._uaux}
+        uauxdot = [diff(i, t) for i in self._uaux]
+        uauxdot_zero = {i: 0 for i in uauxdot}
+        # Dictionary of q' and q'' to u and u'
+        q_ddot_u_map = {k.diff(t): v.diff(t) for (k, v) in
+                self._qdot_u_map.items()}
+        q_ddot_u_map.update(self._qdot_u_map)
+
+        # Fill up the list of partials: format is a list with num elements
+        # equal to number of entries in body list. Each of these elements is a
+        # list - either of length 1 for the translational components of
+        # particles or of length 2 for the translational and rotational
+        # components of rigid bodies. The inner most list is the list of
+        # partial velocities.
+        def get_partial_velocity(body):
+            if isinstance(body, RigidBody):
+                vlist = [body.masscenter.vel(N), body.frame.ang_vel_in(N)]
+            elif isinstance(body, Particle):
+                vlist = [body.point.vel(N),]
+            else:
+                raise TypeError('The body list may only contain either '
+                                'RigidBody or Particle as list elements.')
+            v = [msubs(vel, self._qdot_u_map) for vel in vlist]
+            return partial_velocity(v, self.u, N)
+        partials = [get_partial_velocity(body) for body in bl]
+
+        # Compute fr_star in two components:
+        # fr_star = -(MM*u' + nonMM)
+        o = len(self.u)
+        MM = zeros(o, o)
+        nonMM = zeros(o, 1)
+        zero_uaux = lambda expr: msubs(expr, uaux_zero)
+        zero_udot_uaux = lambda expr: msubs(msubs(expr, udot_zero), uaux_zero)
+        for i, body in enumerate(bl):
+            if isinstance(body, RigidBody):
+                M = zero_uaux(body.mass)
+                I = zero_uaux(body.central_inertia)
+                vel = zero_uaux(body.masscenter.vel(N))
+                omega = zero_uaux(body.frame.ang_vel_in(N))
+                acc = zero_udot_uaux(body.masscenter.acc(N))
+                inertial_force = (M.diff(t) * vel + M * acc)
+                inertial_torque = zero_uaux((I.dt(body.frame) & omega) +
+                    msubs(I & body.frame.ang_acc_in(N), udot_zero) +
+                    (omega ^ (I & omega)))
+                for j in range(o):
+                    tmp_vel = zero_uaux(partials[i][0][j])
+                    tmp_ang = zero_uaux(I & partials[i][1][j])
+                    for k in range(o):
+                        # translational
+                        MM[j, k] += M * (tmp_vel & partials[i][0][k])
+                        # rotational
+                        MM[j, k] += (tmp_ang & partials[i][1][k])
+                    nonMM[j] += inertial_force & partials[i][0][j]
+                    nonMM[j] += inertial_torque & partials[i][1][j]
+            else:
+                M = zero_uaux(body.mass)
+                vel = zero_uaux(body.point.vel(N))
+                acc = zero_udot_uaux(body.point.acc(N))
+                inertial_force = (M.diff(t) * vel + M * acc)
+                for j in range(o):
+                    temp = zero_uaux(partials[i][0][j])
+                    for k in range(o):
+                        MM[j, k] += M * (temp & partials[i][0][k])
+                    nonMM[j] += inertial_force & partials[i][0][j]
+        # Compose fr_star out of MM and nonMM
+        MM = zero_uaux(msubs(MM, q_ddot_u_map))
+        nonMM = msubs(msubs(nonMM, q_ddot_u_map),
+                udot_zero, uauxdot_zero, uaux_zero)
+        fr_star = -(MM * msubs(Matrix(self._udot), uauxdot_zero) + nonMM)
+
+        # If there are dependent speeds, we need to find fr_star_tilde
+        if self._udep:
+            p = o - len(self._udep)
+            fr_star_ind = fr_star[:p, 0]
+            fr_star_dep = fr_star[p:o, 0]
+            fr_star = fr_star_ind + (self._Ars.T * fr_star_dep)
+            # Apply the same to MM
+            MMi = MM[:p, :]
+            MMd = MM[p:o, :]
+            MM = MMi + (self._Ars.T * MMd)
+
+        self._bodylist = bl
+        self._frstar = fr_star
+        self._k_d = MM
+        self._f_d = -msubs(self._fr + self._frstar, udot_zero)
+        return fr_star
+
+    def to_linearizer(self):
+        """Returns an instance of the Linearizer class, initiated from the
+        data in the KanesMethod class. This may be more desirable than using
+        the linearize class method, as the Linearizer object will allow more
+        efficient recalculation (i.e. about varying operating points)."""
+
+        if (self._fr is None) or (self._frstar is None):
+            raise ValueError('Need to compute Fr, Fr* first.')
+
+        # Get required equation components. The Kane's method class breaks
+        # these into pieces. Need to reassemble
+        f_c = self._f_h
+        if self._f_nh and self._k_nh:
+            f_v = self._f_nh + self._k_nh*Matrix(self.u)
+        else:
+            f_v = Matrix()
+        if self._f_dnh and self._k_dnh:
+            f_a = self._f_dnh + self._k_dnh*Matrix(self._udot)
+        else:
+            f_a = Matrix()
+        # Dicts to sub to zero, for splitting up expressions
+        u_zero = {i: 0 for i in self.u}
+        ud_zero = {i: 0 for i in self._udot}
+        qd_zero = {i: 0 for i in self._qdot}
+        qd_u_zero = {i: 0 for i in Matrix([self._qdot, self.u])}
+        # Break the kinematic differential eqs apart into f_0 and f_1
+        f_0 = msubs(self._f_k, u_zero) + self._k_kqdot*Matrix(self._qdot)
+        f_1 = msubs(self._f_k, qd_zero) + self._k_ku*Matrix(self.u)
+        # Break the dynamic differential eqs into f_2 and f_3
+        f_2 = msubs(self._frstar, qd_u_zero)
+        f_3 = msubs(self._frstar, ud_zero) + self._fr
+        f_4 = zeros(len(f_2), 1)
+
+        # Get the required vector components
+        q = self.q
+        u = self.u
+        if self._qdep:
+            q_i = q[:-len(self._qdep)]
+        else:
+            q_i = q
+        q_d = self._qdep
+        if self._udep:
+            u_i = u[:-len(self._udep)]
+        else:
+            u_i = u
+        u_d = self._udep
+
+        # Form dictionary to set auxiliary speeds & their derivatives to 0.
+        uaux = self._uaux
+        uauxdot = uaux.diff(dynamicsymbols._t)
+        uaux_zero = {i: 0 for i in Matrix([uaux, uauxdot])}
+
+        # Checking for dynamic symbols outside the dynamic differential
+        # equations; throws error if there is.
+        sym_list = set(Matrix([q, self._qdot, u, self._udot, uaux, uauxdot]))
+        if any(find_dynamicsymbols(i, sym_list) for i in [self._k_kqdot,
+                self._k_ku, self._f_k, self._k_dnh, self._f_dnh, self._k_d]):
+            raise ValueError('Cannot have dynamicsymbols outside dynamic \
+                             forcing vector.')
+
+        # Find all other dynamic symbols, forming the forcing vector r.
+        # Sort r to make it canonical.
+        r = list(find_dynamicsymbols(msubs(self._f_d, uaux_zero), sym_list))
+        r.sort(key=default_sort_key)
+
+        # Check for any derivatives of variables in r that are also found in r.
+        for i in r:
+            if diff(i, dynamicsymbols._t) in r:
+                raise ValueError('Cannot have derivatives of specified \
+                                 quantities when linearizing forcing terms.')
+        return Linearizer(f_0, f_1, f_2, f_3, f_4, f_c, f_v, f_a, q, u, q_i,
+                q_d, u_i, u_d, r)
+
+    # TODO : Remove `new_method` after 1.1 has been released.
+    def linearize(self, *, new_method=None, **kwargs):
+        """ Linearize the equations of motion about a symbolic operating point.
+
+        Explanation
+        ===========
+
+        If kwarg A_and_B is False (default), returns M, A, B, r for the
+        linearized form, M*[q', u']^T = A*[q_ind, u_ind]^T + B*r.
+
+        If kwarg A_and_B is True, returns A, B, r for the linearized form
+        dx = A*x + B*r, where x = [q_ind, u_ind]^T. Note that this is
+        computationally intensive if there are many symbolic parameters. For
+        this reason, it may be more desirable to use the default A_and_B=False,
+        returning M, A, and B. Values may then be substituted in to these
+        matrices, and the state space form found as
+        A = P.T*M.inv()*A, B = P.T*M.inv()*B, where P = Linearizer.perm_mat.
+
+        In both cases, r is found as all dynamicsymbols in the equations of
+        motion that are not part of q, u, q', or u'. They are sorted in
+        canonical form.
+
+        The operating points may be also entered using the ``op_point`` kwarg.
+        This takes a dictionary of {symbol: value}, or a an iterable of such
+        dictionaries. The values may be numeric or symbolic. The more values
+        you can specify beforehand, the faster this computation will run.
+
+        For more documentation, please see the ``Linearizer`` class."""
+        linearizer = self.to_linearizer()
+        result = linearizer.linearize(**kwargs)
+        return result + (linearizer.r,)
+
+    def kanes_equations(self, bodies=None, loads=None):
+        """ Method to form Kane's equations, Fr + Fr* = 0.
+
+        Explanation
+        ===========
+
+        Returns (Fr, Fr*). In the case where auxiliary generalized speeds are
+        present (say, s auxiliary speeds, o generalized speeds, and m motion
+        constraints) the length of the returned vectors will be o - m + s in
+        length. The first o - m equations will be the constrained Kane's
+        equations, then the s auxiliary Kane's equations. These auxiliary
+        equations can be accessed with the auxiliary_eqs property.
+
+        Parameters
+        ==========
+
+        bodies : iterable
+            An iterable of all RigidBody's and Particle's in the system.
+            A system must have at least one body.
+        loads : iterable
+            Takes in an iterable of (Particle, Vector) or (ReferenceFrame, Vector)
+            tuples which represent the force at a point or torque on a frame.
+            Must be either a non-empty iterable of tuples or None which corresponds
+            to a system with no constraints.
+        """
+        if bodies is None:
+            bodies = self.bodies
+        if  loads is None and self._forcelist is not None:
+            loads = self._forcelist
+        if loads == []:
+            loads = None
+        if not self._k_kqdot:
+            raise AttributeError('Create an instance of KanesMethod with '
+                    'kinematic differential equations to use this method.')
+        fr = self._form_fr(loads)
+        frstar = self._form_frstar(bodies)
+        if self._uaux:
+            if not self._udep:
+                km = KanesMethod(self._inertial, self.q, self._uaux,
+                             u_auxiliary=self._uaux)
+            else:
+                km = KanesMethod(self._inertial, self.q, self._uaux,
+                        u_auxiliary=self._uaux, u_dependent=self._udep,
+                        velocity_constraints=(self._k_nh * self.u +
+                        self._f_nh),
+                        acceleration_constraints=(self._k_dnh * self._udot +
+                        self._f_dnh)
+                        )
+            km._qdot_u_map = self._qdot_u_map
+            self._km = km
+            fraux = km._form_fr(loads)
+            frstaraux = km._form_frstar(bodies)
+            self._aux_eq = fraux + frstaraux
+            self._fr = fr.col_join(fraux)
+            self._frstar = frstar.col_join(frstaraux)
+        return (self._fr, self._frstar)
+
+    def _form_eoms(self):
+        fr, frstar = self.kanes_equations(self.bodylist, self.forcelist)
+        return fr + frstar
+
+    def rhs(self, inv_method=None):
+        """Returns the system's equations of motion in first order form. The
+        output is the right hand side of::
+
+           x' = |q'| =: f(q, u, r, p, t)
+                |u'|
+
+        The right hand side is what is needed by most numerical ODE
+        integrators.
+
+        Parameters
+        ==========
+
+        inv_method : str
+            The specific sympy inverse matrix calculation method to use. For a
+            list of valid methods, see
+            :meth:`~sympy.matrices.matrices.MatrixBase.inv`
+
+        """
+        rhs = zeros(len(self.q) + len(self.u), 1)
+        kdes = self.kindiffdict()
+        for i, q_i in enumerate(self.q):
+            rhs[i] = kdes[q_i.diff()]
+
+        if inv_method is None:
+            rhs[len(self.q):, 0] = self.mass_matrix.LUsolve(self.forcing)
+        else:
+            rhs[len(self.q):, 0] = (self.mass_matrix.inv(inv_method,
+                                                         try_block_diag=True) *
+                                    self.forcing)
+
+        return rhs
+
+    def kindiffdict(self):
+        """Returns a dictionary mapping q' to u."""
+        if not self._qdot_u_map:
+            raise AttributeError('Create an instance of KanesMethod with '
+                    'kinematic differential equations to use this method.')
+        return self._qdot_u_map
+
+    @property
+    def auxiliary_eqs(self):
+        """A matrix containing the auxiliary equations."""
+        if not self._fr or not self._frstar:
+            raise ValueError('Need to compute Fr, Fr* first.')
+        if not self._uaux:
+            raise ValueError('No auxiliary speeds have been declared.')
+        return self._aux_eq
+
+    @property
+    def mass_matrix_kin(self):
+        r"""The kinematic "mass matrix" $\mathbf{k_{k\dot{q}}}$ of the system."""
+        return self._k_kqdot if self.explicit_kinematics else self._k_kqdot_implicit
+
+    @property
+    def forcing_kin(self):
+        """The kinematic "forcing vector" of the system."""
+        if self.explicit_kinematics:
+            return -(self._k_ku * Matrix(self.u) + self._f_k)
+        else:
+            return -(self._k_ku_implicit * Matrix(self.u) + self._f_k_implicit)
+
+    @property
+    def mass_matrix(self):
+        """The mass matrix of the system."""
+        if not self._fr or not self._frstar:
+            raise ValueError('Need to compute Fr, Fr* first.')
+        return Matrix([self._k_d, self._k_dnh])
+
+    @property
+    def forcing(self):
+        """The forcing vector of the system."""
+        if not self._fr or not self._frstar:
+            raise ValueError('Need to compute Fr, Fr* first.')
+        return -Matrix([self._f_d, self._f_dnh])
+
+    @property
+    def mass_matrix_full(self):
+        """The mass matrix of the system, augmented by the kinematic
+        differential equations in explicit or implicit form."""
+        if not self._fr or not self._frstar:
+            raise ValueError('Need to compute Fr, Fr* first.')
+        o, n = len(self.u), len(self.q)
+        return (self.mass_matrix_kin.row_join(zeros(n, o))).col_join(
+            zeros(o, n).row_join(self.mass_matrix))
+
+    @property
+    def forcing_full(self):
+        """The forcing vector of the system, augmented by the kinematic
+        differential equations in explicit or implicit form."""
+        return Matrix([self.forcing_kin, self.forcing])
+
+    @property
+    def q(self):
+        return self._q
+
+    @property
+    def u(self):
+        return self._u
+
+    @property
+    def bodylist(self):
+        return self._bodylist
+
+    @property
+    def forcelist(self):
+        return self._forcelist
+
+    @property
+    def bodies(self):
+        return self._bodylist
+
+    @property
+    def loads(self):
+        return self._forcelist

venv/lib/python3.10/site-packages/sympy/physics/mechanics/lagrange.py

@@ -0,0 +1,477 @@
+from sympy.core.backend import diff, zeros, Matrix, eye, sympify
+from sympy.core.sorting import default_sort_key
+from sympy.physics.vector import dynamicsymbols, ReferenceFrame
+from sympy.physics.mechanics.method import _Methods
+from sympy.physics.mechanics.functions import (
+    find_dynamicsymbols, msubs, _f_list_parser, _validate_coordinates)
+from sympy.physics.mechanics.linearize import Linearizer
+from sympy.utilities.iterables import iterable
+
+__all__ = ['LagrangesMethod']
+
+
+class LagrangesMethod(_Methods):
+    """Lagrange's method object.
+
+    Explanation
+    ===========
+
+    This object generates the equations of motion in a two step procedure. The
+    first step involves the initialization of LagrangesMethod by supplying the
+    Lagrangian and the generalized coordinates, at the bare minimum. If there
+    are any constraint equations, they can be supplied as keyword arguments.
+    The Lagrange multipliers are automatically generated and are equal in
+    number to the constraint equations. Similarly any non-conservative forces
+    can be supplied in an iterable (as described below and also shown in the
+    example) along with a ReferenceFrame. This is also discussed further in the
+    __init__ method.
+
+    Attributes
+    ==========
+
+    q, u : Matrix
+        Matrices of the generalized coordinates and speeds
+    loads : iterable
+        Iterable of (Point, vector) or (ReferenceFrame, vector) tuples
+        describing the forces on the system.
+    bodies : iterable
+        Iterable containing the rigid bodies and particles of the system.
+    mass_matrix : Matrix
+        The system's mass matrix
+    forcing : Matrix
+        The system's forcing vector
+    mass_matrix_full : Matrix
+        The "mass matrix" for the qdot's, qdoubledot's, and the
+        lagrange multipliers (lam)
+    forcing_full : Matrix
+        The forcing vector for the qdot's, qdoubledot's and
+        lagrange multipliers (lam)
+
+    Examples
+    ========
+
+    This is a simple example for a one degree of freedom translational
+    spring-mass-damper.
+
+    In this example, we first need to do the kinematics.
+    This involves creating generalized coordinates and their derivatives.
+    Then we create a point and set its velocity in a frame.
+
+        >>> from sympy.physics.mechanics import LagrangesMethod, Lagrangian
+        >>> from sympy.physics.mechanics import ReferenceFrame, Particle, Point
+        >>> from sympy.physics.mechanics import dynamicsymbols
+        >>> from sympy import symbols
+        >>> q = dynamicsymbols('q')
+        >>> qd = dynamicsymbols('q', 1)
+        >>> m, k, b = symbols('m k b')
+        >>> N = ReferenceFrame('N')
+        >>> P = Point('P')
+        >>> P.set_vel(N, qd * N.x)
+
+    We need to then prepare the information as required by LagrangesMethod to
+    generate equations of motion.
+    First we create the Particle, which has a point attached to it.
+    Following this the lagrangian is created from the kinetic and potential
+    energies.
+    Then, an iterable of nonconservative forces/torques must be constructed,
+    where each item is a (Point, Vector) or (ReferenceFrame, Vector) tuple,
+    with the Vectors representing the nonconservative forces or torques.
+
+        >>> Pa = Particle('Pa', P, m)
+        >>> Pa.potential_energy = k * q**2 / 2.0
+        >>> L = Lagrangian(N, Pa)
+        >>> fl = [(P, -b * qd * N.x)]
+
+    Finally we can generate the equations of motion.
+    First we create the LagrangesMethod object. To do this one must supply
+    the Lagrangian, and the generalized coordinates. The constraint equations,
+    the forcelist, and the inertial frame may also be provided, if relevant.
+    Next we generate Lagrange's equations of motion, such that:
+    Lagrange's equations of motion = 0.
+    We have the equations of motion at this point.
+
+        >>> l = LagrangesMethod(L, [q], forcelist = fl, frame = N)
+        >>> print(l.form_lagranges_equations())
+        Matrix([[b*Derivative(q(t), t) + 1.0*k*q(t) + m*Derivative(q(t), (t, 2))]])
+
+    We can also solve for the states using the 'rhs' method.
+
+        >>> print(l.rhs())
+        Matrix([[Derivative(q(t), t)], [(-b*Derivative(q(t), t) - 1.0*k*q(t))/m]])
+
+    Please refer to the docstrings on each method for more details.
+    """
+
+    def __init__(self, Lagrangian, qs, forcelist=None, bodies=None, frame=None,
+                 hol_coneqs=None, nonhol_coneqs=None):
+        """Supply the following for the initialization of LagrangesMethod.
+
+        Lagrangian : Sympifyable
+
+        qs : array_like
+            The generalized coordinates
+
+        hol_coneqs : array_like, optional
+            The holonomic constraint equations
+
+        nonhol_coneqs : array_like, optional
+            The nonholonomic constraint equations
+
+        forcelist : iterable, optional
+            Takes an iterable of (Point, Vector) or (ReferenceFrame, Vector)
+            tuples which represent the force at a point or torque on a frame.
+            This feature is primarily to account for the nonconservative forces
+            and/or moments.
+
+        bodies : iterable, optional
+            Takes an iterable containing the rigid bodies and particles of the
+            system.
+
+        frame : ReferenceFrame, optional
+            Supply the inertial frame. This is used to determine the
+            generalized forces due to non-conservative forces.
+        """
+
+        self._L = Matrix([sympify(Lagrangian)])
+        self.eom = None
+        self._m_cd = Matrix()           # Mass Matrix of differentiated coneqs
+        self._m_d = Matrix()            # Mass Matrix of dynamic equations
+        self._f_cd = Matrix()           # Forcing part of the diff coneqs
+        self._f_d = Matrix()            # Forcing part of the dynamic equations
+        self.lam_coeffs = Matrix()      # The coeffecients of the multipliers
+
+        forcelist = forcelist if forcelist else []
+        if not iterable(forcelist):
+            raise TypeError('Force pairs must be supplied in an iterable.')
+        self._forcelist = forcelist
+        if frame and not isinstance(frame, ReferenceFrame):
+            raise TypeError('frame must be a valid ReferenceFrame')
+        self._bodies = bodies
+        self.inertial = frame
+
+        self.lam_vec = Matrix()
+
+        self._term1 = Matrix()
+        self._term2 = Matrix()
+        self._term3 = Matrix()
+        self._term4 = Matrix()
+
+        # Creating the qs, qdots and qdoubledots
+        if not iterable(qs):
+            raise TypeError('Generalized coordinates must be an iterable')
+        self._q = Matrix(qs)
+        self._qdots = self.q.diff(dynamicsymbols._t)
+        self._qdoubledots = self._qdots.diff(dynamicsymbols._t)
+        _validate_coordinates(self.q)
+
+        mat_build = lambda x: Matrix(x) if x else Matrix()
+        hol_coneqs = mat_build(hol_coneqs)
+        nonhol_coneqs = mat_build(nonhol_coneqs)
+        self.coneqs = Matrix([hol_coneqs.diff(dynamicsymbols._t),
+                nonhol_coneqs])
+        self._hol_coneqs = hol_coneqs
+
+    def form_lagranges_equations(self):
+        """Method to form Lagrange's equations of motion.
+
+        Returns a vector of equations of motion using Lagrange's equations of
+        the second kind.
+        """
+
+        qds = self._qdots
+        qdd_zero = {i: 0 for i in self._qdoubledots}
+        n = len(self.q)
+
+        # Internally we represent the EOM as four terms:
+        # EOM = term1 - term2 - term3 - term4 = 0
+
+        # First term
+        self._term1 = self._L.jacobian(qds)
+        self._term1 = self._term1.diff(dynamicsymbols._t).T
+
+        # Second term
+        self._term2 = self._L.jacobian(self.q).T
+
+        # Third term
+        if self.coneqs:
+            coneqs = self.coneqs
+            m = len(coneqs)
+            # Creating the multipliers
+            self.lam_vec = Matrix(dynamicsymbols('lam1:' + str(m + 1)))
+            self.lam_coeffs = -coneqs.jacobian(qds)
+            self._term3 = self.lam_coeffs.T * self.lam_vec
+            # Extracting the coeffecients of the qdds from the diff coneqs
+            diffconeqs = coneqs.diff(dynamicsymbols._t)
+            self._m_cd = diffconeqs.jacobian(self._qdoubledots)
+            # The remaining terms i.e. the 'forcing' terms in diff coneqs
+            self._f_cd = -diffconeqs.subs(qdd_zero)
+        else:
+            self._term3 = zeros(n, 1)
+
+        # Fourth term
+        if self.forcelist:
+            N = self.inertial
+            self._term4 = zeros(n, 1)
+            for i, qd in enumerate(qds):
+                flist = zip(*_f_list_parser(self.forcelist, N))
+                self._term4[i] = sum(v.diff(qd, N) & f for (v, f) in flist)
+        else:
+            self._term4 = zeros(n, 1)
+
+        # Form the dynamic mass and forcing matrices
+        without_lam = self._term1 - self._term2 - self._term4
+        self._m_d = without_lam.jacobian(self._qdoubledots)
+        self._f_d = -without_lam.subs(qdd_zero)
+
+        # Form the EOM
+        self.eom = without_lam - self._term3
+        return self.eom
+
+    def _form_eoms(self):
+        return self.form_lagranges_equations()
+
+    @property
+    def mass_matrix(self):
+        """Returns the mass matrix, which is augmented by the Lagrange
+        multipliers, if necessary.
+
+        Explanation
+        ===========
+
+        If the system is described by 'n' generalized coordinates and there are
+        no constraint equations then an n X n matrix is returned.
+
+        If there are 'n' generalized coordinates and 'm' constraint equations
+        have been supplied during initialization then an n X (n+m) matrix is
+        returned. The (n + m - 1)th and (n + m)th columns contain the
+        coefficients of the Lagrange multipliers.
+        """
+
+        if self.eom is None:
+            raise ValueError('Need to compute the equations of motion first')
+        if self.coneqs:
+            return (self._m_d).row_join(self.lam_coeffs.T)
+        else:
+            return self._m_d
+
+    @property
+    def mass_matrix_full(self):
+        """Augments the coefficients of qdots to the mass_matrix."""
+
+        if self.eom is None:
+            raise ValueError('Need to compute the equations of motion first')
+        n = len(self.q)
+        m = len(self.coneqs)
+        row1 = eye(n).row_join(zeros(n, n + m))
+        row2 = zeros(n, n).row_join(self.mass_matrix)
+        if self.coneqs:
+            row3 = zeros(m, n).row_join(self._m_cd).row_join(zeros(m, m))
+            return row1.col_join(row2).col_join(row3)
+        else:
+            return row1.col_join(row2)
+
+    @property
+    def forcing(self):
+        """Returns the forcing vector from 'lagranges_equations' method."""
+
+        if self.eom is None:
+            raise ValueError('Need to compute the equations of motion first')
+        return self._f_d
+
+    @property
+    def forcing_full(self):
+        """Augments qdots to the forcing vector above."""
+
+        if self.eom is None:
+            raise ValueError('Need to compute the equations of motion first')
+        if self.coneqs:
+            return self._qdots.col_join(self.forcing).col_join(self._f_cd)
+        else:
+            return self._qdots.col_join(self.forcing)
+
+    def to_linearizer(self, q_ind=None, qd_ind=None, q_dep=None, qd_dep=None):
+        """Returns an instance of the Linearizer class, initiated from the
+        data in the LagrangesMethod class. This may be more desirable than using
+        the linearize class method, as the Linearizer object will allow more
+        efficient recalculation (i.e. about varying operating points).
+
+        Parameters
+        ==========
+
+        q_ind, qd_ind : array_like, optional
+            The independent generalized coordinates and speeds.
+        q_dep, qd_dep : array_like, optional
+            The dependent generalized coordinates and speeds.
+        """
+
+        # Compose vectors
+        t = dynamicsymbols._t
+        q = self.q
+        u = self._qdots
+        ud = u.diff(t)
+        # Get vector of lagrange multipliers
+        lams = self.lam_vec
+
+        mat_build = lambda x: Matrix(x) if x else Matrix()
+        q_i = mat_build(q_ind)
+        q_d = mat_build(q_dep)
+        u_i = mat_build(qd_ind)
+        u_d = mat_build(qd_dep)
+
+        # Compose general form equations
+        f_c = self._hol_coneqs
+        f_v = self.coneqs
+        f_a = f_v.diff(t)
+        f_0 = u
+        f_1 = -u
+        f_2 = self._term1
+        f_3 = -(self._term2 + self._term4)
+        f_4 = -self._term3
+
+        # Check that there are an appropriate number of independent and
+        # dependent coordinates
+        if len(q_d) != len(f_c) or len(u_d) != len(f_v):
+            raise ValueError(("Must supply {:} dependent coordinates, and " +
+                    "{:} dependent speeds").format(len(f_c), len(f_v)))
+        if set(Matrix([q_i, q_d])) != set(q):
+            raise ValueError("Must partition q into q_ind and q_dep, with " +
+                    "no extra or missing symbols.")
+        if set(Matrix([u_i, u_d])) != set(u):
+            raise ValueError("Must partition qd into qd_ind and qd_dep, " +
+                    "with no extra or missing symbols.")
+
+        # Find all other dynamic symbols, forming the forcing vector r.
+        # Sort r to make it canonical.
+        insyms = set(Matrix([q, u, ud, lams]))
+        r = list(find_dynamicsymbols(f_3, insyms))
+        r.sort(key=default_sort_key)
+        # Check for any derivatives of variables in r that are also found in r.
+        for i in r:
+            if diff(i, dynamicsymbols._t) in r:
+                raise ValueError('Cannot have derivatives of specified \
+                                 quantities when linearizing forcing terms.')
+
+        return Linearizer(f_0, f_1, f_2, f_3, f_4, f_c, f_v, f_a, q, u, q_i,
+                q_d, u_i, u_d, r, lams)
+
+    def linearize(self, q_ind=None, qd_ind=None, q_dep=None, qd_dep=None,
+            **kwargs):
+        """Linearize the equations of motion about a symbolic operating point.
+
+        Explanation
+        ===========
+
+        If kwarg A_and_B is False (default), returns M, A, B, r for the
+        linearized form, M*[q', u']^T = A*[q_ind, u_ind]^T + B*r.
+
+        If kwarg A_and_B is True, returns A, B, r for the linearized form
+        dx = A*x + B*r, where x = [q_ind, u_ind]^T. Note that this is
+        computationally intensive if there are many symbolic parameters. For
+        this reason, it may be more desirable to use the default A_and_B=False,
+        returning M, A, and B. Values may then be substituted in to these
+        matrices, and the state space form found as
+        A = P.T*M.inv()*A, B = P.T*M.inv()*B, where P = Linearizer.perm_mat.
+
+        In both cases, r is found as all dynamicsymbols in the equations of
+        motion that are not part of q, u, q', or u'. They are sorted in
+        canonical form.
+
+        The operating points may be also entered using the ``op_point`` kwarg.
+        This takes a dictionary of {symbol: value}, or a an iterable of such
+        dictionaries. The values may be numeric or symbolic. The more values
+        you can specify beforehand, the faster this computation will run.
+
+        For more documentation, please see the ``Linearizer`` class."""
+
+        linearizer = self.to_linearizer(q_ind, qd_ind, q_dep, qd_dep)
+        result = linearizer.linearize(**kwargs)
+        return result + (linearizer.r,)
+
+    def solve_multipliers(self, op_point=None, sol_type='dict'):
+        """Solves for the values of the lagrange multipliers symbolically at
+        the specified operating point.
+
+        Parameters
+        ==========
+
+        op_point : dict or iterable of dicts, optional
+            Point at which to solve at. The operating point is specified as
+            a dictionary or iterable of dictionaries of {symbol: value}. The
+            value may be numeric or symbolic itself.
+
+        sol_type : str, optional
+            Solution return type. Valid options are:
+            - 'dict': A dict of {symbol : value} (default)
+            - 'Matrix': An ordered column matrix of the solution
+        """
+
+        # Determine number of multipliers
+        k = len(self.lam_vec)
+        if k == 0:
+            raise ValueError("System has no lagrange multipliers to solve for.")
+        # Compose dict of operating conditions
+        if isinstance(op_point, dict):
+            op_point_dict = op_point
+        elif iterable(op_point):
+            op_point_dict = {}
+            for op in op_point:
+                op_point_dict.update(op)
+        elif op_point is None:
+            op_point_dict = {}
+        else:
+            raise TypeError("op_point must be either a dictionary or an "
+                            "iterable of dictionaries.")
+        # Compose the system to be solved
+        mass_matrix = self.mass_matrix.col_join(-self.lam_coeffs.row_join(
+                zeros(k, k)))
+        force_matrix = self.forcing.col_join(self._f_cd)
+        # Sub in the operating point
+        mass_matrix = msubs(mass_matrix, op_point_dict)
+        force_matrix = msubs(force_matrix, op_point_dict)
+        # Solve for the multipliers
+        sol_list = mass_matrix.LUsolve(-force_matrix)[-k:]
+        if sol_type == 'dict':
+            return dict(zip(self.lam_vec, sol_list))
+        elif sol_type == 'Matrix':
+            return Matrix(sol_list)
+        else:
+            raise ValueError("Unknown sol_type {:}.".format(sol_type))
+
+    def rhs(self, inv_method=None, **kwargs):
+        """Returns equations that can be solved numerically.
+
+        Parameters
+        ==========
+
+        inv_method : str
+            The specific sympy inverse matrix calculation method to use. For a
+            list of valid methods, see
+            :meth:`~sympy.matrices.matrices.MatrixBase.inv`
+        """
+
+        if inv_method is None:
+            self._rhs = self.mass_matrix_full.LUsolve(self.forcing_full)
+        else:
+            self._rhs = (self.mass_matrix_full.inv(inv_method,
+                         try_block_diag=True) * self.forcing_full)
+        return self._rhs
+
+    @property
+    def q(self):
+        return self._q
+
+    @property
+    def u(self):
+        return self._qdots
+
+    @property
+    def bodies(self):
+        return self._bodies
+
+    @property
+    def forcelist(self):
+        return self._forcelist
+
+    @property
+    def loads(self):
+        return self._forcelist

venv/lib/python3.10/site-packages/sympy/physics/mechanics/linearize.py

@@ -0,0 +1,443 @@
+__all__ = ['Linearizer']
+
+from sympy.core.backend import Matrix, eye, zeros
+from sympy.core.symbol import Dummy
+from sympy.utilities.iterables import flatten
+from sympy.physics.vector import dynamicsymbols
+from sympy.physics.mechanics.functions import msubs
+
+from collections import namedtuple
+from collections.abc import Iterable
+
+class Linearizer:
+    """This object holds the general model form for a dynamic system.
+    This model is used for computing the linearized form of the system,
+    while properly dealing with constraints leading to  dependent
+    coordinates and speeds.
+
+    Attributes
+    ==========
+
+    f_0, f_1, f_2, f_3, f_4, f_c, f_v, f_a : Matrix
+        Matrices holding the general system form.
+    q, u, r : Matrix
+        Matrices holding the generalized coordinates, speeds, and
+        input vectors.
+    q_i, u_i : Matrix
+        Matrices of the independent generalized coordinates and speeds.
+    q_d, u_d : Matrix
+        Matrices of the dependent generalized coordinates and speeds.
+    perm_mat : Matrix
+        Permutation matrix such that [q_ind, u_ind]^T = perm_mat*[q, u]^T
+    """
+
+    def __init__(self, f_0, f_1, f_2, f_3, f_4, f_c, f_v, f_a, q, u,
+            q_i=None, q_d=None, u_i=None, u_d=None, r=None, lams=None):
+        """
+        Parameters
+        ==========
+
+        f_0, f_1, f_2, f_3, f_4, f_c, f_v, f_a : array_like
+            System of equations holding the general system form.
+            Supply empty array or Matrix if the parameter
+            does not exist.
+        q : array_like
+            The generalized coordinates.
+        u : array_like
+            The generalized speeds
+        q_i, u_i : array_like, optional
+            The independent generalized coordinates and speeds.
+        q_d, u_d : array_like, optional
+            The dependent generalized coordinates and speeds.
+        r : array_like, optional
+            The input variables.
+        lams : array_like, optional
+            The lagrange multipliers
+        """
+
+        # Generalized equation form
+        self.f_0 = Matrix(f_0)
+        self.f_1 = Matrix(f_1)
+        self.f_2 = Matrix(f_2)
+        self.f_3 = Matrix(f_3)
+        self.f_4 = Matrix(f_4)
+        self.f_c = Matrix(f_c)
+        self.f_v = Matrix(f_v)
+        self.f_a = Matrix(f_a)
+
+        # Generalized equation variables
+        self.q = Matrix(q)
+        self.u = Matrix(u)
+        none_handler = lambda x: Matrix(x) if x else Matrix()
+        self.q_i = none_handler(q_i)
+        self.q_d = none_handler(q_d)
+        self.u_i = none_handler(u_i)
+        self.u_d = none_handler(u_d)
+        self.r = none_handler(r)
+        self.lams = none_handler(lams)
+
+        # Derivatives of generalized equation variables
+        self._qd = self.q.diff(dynamicsymbols._t)
+        self._ud = self.u.diff(dynamicsymbols._t)
+        # If the user doesn't actually use generalized variables, and the
+        # qd and u vectors have any intersecting variables, this can cause
+        # problems. We'll fix this with some hackery, and Dummy variables
+        dup_vars = set(self._qd).intersection(self.u)
+        self._qd_dup = Matrix([var if var not in dup_vars else Dummy()
+            for var in self._qd])
+
+        # Derive dimesion terms
+        l = len(self.f_c)
+        m = len(self.f_v)
+        n = len(self.q)
+        o = len(self.u)
+        s = len(self.r)
+        k = len(self.lams)
+        dims = namedtuple('dims', ['l', 'm', 'n', 'o', 's', 'k'])
+        self._dims = dims(l, m, n, o, s, k)
+
+        self._Pq = None
+        self._Pqi = None
+        self._Pqd = None
+        self._Pu = None
+        self._Pui = None
+        self._Pud = None
+        self._C_0 = None
+        self._C_1 = None
+        self._C_2 = None
+        self.perm_mat = None
+
+        self._setup_done = False
+
+    def _setup(self):
+        # Calculations here only need to be run once. They are moved out of
+        # the __init__ method to increase the speed of Linearizer creation.
+        self._form_permutation_matrices()
+        self._form_block_matrices()
+        self._form_coefficient_matrices()
+        self._setup_done = True
+
+    def _form_permutation_matrices(self):
+        """Form the permutation matrices Pq and Pu."""
+
+        # Extract dimension variables
+        l, m, n, o, s, k = self._dims
+        # Compute permutation matrices
+        if n != 0:
+            self._Pq = permutation_matrix(self.q, Matrix([self.q_i, self.q_d]))
+            if l > 0:
+                self._Pqi = self._Pq[:, :-l]
+                self._Pqd = self._Pq[:, -l:]
+            else:
+                self._Pqi = self._Pq
+                self._Pqd = Matrix()
+        if o != 0:
+            self._Pu = permutation_matrix(self.u, Matrix([self.u_i, self.u_d]))
+            if m > 0:
+                self._Pui = self._Pu[:, :-m]
+                self._Pud = self._Pu[:, -m:]
+            else:
+                self._Pui = self._Pu
+                self._Pud = Matrix()
+        # Compute combination permutation matrix for computing A and B
+        P_col1 = Matrix([self._Pqi, zeros(o + k, n - l)])
+        P_col2 = Matrix([zeros(n, o - m), self._Pui, zeros(k, o - m)])
+        if P_col1:
+            if P_col2:
+                self.perm_mat = P_col1.row_join(P_col2)
+            else:
+                self.perm_mat = P_col1
+        else:
+            self.perm_mat = P_col2
+
+    def _form_coefficient_matrices(self):
+        """Form the coefficient matrices C_0, C_1, and C_2."""
+
+        # Extract dimension variables
+        l, m, n, o, s, k = self._dims
+        # Build up the coefficient matrices C_0, C_1, and C_2
+        # If there are configuration constraints (l > 0), form C_0 as normal.
+        # If not, C_0 is I_(nxn). Note that this works even if n=0
+        if l > 0:
+            f_c_jac_q = self.f_c.jacobian(self.q)
+            self._C_0 = (eye(n) - self._Pqd * (f_c_jac_q *
+                    self._Pqd).LUsolve(f_c_jac_q)) * self._Pqi
+        else:
+            self._C_0 = eye(n)
+        # If there are motion constraints (m > 0), form C_1 and C_2 as normal.
+        # If not, C_1 is 0, and C_2 is I_(oxo). Note that this works even if
+        # o = 0.
+        if m > 0:
+            f_v_jac_u = self.f_v.jacobian(self.u)
+            temp = f_v_jac_u * self._Pud
+            if n != 0:
+                f_v_jac_q = self.f_v.jacobian(self.q)
+                self._C_1 = -self._Pud * temp.LUsolve(f_v_jac_q)
+            else:
+                self._C_1 = zeros(o, n)
+            self._C_2 = (eye(o) - self._Pud *
+                    temp.LUsolve(f_v_jac_u)) * self._Pui
+        else:
+            self._C_1 = zeros(o, n)
+            self._C_2 = eye(o)
+
+    def _form_block_matrices(self):
+        """Form the block matrices for composing M, A, and B."""
+
+        # Extract dimension variables
+        l, m, n, o, s, k = self._dims
+        # Block Matrix Definitions. These are only defined if under certain
+        # conditions. If undefined, an empty matrix is used instead
+        if n != 0:
+            self._M_qq = self.f_0.jacobian(self._qd)
+            self._A_qq = -(self.f_0 + self.f_1).jacobian(self.q)
+        else:
+            self._M_qq = Matrix()
+            self._A_qq = Matrix()
+        if n != 0 and m != 0:
+            self._M_uqc = self.f_a.jacobian(self._qd_dup)
+            self._A_uqc = -self.f_a.jacobian(self.q)
+        else:
+            self._M_uqc = Matrix()
+            self._A_uqc = Matrix()
+        if n != 0 and o - m + k != 0:
+            self._M_uqd = self.f_3.jacobian(self._qd_dup)
+            self._A_uqd = -(self.f_2 + self.f_3 + self.f_4).jacobian(self.q)
+        else:
+            self._M_uqd = Matrix()
+            self._A_uqd = Matrix()
+        if o != 0 and m != 0:
+            self._M_uuc = self.f_a.jacobian(self._ud)
+            self._A_uuc = -self.f_a.jacobian(self.u)
+        else:
+            self._M_uuc = Matrix()
+            self._A_uuc = Matrix()
+        if o != 0 and o - m + k != 0:
+            self._M_uud = self.f_2.jacobian(self._ud)
+            self._A_uud = -(self.f_2 + self.f_3).jacobian(self.u)
+        else:
+            self._M_uud = Matrix()
+            self._A_uud = Matrix()
+        if o != 0 and n != 0:
+            self._A_qu = -self.f_1.jacobian(self.u)
+        else:
+            self._A_qu = Matrix()
+        if k != 0 and o - m + k != 0:
+            self._M_uld = self.f_4.jacobian(self.lams)
+        else:
+            self._M_uld = Matrix()
+        if s != 0 and o - m + k != 0:
+            self._B_u = -self.f_3.jacobian(self.r)
+        else:
+            self._B_u = Matrix()
+
+    def linearize(self, op_point=None, A_and_B=False, simplify=False):
+        """Linearize the system about the operating point. Note that
+        q_op, u_op, qd_op, ud_op must satisfy the equations of motion.
+        These may be either symbolic or numeric.
+
+        Parameters
+        ==========
+
+        op_point : dict or iterable of dicts, optional
+            Dictionary or iterable of dictionaries containing the operating
+            point conditions. These will be substituted in to the linearized
+            system before the linearization is complete. Leave blank if you
+            want a completely symbolic form. Note that any reduction in
+            symbols (whether substituted for numbers or expressions with a
+            common parameter) will result in faster runtime.
+
+        A_and_B : bool, optional
+            If A_and_B=False (default), (M, A, B) is returned for forming
+            [M]*[q, u]^T = [A]*[q_ind, u_ind]^T + [B]r. If A_and_B=True,
+            (A, B) is returned for forming dx = [A]x + [B]r, where
+            x = [q_ind, u_ind]^T.
+
+        simplify : bool, optional
+            Determines if returned values are simplified before return.
+            For large expressions this may be time consuming. Default is False.
+
+        Potential Issues
+        ================
+
+            Note that the process of solving with A_and_B=True is
+            computationally intensive if there are many symbolic parameters.
+            For this reason, it may be more desirable to use the default
+            A_and_B=False, returning M, A, and B. More values may then be
+            substituted in to these matrices later on. The state space form can
+            then be found as A = P.T*M.LUsolve(A), B = P.T*M.LUsolve(B), where
+            P = Linearizer.perm_mat.
+        """
+
+        # Run the setup if needed:
+        if not self._setup_done:
+            self._setup()
+
+        # Compose dict of operating conditions
+        if isinstance(op_point, dict):
+            op_point_dict = op_point
+        elif isinstance(op_point, Iterable):
+            op_point_dict = {}
+            for op in op_point:
+                op_point_dict.update(op)
+        else:
+            op_point_dict = {}
+
+        # Extract dimension variables
+        l, m, n, o, s, k = self._dims
+
+        # Rename terms to shorten expressions
+        M_qq = self._M_qq
+        M_uqc = self._M_uqc
+        M_uqd = self._M_uqd
+        M_uuc = self._M_uuc
+        M_uud = self._M_uud
+        M_uld = self._M_uld
+        A_qq = self._A_qq
+        A_uqc = self._A_uqc
+        A_uqd = self._A_uqd
+        A_qu = self._A_qu
+        A_uuc = self._A_uuc
+        A_uud = self._A_uud
+        B_u = self._B_u
+        C_0 = self._C_0
+        C_1 = self._C_1
+        C_2 = self._C_2
+
+        # Build up Mass Matrix
+        #     |M_qq    0_nxo   0_nxk|
+        # M = |M_uqc   M_uuc   0_mxk|
+        #     |M_uqd   M_uud   M_uld|
+        if o != 0:
+            col2 = Matrix([zeros(n, o), M_uuc, M_uud])
+        if k != 0:
+            col3 = Matrix([zeros(n + m, k), M_uld])
+        if n != 0:
+            col1 = Matrix([M_qq, M_uqc, M_uqd])
+            if o != 0 and k != 0:
+                M = col1.row_join(col2).row_join(col3)
+            elif o != 0:
+                M = col1.row_join(col2)
+            else:
+                M = col1
+        elif k != 0:
+            M = col2.row_join(col3)
+        else:
+            M = col2
+        M_eq = msubs(M, op_point_dict)
+
+        # Build up state coefficient matrix A
+        #     |(A_qq + A_qu*C_1)*C_0       A_qu*C_2|
+        # A = |(A_uqc + A_uuc*C_1)*C_0    A_uuc*C_2|
+        #     |(A_uqd + A_uud*C_1)*C_0    A_uud*C_2|
+        # Col 1 is only defined if n != 0
+        if n != 0:
+            r1c1 = A_qq
+            if o != 0:
+                r1c1 += (A_qu * C_1)
+            r1c1 = r1c1 * C_0
+            if m != 0:
+                r2c1 = A_uqc
+                if o != 0:
+                    r2c1 += (A_uuc * C_1)
+                r2c1 = r2c1 * C_0
+            else:
+                r2c1 = Matrix()
+            if o - m + k != 0:
+                r3c1 = A_uqd
+                if o != 0:
+                    r3c1 += (A_uud * C_1)
+                r3c1 = r3c1 * C_0
+            else:
+                r3c1 = Matrix()
+            col1 = Matrix([r1c1, r2c1, r3c1])
+        else:
+            col1 = Matrix()
+        # Col 2 is only defined if o != 0
+        if o != 0:
+            if n != 0:
+                r1c2 = A_qu * C_2
+            else:
+                r1c2 = Matrix()
+            if m != 0:
+                r2c2 = A_uuc * C_2
+            else:
+                r2c2 = Matrix()
+            if o - m + k != 0:
+                r3c2 = A_uud * C_2
+            else:
+                r3c2 = Matrix()
+            col2 = Matrix([r1c2, r2c2, r3c2])
+        else:
+            col2 = Matrix()
+        if col1:
+            if col2:
+                Amat = col1.row_join(col2)
+            else:
+                Amat = col1
+        else:
+            Amat = col2
+        Amat_eq = msubs(Amat, op_point_dict)
+
+        # Build up the B matrix if there are forcing variables
+        #     |0_(n + m)xs|
+        # B = |B_u        |
+        if s != 0 and o - m + k != 0:
+            Bmat = zeros(n + m, s).col_join(B_u)
+            Bmat_eq = msubs(Bmat, op_point_dict)
+        else:
+            Bmat_eq = Matrix()
+
+        # kwarg A_and_B indicates to return  A, B for forming the equation
+        # dx = [A]x + [B]r, where x = [q_indnd, u_indnd]^T,
+        if A_and_B:
+            A_cont = self.perm_mat.T * M_eq.LUsolve(Amat_eq)
+            if Bmat_eq:
+                B_cont = self.perm_mat.T * M_eq.LUsolve(Bmat_eq)
+            else:
+                # Bmat = Matrix([]), so no need to sub
+                B_cont = Bmat_eq
+            if simplify:
+                A_cont.simplify()
+                B_cont.simplify()
+            return A_cont, B_cont
+        # Otherwise return M, A, B for forming the equation
+        # [M]dx = [A]x + [B]r, where x = [q, u]^T
+        else:
+            if simplify:
+                M_eq.simplify()
+                Amat_eq.simplify()
+                Bmat_eq.simplify()
+            return M_eq, Amat_eq, Bmat_eq
+
+
+def permutation_matrix(orig_vec, per_vec):
+    """Compute the permutation matrix to change order of
+    orig_vec into order of per_vec.
+
+    Parameters
+    ==========
+
+    orig_vec : array_like
+        Symbols in original ordering.
+    per_vec : array_like
+        Symbols in new ordering.
+
+    Returns
+    =======
+
+    p_matrix : Matrix
+        Permutation matrix such that orig_vec == (p_matrix * per_vec).
+    """
+    if not isinstance(orig_vec, (list, tuple)):
+        orig_vec = flatten(orig_vec)
+    if not isinstance(per_vec, (list, tuple)):
+        per_vec = flatten(per_vec)
+    if set(orig_vec) != set(per_vec):
+        raise ValueError("orig_vec and per_vec must be the same length, " +
+                "and contain the same symbols.")
+    ind_list = [orig_vec.index(i) for i in per_vec]
+    p_matrix = zeros(len(orig_vec))
+    for i, j in enumerate(ind_list):
+        p_matrix[i, j] = 1
+    return p_matrix

venv/lib/python3.10/site-packages/sympy/physics/mechanics/method.py

@@ -0,0 +1,39 @@
+from abc import ABC, abstractmethod
+
+class _Methods(ABC):
+    """Abstract Base Class for all methods."""
+
+    @abstractmethod
+    def q(self):
+        pass
+
+    @abstractmethod
+    def u(self):
+        pass
+
+    @abstractmethod
+    def bodies(self):
+        pass
+
+    @abstractmethod
+    def loads(self):
+        pass
+
+    @abstractmethod
+    def mass_matrix(self):
+        pass
+
+    @abstractmethod
+    def forcing(self):
+        pass
+
+    @abstractmethod
+    def mass_matrix_full(self):
+        pass
+
+    @abstractmethod
+    def forcing_full(self):
+        pass
+
+    def _form_eoms(self):
+        raise NotImplementedError("Subclasses must implement this.")

venv/lib/python3.10/site-packages/sympy/physics/mechanics/models.py

@@ -0,0 +1,230 @@
+#!/usr/bin/env python
+"""This module contains some sample symbolic models used for testing and
+examples."""
+
+# Internal imports
+from sympy.core import backend as sm
+import sympy.physics.mechanics as me
+
+
+def multi_mass_spring_damper(n=1, apply_gravity=False,
+                             apply_external_forces=False):
+    r"""Returns a system containing the symbolic equations of motion and
+    associated variables for a simple multi-degree of freedom point mass,
+    spring, damper system with optional gravitational and external
+    specified forces. For example, a two mass system under the influence of
+    gravity and external forces looks like:
+
+    ::
+
+        ----------------
+         |     |     |   | g
+         \    | |    |   V
+      k0 /    --- c0 |
+         |     |     | x0, v0
+        ---------    V
+        |  m0   | -----
+        ---------    |
+         | |   |     |
+         \ v  | |    |
+      k1 / f0 --- c1 |
+         |     |     | x1, v1
+        ---------    V
+        |  m1   | -----
+        ---------
+           | f1
+           V
+
+    Parameters
+    ==========
+
+    n : integer
+        The number of masses in the serial chain.
+    apply_gravity : boolean
+        If true, gravity will be applied to each mass.
+    apply_external_forces : boolean
+        If true, a time varying external force will be applied to each mass.
+
+    Returns
+    =======
+
+    kane : sympy.physics.mechanics.kane.KanesMethod
+        A KanesMethod object.
+
+    """
+
+    mass = sm.symbols('m:{}'.format(n))
+    stiffness = sm.symbols('k:{}'.format(n))
+    damping = sm.symbols('c:{}'.format(n))
+
+    acceleration_due_to_gravity = sm.symbols('g')
+
+    coordinates = me.dynamicsymbols('x:{}'.format(n))
+    speeds = me.dynamicsymbols('v:{}'.format(n))
+    specifieds = me.dynamicsymbols('f:{}'.format(n))
+
+    ceiling = me.ReferenceFrame('N')
+    origin = me.Point('origin')
+    origin.set_vel(ceiling, 0)
+
+    points = [origin]
+    kinematic_equations = []
+    particles = []
+    forces = []
+
+    for i in range(n):
+
+        center = points[-1].locatenew('center{}'.format(i),
+                                      coordinates[i] * ceiling.x)
+        center.set_vel(ceiling, points[-1].vel(ceiling) +
+                       speeds[i] * ceiling.x)
+        points.append(center)
+
+        block = me.Particle('block{}'.format(i), center, mass[i])
+
+        kinematic_equations.append(speeds[i] - coordinates[i].diff())
+
+        total_force = (-stiffness[i] * coordinates[i] -
+                       damping[i] * speeds[i])
+        try:
+            total_force += (stiffness[i + 1] * coordinates[i + 1] +
+                            damping[i + 1] * speeds[i + 1])
+        except IndexError:  # no force from below on last mass
+            pass
+
+        if apply_gravity:
+            total_force += mass[i] * acceleration_due_to_gravity
+
+        if apply_external_forces:
+            total_force += specifieds[i]
+
+        forces.append((center, total_force * ceiling.x))
+
+        particles.append(block)
+
+    kane = me.KanesMethod(ceiling, q_ind=coordinates, u_ind=speeds,
+                          kd_eqs=kinematic_equations)
+    kane.kanes_equations(particles, forces)
+
+    return kane
+
+
+def n_link_pendulum_on_cart(n=1, cart_force=True, joint_torques=False):
+    r"""Returns the system containing the symbolic first order equations of
+    motion for a 2D n-link pendulum on a sliding cart under the influence of
+    gravity.
+
+    ::
+
+                  |
+         o    y   v
+          \ 0 ^   g
+           \  |
+          --\-|----
+          |  \|   |
+      F-> |   o --|---> x
+          |       |
+          ---------
+           o     o
+
+    Parameters
+    ==========
+
+    n : integer
+        The number of links in the pendulum.
+    cart_force : boolean, default=True
+        If true an external specified lateral force is applied to the cart.
+    joint_torques : boolean, default=False
+        If true joint torques will be added as specified inputs at each
+        joint.
+
+    Returns
+    =======
+
+    kane : sympy.physics.mechanics.kane.KanesMethod
+        A KanesMethod object.
+
+    Notes
+    =====
+
+    The degrees of freedom of the system are n + 1, i.e. one for each
+    pendulum link and one for the lateral motion of the cart.
+
+    M x' = F, where x = [u0, ..., un+1, q0, ..., qn+1]
+
+    The joint angles are all defined relative to the ground where the x axis
+    defines the ground line and the y axis points up. The joint torques are
+    applied between each adjacent link and the between the cart and the
+    lower link where a positive torque corresponds to positive angle.
+
+    """
+    if n <= 0:
+        raise ValueError('The number of links must be a positive integer.')
+
+    q = me.dynamicsymbols('q:{}'.format(n + 1))
+    u = me.dynamicsymbols('u:{}'.format(n + 1))
+
+    if joint_torques is True:
+        T = me.dynamicsymbols('T1:{}'.format(n + 1))
+
+    m = sm.symbols('m:{}'.format(n + 1))
+    l = sm.symbols('l:{}'.format(n))
+    g, t = sm.symbols('g t')
+
+    I = me.ReferenceFrame('I')
+    O = me.Point('O')
+    O.set_vel(I, 0)
+
+    P0 = me.Point('P0')
+    P0.set_pos(O, q[0] * I.x)
+    P0.set_vel(I, u[0] * I.x)
+    Pa0 = me.Particle('Pa0', P0, m[0])
+
+    frames = [I]
+    points = [P0]
+    particles = [Pa0]
+    forces = [(P0, -m[0] * g * I.y)]
+    kindiffs = [q[0].diff(t) - u[0]]
+
+    if cart_force is True or joint_torques is True:
+        specified = []
+    else:
+        specified = None
+
+    for i in range(n):
+        Bi = I.orientnew('B{}'.format(i), 'Axis', [q[i + 1], I.z])
+        Bi.set_ang_vel(I, u[i + 1] * I.z)
+        frames.append(Bi)
+
+        Pi = points[-1].locatenew('P{}'.format(i + 1), l[i] * Bi.y)
+        Pi.v2pt_theory(points[-1], I, Bi)
+        points.append(Pi)
+
+        Pai = me.Particle('Pa' + str(i + 1), Pi, m[i + 1])
+        particles.append(Pai)
+
+        forces.append((Pi, -m[i + 1] * g * I.y))
+
+        if joint_torques is True:
+
+            specified.append(T[i])
+
+            if i == 0:
+                forces.append((I, -T[i] * I.z))
+
+            if i == n - 1:
+                forces.append((Bi, T[i] * I.z))
+            else:
+                forces.append((Bi, T[i] * I.z - T[i + 1] * I.z))
+
+        kindiffs.append(q[i + 1].diff(t) - u[i + 1])
+
+    if cart_force is True:
+        F = me.dynamicsymbols('F')
+        forces.append((P0, F * I.x))
+        specified.append(F)
+
+    kane = me.KanesMethod(I, q_ind=q, u_ind=u, kd_eqs=kindiffs)
+    kane.kanes_equations(particles, forces)
+
+    return kane

venv/lib/python3.10/site-packages/sympy/physics/mechanics/particle.py

@@ -0,0 +1,281 @@
+from sympy.core.backend import sympify
+from sympy.physics.vector import Point
+
+from sympy.utilities.exceptions import sympy_deprecation_warning
+
+__all__ = ['Particle']
+
+
+class Particle:
+    """A particle.
+
+    Explanation
+    ===========
+
+    Particles have a non-zero mass and lack spatial extension; they take up no
+    space.
+
+    Values need to be supplied on initialization, but can be changed later.
+
+    Parameters
+    ==========
+
+    name : str
+        Name of particle
+    point : Point
+        A physics/mechanics Point which represents the position, velocity, and
+        acceleration of this Particle
+    mass : sympifyable
+        A SymPy expression representing the Particle's mass
+
+    Examples
+    ========
+
+    >>> from sympy.physics.mechanics import Particle, Point
+    >>> from sympy import Symbol
+    >>> po = Point('po')
+    >>> m = Symbol('m')
+    >>> pa = Particle('pa', po, m)
+    >>> # Or you could change these later
+    >>> pa.mass = m
+    >>> pa.point = po
+
+    """
+
+    def __init__(self, name, point, mass):
+        if not isinstance(name, str):
+            raise TypeError('Supply a valid name.')
+        self._name = name
+        self.mass = mass
+        self.point = point
+        self.potential_energy = 0
+
+    def __str__(self):
+        return self._name
+
+    def __repr__(self):
+        return self.__str__()
+
+    @property
+    def mass(self):
+        """Mass of the particle."""
+        return self._mass
+
+    @mass.setter
+    def mass(self, value):
+        self._mass = sympify(value)
+
+    @property
+    def point(self):
+        """Point of the particle."""
+        return self._point
+
+    @point.setter
+    def point(self, p):
+        if not isinstance(p, Point):
+            raise TypeError("Particle point attribute must be a Point object.")
+        self._point = p
+
+    def linear_momentum(self, frame):
+        """Linear momentum of the particle.
+
+        Explanation
+        ===========
+
+        The linear momentum L, of a particle P, with respect to frame N is
+        given by:
+
+        L = m * v
+
+        where m is the mass of the particle, and v is the velocity of the
+        particle in the frame N.
+
+        Parameters
+        ==========
+
+        frame : ReferenceFrame
+            The frame in which linear momentum is desired.
+
+        Examples
+        ========
+
+        >>> from sympy.physics.mechanics import Particle, Point, ReferenceFrame
+        >>> from sympy.physics.mechanics import dynamicsymbols
+        >>> from sympy.physics.vector import init_vprinting
+        >>> init_vprinting(pretty_print=False)
+        >>> m, v = dynamicsymbols('m v')
+        >>> N = ReferenceFrame('N')
+        >>> P = Point('P')
+        >>> A = Particle('A', P, m)
+        >>> P.set_vel(N, v * N.x)
+        >>> A.linear_momentum(N)
+        m*v*N.x
+
+        """
+
+        return self.mass * self.point.vel(frame)
+
+    def angular_momentum(self, point, frame):
+        """Angular momentum of the particle about the point.
+
+        Explanation
+        ===========
+
+        The angular momentum H, about some point O of a particle, P, is given
+        by:
+
+        ``H = cross(r, m * v)``
+
+        where r is the position vector from point O to the particle P, m is
+        the mass of the particle, and v is the velocity of the particle in
+        the inertial frame, N.
+
+        Parameters
+        ==========
+
+        point : Point
+            The point about which angular momentum of the particle is desired.
+
+        frame : ReferenceFrame
+            The frame in which angular momentum is desired.
+
+        Examples
+        ========
+
+        >>> from sympy.physics.mechanics import Particle, Point, ReferenceFrame
+        >>> from sympy.physics.mechanics import dynamicsymbols
+        >>> from sympy.physics.vector import init_vprinting
+        >>> init_vprinting(pretty_print=False)
+        >>> m, v, r = dynamicsymbols('m v r')
+        >>> N = ReferenceFrame('N')
+        >>> O = Point('O')
+        >>> A = O.locatenew('A', r * N.x)
+        >>> P = Particle('P', A, m)
+        >>> P.point.set_vel(N, v * N.y)
+        >>> P.angular_momentum(O, N)
+        m*r*v*N.z
+
+        """
+
+        return self.point.pos_from(point) ^ (self.mass * self.point.vel(frame))
+
+    def kinetic_energy(self, frame):
+        """Kinetic energy of the particle.
+
+        Explanation
+        ===========
+
+        The kinetic energy, T, of a particle, P, is given by:
+
+        ``T = 1/2 (dot(m * v, v))``
+
+        where m is the mass of particle P, and v is the velocity of the
+        particle in the supplied ReferenceFrame.
+
+        Parameters
+        ==========
+
+        frame : ReferenceFrame
+            The Particle's velocity is typically defined with respect to
+            an inertial frame but any relevant frame in which the velocity is
+            known can be supplied.
+
+        Examples
+        ========
+
+        >>> from sympy.physics.mechanics import Particle, Point, ReferenceFrame
+        >>> from sympy import symbols
+        >>> m, v, r = symbols('m v r')
+        >>> N = ReferenceFrame('N')
+        >>> O = Point('O')
+        >>> P = Particle('P', O, m)
+        >>> P.point.set_vel(N, v * N.y)
+        >>> P.kinetic_energy(N)
+        m*v**2/2
+
+        """
+
+        return (self.mass / sympify(2) * self.point.vel(frame) &
+                self.point.vel(frame))
+
+    @property
+    def potential_energy(self):
+        """The potential energy of the Particle.
+
+        Examples
+        ========
+
+        >>> from sympy.physics.mechanics import Particle, Point
+        >>> from sympy import symbols
+        >>> m, g, h = symbols('m g h')
+        >>> O = Point('O')
+        >>> P = Particle('P', O, m)
+        >>> P.potential_energy = m * g * h
+        >>> P.potential_energy
+        g*h*m
+
+        """
+
+        return self._pe
+
+    @potential_energy.setter
+    def potential_energy(self, scalar):
+        """Used to set the potential energy of the Particle.
+
+        Parameters
+        ==========
+
+        scalar : Sympifyable
+            The potential energy (a scalar) of the Particle.
+
+        Examples
+        ========
+
+        >>> from sympy.physics.mechanics import Particle, Point
+        >>> from sympy import symbols
+        >>> m, g, h = symbols('m g h')
+        >>> O = Point('O')
+        >>> P = Particle('P', O, m)
+        >>> P.potential_energy = m * g * h
+
+        """
+
+        self._pe = sympify(scalar)
+
+    def set_potential_energy(self, scalar):
+        sympy_deprecation_warning(
+            """
+The sympy.physics.mechanics.Particle.set_potential_energy()
+method is deprecated. Instead use
+
+    P.potential_energy = scalar
+            """,
+        deprecated_since_version="1.5",
+        active_deprecations_target="deprecated-set-potential-energy",
+        )
+        self.potential_energy = scalar
+
+    def parallel_axis(self, point, frame):
+        """Returns an inertia dyadic of the particle with respect to another
+        point and frame.
+
+        Parameters
+        ==========
+
+        point : sympy.physics.vector.Point
+            The point to express the inertia dyadic about.
+        frame : sympy.physics.vector.ReferenceFrame
+            The reference frame used to construct the dyadic.
+
+        Returns
+        =======
+
+        inertia : sympy.physics.vector.Dyadic
+            The inertia dyadic of the particle expressed about the provided
+            point and frame.
+
+        """
+        # circular import issue
+        from sympy.physics.mechanics import inertia_of_point_mass
+        return inertia_of_point_mass(self.mass, self.point.pos_from(point),
+                                     frame)

venv/lib/python3.10/site-packages/sympy/physics/mechanics/rigidbody.py

@@ -0,0 +1,366 @@
+from sympy.core.backend import sympify
+from sympy.physics.vector import Point, ReferenceFrame, Dyadic
+
+from sympy.utilities.exceptions import sympy_deprecation_warning
+
+__all__ = ['RigidBody']
+
+
+class RigidBody:
+    """An idealized rigid body.
+
+    Explanation
+    ===========
+
+    This is essentially a container which holds the various components which
+    describe a rigid body: a name, mass, center of mass, reference frame, and
+    inertia.
+
+    All of these need to be supplied on creation, but can be changed
+    afterwards.
+
+    Attributes
+    ==========
+
+    name : string
+        The body's name.
+    masscenter : Point
+        The point which represents the center of mass of the rigid body.
+    frame : ReferenceFrame
+        The ReferenceFrame which the rigid body is fixed in.
+    mass : Sympifyable
+        The body's mass.
+    inertia : (Dyadic, Point)
+        The body's inertia about a point; stored in a tuple as shown above.
+
+    Examples
+    ========
+
+    >>> from sympy import Symbol
+    >>> from sympy.physics.mechanics import ReferenceFrame, Point, RigidBody
+    >>> from sympy.physics.mechanics import outer
+    >>> m = Symbol('m')
+    >>> A = ReferenceFrame('A')
+    >>> P = Point('P')
+    >>> I = outer (A.x, A.x)
+    >>> inertia_tuple = (I, P)
+    >>> B = RigidBody('B', P, A, m, inertia_tuple)
+    >>> # Or you could change them afterwards
+    >>> m2 = Symbol('m2')
+    >>> B.mass = m2
+
+    """
+
+    def __init__(self, name, masscenter, frame, mass, inertia):
+        if not isinstance(name, str):
+            raise TypeError('Supply a valid name.')
+        self._name = name
+        self.masscenter = masscenter
+        self.mass = mass
+        self.frame = frame
+        self.inertia = inertia
+        self.potential_energy = 0
+
+    def __str__(self):
+        return self._name
+
+    def __repr__(self):
+        return self.__str__()
+
+    @property
+    def frame(self):
+        """The ReferenceFrame fixed to the body."""
+        return self._frame
+
+    @frame.setter
+    def frame(self, F):
+        if not isinstance(F, ReferenceFrame):
+            raise TypeError("RigidBody frame must be a ReferenceFrame object.")
+        self._frame = F
+
+    @property
+    def masscenter(self):
+        """The body's center of mass."""
+        return self._masscenter
+
+    @masscenter.setter
+    def masscenter(self, p):
+        if not isinstance(p, Point):
+            raise TypeError("RigidBody center of mass must be a Point object.")
+        self._masscenter = p
+
+    @property
+    def mass(self):
+        """The body's mass."""
+        return self._mass
+
+    @mass.setter
+    def mass(self, m):
+        self._mass = sympify(m)
+
+    @property
+    def inertia(self):
+        """The body's inertia about a point; stored as (Dyadic, Point)."""
+        return (self._inertia, self._inertia_point)
+
+    @inertia.setter
+    def inertia(self, I):
+        if not isinstance(I[0], Dyadic):
+            raise TypeError("RigidBody inertia must be a Dyadic object.")
+        if not isinstance(I[1], Point):
+            raise TypeError("RigidBody inertia must be about a Point.")
+        self._inertia = I[0]
+        self._inertia_point = I[1]
+        # have I S/O, want I S/S*
+        # I S/O = I S/S* + I S*/O; I S/S* = I S/O - I S*/O
+        # I_S/S* = I_S/O - I_S*/O
+        from sympy.physics.mechanics.functions import inertia_of_point_mass
+        I_Ss_O = inertia_of_point_mass(self.mass,
+                                       self.masscenter.pos_from(I[1]),
+                                       self.frame)
+        self._central_inertia = I[0] - I_Ss_O
+
+    @property
+    def central_inertia(self):
+        """The body's central inertia dyadic."""
+        return self._central_inertia
+
+    @central_inertia.setter
+    def central_inertia(self, I):
+        if not isinstance(I, Dyadic):
+            raise TypeError("RigidBody inertia must be a Dyadic object.")
+        self.inertia = (I, self.masscenter)
+
+    def linear_momentum(self, frame):
+        """ Linear momentum of the rigid body.
+
+        Explanation
+        ===========
+
+        The linear momentum L, of a rigid body B, with respect to frame N is
+        given by:
+
+        L = M * v*
+
+        where M is the mass of the rigid body and v* is the velocity of
+        the mass center of B in the frame, N.
+
+        Parameters
+        ==========
+
+        frame : ReferenceFrame
+            The frame in which linear momentum is desired.
+
+        Examples
+        ========
+
+        >>> from sympy.physics.mechanics import Point, ReferenceFrame, outer
+        >>> from sympy.physics.mechanics import RigidBody, dynamicsymbols
+        >>> from sympy.physics.vector import init_vprinting
+        >>> init_vprinting(pretty_print=False)
+        >>> M, v = dynamicsymbols('M v')
+        >>> N = ReferenceFrame('N')
+        >>> P = Point('P')
+        >>> P.set_vel(N, v * N.x)
+        >>> I = outer (N.x, N.x)
+        >>> Inertia_tuple = (I, P)
+        >>> B = RigidBody('B', P, N, M, Inertia_tuple)
+        >>> B.linear_momentum(N)
+        M*v*N.x
+
+        """
+
+        return self.mass * self.masscenter.vel(frame)
+
+    def angular_momentum(self, point, frame):
+        """Returns the angular momentum of the rigid body about a point in the
+        given frame.
+
+        Explanation
+        ===========
+
+        The angular momentum H of a rigid body B about some point O in a frame
+        N is given by:
+
+        ``H = dot(I, w) + cross(r, M * v)``
+
+        where I is the central inertia dyadic of B, w is the angular velocity
+        of body B in the frame, N, r is the position vector from point O to the
+        mass center of B, and v is the velocity of the mass center in the
+        frame, N.
+
+        Parameters
+        ==========
+
+        point : Point
+            The point about which angular momentum is desired.
+        frame : ReferenceFrame
+            The frame in which angular momentum is desired.
+
+        Examples
+        ========
+
+        >>> from sympy.physics.mechanics import Point, ReferenceFrame, outer
+        >>> from sympy.physics.mechanics import RigidBody, dynamicsymbols
+        >>> from sympy.physics.vector import init_vprinting
+        >>> init_vprinting(pretty_print=False)
+        >>> M, v, r, omega = dynamicsymbols('M v r omega')
+        >>> N = ReferenceFrame('N')
+        >>> b = ReferenceFrame('b')
+        >>> b.set_ang_vel(N, omega * b.x)
+        >>> P = Point('P')
+        >>> P.set_vel(N, 1 * N.x)
+        >>> I = outer(b.x, b.x)
+        >>> B = RigidBody('B', P, b, M, (I, P))
+        >>> B.angular_momentum(P, N)
+        omega*b.x
+
+        """
+        I = self.central_inertia
+        w = self.frame.ang_vel_in(frame)
+        m = self.mass
+        r = self.masscenter.pos_from(point)
+        v = self.masscenter.vel(frame)
+
+        return I.dot(w) + r.cross(m * v)
+
+    def kinetic_energy(self, frame):
+        """Kinetic energy of the rigid body.
+
+        Explanation
+        ===========
+
+        The kinetic energy, T, of a rigid body, B, is given by:
+
+        ``T = 1/2 * (dot(dot(I, w), w) + dot(m * v, v))``
+
+        where I and m are the central inertia dyadic and mass of rigid body B,
+        respectively, omega is the body's angular velocity and v is the
+        velocity of the body's mass center in the supplied ReferenceFrame.
+
+        Parameters
+        ==========
+
+        frame : ReferenceFrame
+            The RigidBody's angular velocity and the velocity of it's mass
+            center are typically defined with respect to an inertial frame but
+            any relevant frame in which the velocities are known can be supplied.
+
+        Examples
+        ========
+
+        >>> from sympy.physics.mechanics import Point, ReferenceFrame, outer
+        >>> from sympy.physics.mechanics import RigidBody
+        >>> from sympy import symbols
+        >>> M, v, r, omega = symbols('M v r omega')
+        >>> N = ReferenceFrame('N')
+        >>> b = ReferenceFrame('b')
+        >>> b.set_ang_vel(N, omega * b.x)
+        >>> P = Point('P')
+        >>> P.set_vel(N, v * N.x)
+        >>> I = outer (b.x, b.x)
+        >>> inertia_tuple = (I, P)
+        >>> B = RigidBody('B', P, b, M, inertia_tuple)
+        >>> B.kinetic_energy(N)
+        M*v**2/2 + omega**2/2
+
+        """
+
+        rotational_KE = (self.frame.ang_vel_in(frame) & (self.central_inertia &
+                self.frame.ang_vel_in(frame)) / sympify(2))
+
+        translational_KE = (self.mass * (self.masscenter.vel(frame) &
+            self.masscenter.vel(frame)) / sympify(2))
+
+        return rotational_KE + translational_KE
+
+    @property
+    def potential_energy(self):
+        """The potential energy of the RigidBody.
+
+        Examples
+        ========
+
+        >>> from sympy.physics.mechanics import RigidBody, Point, outer, ReferenceFrame
+        >>> from sympy import symbols
+        >>> M, g, h = symbols('M g h')
+        >>> b = ReferenceFrame('b')
+        >>> P = Point('P')
+        >>> I = outer (b.x, b.x)
+        >>> Inertia_tuple = (I, P)
+        >>> B = RigidBody('B', P, b, M, Inertia_tuple)
+        >>> B.potential_energy = M * g * h
+        >>> B.potential_energy
+        M*g*h
+
+        """
+
+        return self._pe
+
+    @potential_energy.setter
+    def potential_energy(self, scalar):
+        """Used to set the potential energy of this RigidBody.
+
+        Parameters
+        ==========
+
+        scalar: Sympifyable
+            The potential energy (a scalar) of the RigidBody.
+
+        Examples
+        ========
+
+        >>> from sympy.physics.mechanics import Point, outer
+        >>> from sympy.physics.mechanics import RigidBody, ReferenceFrame
+        >>> from sympy import symbols
+        >>> b = ReferenceFrame('b')
+        >>> M, g, h = symbols('M g h')
+        >>> P = Point('P')
+        >>> I = outer (b.x, b.x)
+        >>> Inertia_tuple = (I, P)
+        >>> B = RigidBody('B', P, b, M, Inertia_tuple)
+        >>> B.potential_energy = M * g * h
+
+        """
+
+        self._pe = sympify(scalar)
+
+    def set_potential_energy(self, scalar):
+        sympy_deprecation_warning(
+            """
+The sympy.physics.mechanics.RigidBody.set_potential_energy()
+method is deprecated. Instead use
+
+    B.potential_energy = scalar
+            """,
+        deprecated_since_version="1.5",
+        active_deprecations_target="deprecated-set-potential-energy",
+        )
+        self.potential_energy = scalar
+
+    def parallel_axis(self, point, frame=None):
+        """Returns the inertia dyadic of the body with respect to another
+        point.
+
+        Parameters
+        ==========
+
+        point : sympy.physics.vector.Point
+            The point to express the inertia dyadic about.
+        frame : sympy.physics.vector.ReferenceFrame
+            The reference frame used to construct the dyadic.
+
+        Returns
+        =======
+
+        inertia : sympy.physics.vector.Dyadic
+            The inertia dyadic of the rigid body expressed about the provided
+            point.
+
+        """
+        # circular import issue
+        from sympy.physics.mechanics.functions import inertia_of_point_mass
+        if frame is None:
+            frame = self.frame
+        return self.central_inertia + inertia_of_point_mass(
+            self.mass, self.masscenter.pos_from(point), frame)

venv/lib/python3.10/site-packages/sympy/physics/mechanics/system.py

@@ -0,0 +1,445 @@
+from sympy.core.backend import eye, Matrix, zeros
+from sympy.physics.mechanics import dynamicsymbols
+from sympy.physics.mechanics.functions import find_dynamicsymbols
+
+__all__ = ['SymbolicSystem']
+
+
+class SymbolicSystem:
+    """SymbolicSystem is a class that contains all the information about a
+    system in a symbolic format such as the equations of motions and the bodies
+    and loads in the system.
+
+    There are three ways that the equations of motion can be described for
+    Symbolic System:
+
+
+        [1] Explicit form where the kinematics and dynamics are combined
+            x' = F_1(x, t, r, p)
+
+        [2] Implicit form where the kinematics and dynamics are combined
+            M_2(x, p) x' = F_2(x, t, r, p)
+
+        [3] Implicit form where the kinematics and dynamics are separate
+            M_3(q, p) u' = F_3(q, u, t, r, p)
+            q' = G(q, u, t, r, p)
+
+    where
+
+    x : states, e.g. [q, u]
+    t : time
+    r : specified (exogenous) inputs
+    p : constants
+    q : generalized coordinates
+    u : generalized speeds
+    F_1 : right hand side of the combined equations in explicit form
+    F_2 : right hand side of the combined equations in implicit form
+    F_3 : right hand side of the dynamical equations in implicit form
+    M_2 : mass matrix of the combined equations in implicit form
+    M_3 : mass matrix of the dynamical equations in implicit form
+    G : right hand side of the kinematical differential equations
+
+        Parameters
+        ==========
+
+        coord_states : ordered iterable of functions of time
+            This input will either be a collection of the coordinates or states
+            of the system depending on whether or not the speeds are also
+            given. If speeds are specified this input will be assumed to
+            be the coordinates otherwise this input will be assumed to
+            be the states.
+
+        right_hand_side : Matrix
+            This variable is the right hand side of the equations of motion in
+            any of the forms. The specific form will be assumed depending on
+            whether a mass matrix or coordinate derivatives are given.
+
+        speeds : ordered iterable of functions of time, optional
+            This is a collection of the generalized speeds of the system. If
+            given it will be assumed that the first argument (coord_states)
+            will represent the generalized coordinates of the system.
+
+        mass_matrix : Matrix, optional
+            The matrix of the implicit forms of the equations of motion (forms
+            [2] and [3]). The distinction between the forms is determined by
+            whether or not the coordinate derivatives are passed in. If
+            they are given form [3] will be assumed otherwise form [2] is
+            assumed.
+
+        coordinate_derivatives : Matrix, optional
+            The right hand side of the kinematical equations in explicit form.
+            If given it will be assumed that the equations of motion are being
+            entered in form [3].
+
+        alg_con : Iterable, optional
+            The indexes of the rows in the equations of motion that contain
+            algebraic constraints instead of differential equations. If the
+            equations are input in form [3], it will be assumed the indexes are
+            referencing the mass_matrix/right_hand_side combination and not the
+            coordinate_derivatives.
+
+        output_eqns : Dictionary, optional
+            Any output equations that are desired to be tracked are stored in a
+            dictionary where the key corresponds to the name given for the
+            specific equation and the value is the equation itself in symbolic
+            form
+
+        coord_idxs : Iterable, optional
+            If coord_states corresponds to the states rather than the
+            coordinates this variable will tell SymbolicSystem which indexes of
+            the states correspond to generalized coordinates.
+
+        speed_idxs : Iterable, optional
+            If coord_states corresponds to the states rather than the
+            coordinates this variable will tell SymbolicSystem which indexes of
+            the states correspond to generalized speeds.
+
+        bodies : iterable of Body/Rigidbody objects, optional
+            Iterable containing the bodies of the system
+
+        loads : iterable of load instances (described below), optional
+            Iterable containing the loads of the system where forces are given
+            by (point of application, force vector) and torques are given by
+            (reference frame acting upon, torque vector). Ex [(point, force),
+            (ref_frame, torque)]
+
+    Attributes
+    ==========
+
+    coordinates : Matrix, shape(n, 1)
+        This is a matrix containing the generalized coordinates of the system
+
+    speeds : Matrix, shape(m, 1)
+        This is a matrix containing the generalized speeds of the system
+
+    states : Matrix, shape(o, 1)
+        This is a matrix containing the state variables of the system
+
+    alg_con : List
+        This list contains the indices of the algebraic constraints in the
+        combined equations of motion. The presence of these constraints
+        requires that a DAE solver be used instead of an ODE solver.
+        If the system is given in form [3] the alg_con variable will be
+        adjusted such that it is a representation of the combined kinematics
+        and dynamics thus make sure it always matches the mass matrix
+        entered.
+
+    dyn_implicit_mat : Matrix, shape(m, m)
+        This is the M matrix in form [3] of the equations of motion (the mass
+        matrix or generalized inertia matrix of the dynamical equations of
+        motion in implicit form).
+
+    dyn_implicit_rhs : Matrix, shape(m, 1)
+        This is the F vector in form [3] of the equations of motion (the right
+        hand side of the dynamical equations of motion in implicit form).
+
+    comb_implicit_mat : Matrix, shape(o, o)
+        This is the M matrix in form [2] of the equations of motion.
+        This matrix contains a block diagonal structure where the top
+        left block (the first rows) represent the matrix in the
+        implicit form of the kinematical equations and the bottom right
+        block (the last rows) represent the matrix in the implicit form
+        of the dynamical equations.
+
+    comb_implicit_rhs : Matrix, shape(o, 1)
+        This is the F vector in form [2] of the equations of motion. The top
+        part of the vector represents the right hand side of the implicit form
+        of the kinemaical equations and the bottom of the vector represents the
+        right hand side of the implicit form of the dynamical equations of
+        motion.
+
+    comb_explicit_rhs : Matrix, shape(o, 1)
+        This vector represents the right hand side of the combined equations of
+        motion in explicit form (form [1] from above).
+
+    kin_explicit_rhs : Matrix, shape(m, 1)
+        This is the right hand side of the explicit form of the kinematical
+        equations of motion as can be seen in form [3] (the G matrix).
+
+    output_eqns : Dictionary
+        If output equations were given they are stored in a dictionary where
+        the key corresponds to the name given for the specific equation and
+        the value is the equation itself in symbolic form
+
+    bodies : Tuple
+        If the bodies in the system were given they are stored in a tuple for
+        future access
+
+    loads : Tuple
+        If the loads in the system were given they are stored in a tuple for
+        future access. This includes forces and torques where forces are given
+        by (point of application, force vector) and torques are given by
+        (reference frame acted upon, torque vector).
+
+    Example
+    =======
+
+    As a simple example, the dynamics of a simple pendulum will be input into a
+    SymbolicSystem object manually. First some imports will be needed and then
+    symbols will be set up for the length of the pendulum (l), mass at the end
+    of the pendulum (m), and a constant for gravity (g). ::
+
+        >>> from sympy import Matrix, sin, symbols
+        >>> from sympy.physics.mechanics import dynamicsymbols, SymbolicSystem
+        >>> l, m, g = symbols('l m g')
+
+    The system will be defined by an angle of theta from the vertical and a
+    generalized speed of omega will be used where omega = theta_dot. ::
+
+        >>> theta, omega = dynamicsymbols('theta omega')
+
+    Now the equations of motion are ready to be formed and passed to the
+    SymbolicSystem object. ::
+
+        >>> kin_explicit_rhs = Matrix([omega])
+        >>> dyn_implicit_mat = Matrix([l**2 * m])
+        >>> dyn_implicit_rhs = Matrix([-g * l * m * sin(theta)])
+        >>> symsystem = SymbolicSystem([theta], dyn_implicit_rhs, [omega],
+        ...                            dyn_implicit_mat)
+
+    Notes
+    =====
+
+    m : number of generalized speeds
+    n : number of generalized coordinates
+    o : number of states
+
+    """
+
+    def __init__(self, coord_states, right_hand_side, speeds=None,
+                 mass_matrix=None, coordinate_derivatives=None, alg_con=None,
+                 output_eqns={}, coord_idxs=None, speed_idxs=None, bodies=None,
+                 loads=None):
+        """Initializes a SymbolicSystem object"""
+
+        # Extract information on speeds, coordinates and states
+        if speeds is None:
+            self._states = Matrix(coord_states)
+
+            if coord_idxs is None:
+                self._coordinates = None
+            else:
+                coords = [coord_states[i] for i in coord_idxs]
+                self._coordinates = Matrix(coords)
+
+            if speed_idxs is None:
+                self._speeds = None
+            else:
+                speeds_inter = [coord_states[i] for i in speed_idxs]
+                self._speeds = Matrix(speeds_inter)
+        else:
+            self._coordinates = Matrix(coord_states)
+            self._speeds = Matrix(speeds)
+            self._states = self._coordinates.col_join(self._speeds)
+
+        # Extract equations of motion form
+        if coordinate_derivatives is not None:
+            self._kin_explicit_rhs = coordinate_derivatives
+            self._dyn_implicit_rhs = right_hand_side
+            self._dyn_implicit_mat = mass_matrix
+            self._comb_implicit_rhs = None
+            self._comb_implicit_mat = None
+            self._comb_explicit_rhs = None
+        elif mass_matrix is not None:
+            self._kin_explicit_rhs = None
+            self._dyn_implicit_rhs = None
+            self._dyn_implicit_mat = None
+            self._comb_implicit_rhs = right_hand_side
+            self._comb_implicit_mat = mass_matrix
+            self._comb_explicit_rhs = None
+        else:
+            self._kin_explicit_rhs = None
+            self._dyn_implicit_rhs = None
+            self._dyn_implicit_mat = None
+            self._comb_implicit_rhs = None
+            self._comb_implicit_mat = None
+            self._comb_explicit_rhs = right_hand_side
+
+        # Set the remainder of the inputs as instance attributes
+        if alg_con is not None and coordinate_derivatives is not None:
+            alg_con = [i + len(coordinate_derivatives) for i in alg_con]
+        self._alg_con = alg_con
+        self.output_eqns = output_eqns
+
+        # Change the body and loads iterables to tuples if they are not tuples
+        # already
+        if not isinstance(bodies, tuple) and bodies is not None:
+            bodies = tuple(bodies)
+        if not isinstance(loads, tuple) and loads is not None:
+            loads = tuple(loads)
+        self._bodies = bodies
+        self._loads = loads
+
+    @property
+    def coordinates(self):
+        """Returns the column matrix of the generalized coordinates"""
+        if self._coordinates is None:
+            raise AttributeError("The coordinates were not specified.")
+        else:
+            return self._coordinates
+
+    @property
+    def speeds(self):
+        """Returns the column matrix of generalized speeds"""
+        if self._speeds is None:
+            raise AttributeError("The speeds were not specified.")
+        else:
+            return self._speeds
+
+    @property
+    def states(self):
+        """Returns the column matrix of the state variables"""
+        return self._states
+
+    @property
+    def alg_con(self):
+        """Returns a list with the indices of the rows containing algebraic
+        constraints in the combined form of the equations of motion"""
+        return self._alg_con
+
+    @property
+    def dyn_implicit_mat(self):
+        """Returns the matrix, M, corresponding to the dynamic equations in
+        implicit form, M x' = F, where the kinematical equations are not
+        included"""
+        if self._dyn_implicit_mat is None:
+            raise AttributeError("dyn_implicit_mat is not specified for "
+                                 "equations of motion form [1] or [2].")
+        else:
+            return self._dyn_implicit_mat
+
+    @property
+    def dyn_implicit_rhs(self):
+        """Returns the column matrix, F, corresponding to the dynamic equations
+        in implicit form, M x' = F, where the kinematical equations are not
+        included"""
+        if self._dyn_implicit_rhs is None:
+            raise AttributeError("dyn_implicit_rhs is not specified for "
+                                 "equations of motion form [1] or [2].")
+        else:
+            return self._dyn_implicit_rhs
+
+    @property
+    def comb_implicit_mat(self):
+        """Returns the matrix, M, corresponding to the equations of motion in
+        implicit form (form [2]), M x' = F, where the kinematical equations are
+        included"""
+        if self._comb_implicit_mat is None:
+            if self._dyn_implicit_mat is not None:
+                num_kin_eqns = len(self._kin_explicit_rhs)
+                num_dyn_eqns = len(self._dyn_implicit_rhs)
+                zeros1 = zeros(num_kin_eqns, num_dyn_eqns)
+                zeros2 = zeros(num_dyn_eqns, num_kin_eqns)
+                inter1 = eye(num_kin_eqns).row_join(zeros1)
+                inter2 = zeros2.row_join(self._dyn_implicit_mat)
+                self._comb_implicit_mat = inter1.col_join(inter2)
+                return self._comb_implicit_mat
+            else:
+                raise AttributeError("comb_implicit_mat is not specified for "
+                                     "equations of motion form [1].")
+        else:
+            return self._comb_implicit_mat
+
+    @property
+    def comb_implicit_rhs(self):
+        """Returns the column matrix, F, corresponding to the equations of
+        motion in implicit form (form [2]), M x' = F, where the kinematical
+        equations are included"""
+        if self._comb_implicit_rhs is None:
+            if self._dyn_implicit_rhs is not None:
+                kin_inter = self._kin_explicit_rhs
+                dyn_inter = self._dyn_implicit_rhs
+                self._comb_implicit_rhs = kin_inter.col_join(dyn_inter)
+                return self._comb_implicit_rhs
+            else:
+                raise AttributeError("comb_implicit_mat is not specified for "
+                                     "equations of motion in form [1].")
+        else:
+            return self._comb_implicit_rhs
+
+    def compute_explicit_form(self):
+        """If the explicit right hand side of the combined equations of motion
+        is to provided upon initialization, this method will calculate it. This
+        calculation can potentially take awhile to compute."""
+        if self._comb_explicit_rhs is not None:
+            raise AttributeError("comb_explicit_rhs is already formed.")
+
+        inter1 = getattr(self, 'kin_explicit_rhs', None)
+        if inter1 is not None:
+            inter2 = self._dyn_implicit_mat.LUsolve(self._dyn_implicit_rhs)
+            out = inter1.col_join(inter2)
+        else:
+            out = self._comb_implicit_mat.LUsolve(self._comb_implicit_rhs)
+
+        self._comb_explicit_rhs = out
+
+    @property
+    def comb_explicit_rhs(self):
+        """Returns the right hand side of the equations of motion in explicit
+        form, x' = F, where the kinematical equations are included"""
+        if self._comb_explicit_rhs is None:
+            raise AttributeError("Please run .combute_explicit_form before "
+                                 "attempting to access comb_explicit_rhs.")
+        else:
+            return self._comb_explicit_rhs
+
+    @property
+    def kin_explicit_rhs(self):
+        """Returns the right hand side of the kinematical equations in explicit
+        form, q' = G"""
+        if self._kin_explicit_rhs is None:
+            raise AttributeError("kin_explicit_rhs is not specified for "
+                                 "equations of motion form [1] or [2].")
+        else:
+            return self._kin_explicit_rhs
+
+    def dynamic_symbols(self):
+        """Returns a column matrix containing all of the symbols in the system
+        that depend on time"""
+        # Create a list of all of the expressions in the equations of motion
+        if self._comb_explicit_rhs is None:
+            eom_expressions = (self.comb_implicit_mat[:] +
+                               self.comb_implicit_rhs[:])
+        else:
+            eom_expressions = (self._comb_explicit_rhs[:])
+
+        functions_of_time = set()
+        for expr in eom_expressions:
+            functions_of_time = functions_of_time.union(
+                find_dynamicsymbols(expr))
+        functions_of_time = functions_of_time.union(self._states)
+
+        return tuple(functions_of_time)
+
+    def constant_symbols(self):
+        """Returns a column matrix containing all of the symbols in the system
+        that do not depend on time"""
+        # Create a list of all of the expressions in the equations of motion
+        if self._comb_explicit_rhs is None:
+            eom_expressions = (self.comb_implicit_mat[:] +
+                               self.comb_implicit_rhs[:])
+        else:
+            eom_expressions = (self._comb_explicit_rhs[:])
+
+        constants = set()
+        for expr in eom_expressions:
+            constants = constants.union(expr.free_symbols)
+        constants.remove(dynamicsymbols._t)
+
+        return tuple(constants)
+
+    @property
+    def bodies(self):
+        """Returns the bodies in the system"""
+        if self._bodies is None:
+            raise AttributeError("bodies were not specified for the system.")
+        else:
+            return self._bodies
+
+    @property
+    def loads(self):
+        """Returns the loads in the system"""
+        if self._loads is None:
+            raise AttributeError("loads were not specified for the system.")
+        else:
+            return self._loads

venv/lib/python3.10/site-packages/sympy/physics/mechanics/tests/test_body.py

@@ -0,0 +1,319 @@
+from sympy.core.backend import (Symbol, symbols, sin, cos, Matrix, zeros,
+                                _simplify_matrix)
+from sympy.physics.vector import Point, ReferenceFrame, dynamicsymbols, Dyadic
+from sympy.physics.mechanics import inertia, Body
+from sympy.testing.pytest import raises
+
+
+def test_default():
+    body = Body('body')
+    assert body.name == 'body'
+    assert body.loads == []
+    point = Point('body_masscenter')
+    point.set_vel(body.frame, 0)
+    com = body.masscenter
+    frame = body.frame
+    assert com.vel(frame) == point.vel(frame)
+    assert body.mass == Symbol('body_mass')
+    ixx, iyy, izz = symbols('body_ixx body_iyy body_izz')
+    ixy, iyz, izx = symbols('body_ixy body_iyz body_izx')
+    assert body.inertia == (inertia(body.frame, ixx, iyy, izz, ixy, iyz, izx),
+                            body.masscenter)
+
+
+def test_custom_rigid_body():
+    # Body with RigidBody.
+    rigidbody_masscenter = Point('rigidbody_masscenter')
+    rigidbody_mass = Symbol('rigidbody_mass')
+    rigidbody_frame = ReferenceFrame('rigidbody_frame')
+    body_inertia = inertia(rigidbody_frame, 1, 0, 0)
+    rigid_body = Body('rigidbody_body', rigidbody_masscenter, rigidbody_mass,
+                      rigidbody_frame, body_inertia)
+    com = rigid_body.masscenter
+    frame = rigid_body.frame
+    rigidbody_masscenter.set_vel(rigidbody_frame, 0)
+    assert com.vel(frame) == rigidbody_masscenter.vel(frame)
+    assert com.pos_from(com) == rigidbody_masscenter.pos_from(com)
+
+    assert rigid_body.mass == rigidbody_mass
+    assert rigid_body.inertia == (body_inertia, rigidbody_masscenter)
+
+    assert rigid_body.is_rigidbody
+
+    assert hasattr(rigid_body, 'masscenter')
+    assert hasattr(rigid_body, 'mass')
+    assert hasattr(rigid_body, 'frame')
+    assert hasattr(rigid_body, 'inertia')
+
+
+def test_particle_body():
+    #  Body with Particle
+    particle_masscenter = Point('particle_masscenter')
+    particle_mass = Symbol('particle_mass')
+    particle_frame = ReferenceFrame('particle_frame')
+    particle_body = Body('particle_body', particle_masscenter, particle_mass,
+                         particle_frame)
+    com = particle_body.masscenter
+    frame = particle_body.frame
+    particle_masscenter.set_vel(particle_frame, 0)
+    assert com.vel(frame) == particle_masscenter.vel(frame)
+    assert com.pos_from(com) == particle_masscenter.pos_from(com)
+
+    assert particle_body.mass == particle_mass
+    assert not hasattr(particle_body, "_inertia")
+    assert hasattr(particle_body, 'frame')
+    assert hasattr(particle_body, 'masscenter')
+    assert hasattr(particle_body, 'mass')
+    assert particle_body.inertia == (Dyadic(0), particle_body.masscenter)
+    assert particle_body.central_inertia == Dyadic(0)
+    assert not particle_body.is_rigidbody
+
+    particle_body.central_inertia = inertia(particle_frame, 1, 1, 1)
+    assert particle_body.central_inertia == inertia(particle_frame, 1, 1, 1)
+    assert particle_body.is_rigidbody
+
+    particle_body = Body('particle_body', mass=particle_mass)
+    assert not particle_body.is_rigidbody
+    point = particle_body.masscenter.locatenew('point', particle_body.x)
+    point_inertia = particle_mass * inertia(particle_body.frame, 0, 1, 1)
+    particle_body.inertia = (point_inertia, point)
+    assert particle_body.inertia == (point_inertia, point)
+    assert particle_body.central_inertia == Dyadic(0)
+    assert particle_body.is_rigidbody
+
+
+def test_particle_body_add_force():
+    #  Body with Particle
+    particle_masscenter = Point('particle_masscenter')
+    particle_mass = Symbol('particle_mass')
+    particle_frame = ReferenceFrame('particle_frame')
+    particle_body = Body('particle_body', particle_masscenter, particle_mass,
+                         particle_frame)
+
+    a = Symbol('a')
+    force_vector = a * particle_body.frame.x
+    particle_body.apply_force(force_vector, particle_body.masscenter)
+    assert len(particle_body.loads) == 1
+    point = particle_body.masscenter.locatenew(
+        particle_body._name + '_point0', 0)
+    point.set_vel(particle_body.frame, 0)
+    force_point = particle_body.loads[0][0]
+
+    frame = particle_body.frame
+    assert force_point.vel(frame) == point.vel(frame)
+    assert force_point.pos_from(force_point) == point.pos_from(force_point)
+
+    assert particle_body.loads[0][1] == force_vector
+
+
+def test_body_add_force():
+    # Body with RigidBody.
+    rigidbody_masscenter = Point('rigidbody_masscenter')
+    rigidbody_mass = Symbol('rigidbody_mass')
+    rigidbody_frame = ReferenceFrame('rigidbody_frame')
+    body_inertia = inertia(rigidbody_frame, 1, 0, 0)
+    rigid_body = Body('rigidbody_body', rigidbody_masscenter, rigidbody_mass,
+                      rigidbody_frame, body_inertia)
+
+    l = Symbol('l')
+    Fa = Symbol('Fa')
+    point = rigid_body.masscenter.locatenew(
+        'rigidbody_body_point0',
+        l * rigid_body.frame.x)
+    point.set_vel(rigid_body.frame, 0)
+    force_vector = Fa * rigid_body.frame.z
+    # apply_force with point
+    rigid_body.apply_force(force_vector, point)
+    assert len(rigid_body.loads) == 1
+    force_point = rigid_body.loads[0][0]
+    frame = rigid_body.frame
+    assert force_point.vel(frame) == point.vel(frame)
+    assert force_point.pos_from(force_point) == point.pos_from(force_point)
+    assert rigid_body.loads[0][1] == force_vector
+    # apply_force without point
+    rigid_body.apply_force(force_vector)
+    assert len(rigid_body.loads) == 2
+    assert rigid_body.loads[1][1] == force_vector
+    # passing something else than point
+    raises(TypeError, lambda: rigid_body.apply_force(force_vector,  0))
+    raises(TypeError, lambda: rigid_body.apply_force(0))
+
+def test_body_add_torque():
+    body = Body('body')
+    torque_vector = body.frame.x
+    body.apply_torque(torque_vector)
+
+    assert len(body.loads) == 1
+    assert body.loads[0] == (body.frame, torque_vector)
+    raises(TypeError, lambda: body.apply_torque(0))
+
+def test_body_masscenter_vel():
+    A = Body('A')
+    N = ReferenceFrame('N')
+    B = Body('B', frame=N)
+    A.masscenter.set_vel(N, N.z)
+    assert A.masscenter_vel(B) == N.z
+    assert A.masscenter_vel(N) == N.z
+
+def test_body_ang_vel():
+    A = Body('A')
+    N = ReferenceFrame('N')
+    B = Body('B', frame=N)
+    A.frame.set_ang_vel(N, N.y)
+    assert A.ang_vel_in(B) == N.y
+    assert B.ang_vel_in(A) == -N.y
+    assert A.ang_vel_in(N) == N.y
+
+def test_body_dcm():
+    A = Body('A')
+    B = Body('B')
+    A.frame.orient_axis(B.frame, B.frame.z, 10)
+    assert A.dcm(B) == Matrix([[cos(10), sin(10), 0], [-sin(10), cos(10), 0], [0, 0, 1]])
+    assert A.dcm(B.frame) == Matrix([[cos(10), sin(10), 0], [-sin(10), cos(10), 0], [0, 0, 1]])
+
+def test_body_axis():
+    N = ReferenceFrame('N')
+    B = Body('B', frame=N)
+    assert B.x == N.x
+    assert B.y == N.y
+    assert B.z == N.z
+
+def test_apply_force_multiple_one_point():
+    a, b = symbols('a b')
+    P = Point('P')
+    B = Body('B')
+    f1 = a*B.x
+    f2 = b*B.y
+    B.apply_force(f1, P)
+    assert B.loads == [(P, f1)]
+    B.apply_force(f2, P)
+    assert B.loads == [(P, f1+f2)]
+
+def test_apply_force():
+    f, g = symbols('f g')
+    q, x, v1, v2 = dynamicsymbols('q x v1 v2')
+    P1 = Point('P1')
+    P2 = Point('P2')
+    B1 = Body('B1')
+    B2 = Body('B2')
+    N = ReferenceFrame('N')
+
+    P1.set_vel(B1.frame, v1*B1.x)
+    P2.set_vel(B2.frame, v2*B2.x)
+    force = f*q*N.z # time varying force
+
+    B1.apply_force(force, P1, B2, P2) #applying equal and opposite force on moving points
+    assert B1.loads == [(P1, force)]
+    assert B2.loads == [(P2, -force)]
+
+    g1 = B1.mass*g*N.y
+    g2 = B2.mass*g*N.y
+
+    B1.apply_force(g1) #applying gravity on B1 masscenter
+    B2.apply_force(g2) #applying gravity on B2 masscenter
+
+    assert B1.loads == [(P1,force), (B1.masscenter, g1)]
+    assert B2.loads == [(P2, -force), (B2.masscenter, g2)]
+
+    force2 = x*N.x
+
+    B1.apply_force(force2, reaction_body=B2) #Applying time varying force on masscenter
+
+    assert B1.loads == [(P1, force), (B1.masscenter, force2+g1)]
+    assert B2.loads == [(P2, -force), (B2.masscenter, -force2+g2)]
+
+def test_apply_torque():
+    t = symbols('t')
+    q = dynamicsymbols('q')
+    B1 = Body('B1')
+    B2 = Body('B2')
+    N = ReferenceFrame('N')
+    torque = t*q*N.x
+
+    B1.apply_torque(torque, B2) #Applying equal and opposite torque
+    assert B1.loads == [(B1.frame, torque)]
+    assert B2.loads == [(B2.frame, -torque)]
+
+    torque2 = t*N.y
+    B1.apply_torque(torque2)
+    assert B1.loads == [(B1.frame, torque+torque2)]
+
+def test_clear_load():
+    a = symbols('a')
+    P = Point('P')
+    B = Body('B')
+    force = a*B.z
+    B.apply_force(force, P)
+    assert B.loads == [(P, force)]
+    B.clear_loads()
+    assert B.loads == []
+
+def test_remove_load():
+    P1 = Point('P1')
+    P2 = Point('P2')
+    B = Body('B')
+    f1 = B.x
+    f2 = B.y
+    B.apply_force(f1, P1)
+    B.apply_force(f2, P2)
+    assert B.loads == [(P1, f1), (P2, f2)]
+    B.remove_load(P2)
+    assert B.loads == [(P1, f1)]
+    B.apply_torque(f1.cross(f2))
+    assert B.loads == [(P1, f1), (B.frame, f1.cross(f2))]
+    B.remove_load()
+    assert B.loads == [(P1, f1)]
+
+def test_apply_loads_on_multi_degree_freedom_holonomic_system():
+    """Example based on: https://pydy.readthedocs.io/en/latest/examples/multidof-holonomic.html"""
+    W = Body('W') #Wall
+    B = Body('B') #Block
+    P = Body('P') #Pendulum
+    b = Body('b') #bob
+    q1, q2 = dynamicsymbols('q1 q2') #generalized coordinates
+    k, c, g, kT = symbols('k c g kT') #constants
+    F, T = dynamicsymbols('F T') #Specified forces
+
+    #Applying forces
+    B.apply_force(F*W.x)
+    W.apply_force(k*q1*W.x, reaction_body=B) #Spring force
+    W.apply_force(c*q1.diff()*W.x, reaction_body=B) #dampner
+    P.apply_force(P.mass*g*W.y)
+    b.apply_force(b.mass*g*W.y)
+
+    #Applying torques
+    P.apply_torque(kT*q2*W.z, reaction_body=b)
+    P.apply_torque(T*W.z)
+
+    assert B.loads == [(B.masscenter, (F - k*q1 - c*q1.diff())*W.x)]
+    assert P.loads == [(P.masscenter, P.mass*g*W.y), (P.frame, (T + kT*q2)*W.z)]
+    assert b.loads == [(b.masscenter, b.mass*g*W.y), (b.frame, -kT*q2*W.z)]
+    assert W.loads == [(W.masscenter, (c*q1.diff() + k*q1)*W.x)]
+
+
+def test_parallel_axis():
+    N = ReferenceFrame('N')
+    m, Ix, Iy, Iz, a, b = symbols('m, I_x, I_y, I_z, a, b')
+    Io = inertia(N, Ix, Iy, Iz)
+    # Test RigidBody
+    o = Point('o')
+    p = o.locatenew('p', a * N.x + b * N.y)
+    R = Body('R', masscenter=o, frame=N, mass=m, central_inertia=Io)
+    Ip = R.parallel_axis(p)
+    Ip_expected = inertia(N, Ix + m * b**2, Iy + m * a**2,
+                          Iz + m * (a**2 + b**2), ixy=-m * a * b)
+    assert Ip == Ip_expected
+    # Reference frame from which the parallel axis is viewed should not matter
+    A = ReferenceFrame('A')
+    A.orient_axis(N, N.z, 1)
+    assert _simplify_matrix(
+        (R.parallel_axis(p, A) - Ip_expected).to_matrix(A)) == zeros(3, 3)
+    # Test Particle
+    o = Point('o')
+    p = o.locatenew('p', a * N.x + b * N.y)
+    P = Body('P', masscenter=o, mass=m, frame=N)
+    Ip = P.parallel_axis(p, N)
+    Ip_expected = inertia(N, m * b ** 2, m * a ** 2, m * (a ** 2 + b ** 2),
+                          ixy=-m * a * b)
+    assert not P.is_rigidbody
+    assert Ip == Ip_expected

venv/lib/python3.10/site-packages/sympy/physics/mechanics/tests/test_functions.py

@@ -0,0 +1,292 @@
+from sympy.core.backend import sin, cos, tan, pi, symbols, Matrix, S, Function
+from sympy.physics.mechanics import (Particle, Point, ReferenceFrame,
+                                     RigidBody)
+from sympy.physics.mechanics import (angular_momentum, dynamicsymbols,
+                                     inertia, inertia_of_point_mass,
+                                     kinetic_energy, linear_momentum,
+                                     outer, potential_energy, msubs,
+                                     find_dynamicsymbols, Lagrangian)
+
+from sympy.physics.mechanics.functions import (gravity, center_of_mass,
+                                               _validate_coordinates)
+from sympy.testing.pytest import raises
+
+
+q1, q2, q3, q4, q5 = symbols('q1 q2 q3 q4 q5')
+N = ReferenceFrame('N')
+A = N.orientnew('A', 'Axis', [q1, N.z])
+B = A.orientnew('B', 'Axis', [q2, A.x])
+C = B.orientnew('C', 'Axis', [q3, B.y])
+
+
+def test_inertia():
+    N = ReferenceFrame('N')
+    ixx, iyy, izz = symbols('ixx iyy izz')
+    ixy, iyz, izx = symbols('ixy iyz izx')
+    assert inertia(N, ixx, iyy, izz) == (ixx * (N.x | N.x) + iyy *
+            (N.y | N.y) + izz * (N.z | N.z))
+    assert inertia(N, 0, 0, 0) == 0 * (N.x | N.x)
+    raises(TypeError, lambda: inertia(0, 0, 0, 0))
+    assert inertia(N, ixx, iyy, izz, ixy, iyz, izx) == (ixx * (N.x | N.x) +
+            ixy * (N.x | N.y) + izx * (N.x | N.z) + ixy * (N.y | N.x) + iyy *
+        (N.y | N.y) + iyz * (N.y | N.z) + izx * (N.z | N.x) + iyz * (N.z |
+            N.y) + izz * (N.z | N.z))
+
+
+def test_inertia_of_point_mass():
+    r, s, t, m = symbols('r s t m')
+    N = ReferenceFrame('N')
+
+    px = r * N.x
+    I = inertia_of_point_mass(m, px, N)
+    assert I == m * r**2 * (N.y | N.y) + m * r**2 * (N.z | N.z)
+
+    py = s * N.y
+    I = inertia_of_point_mass(m, py, N)
+    assert I == m * s**2 * (N.x | N.x) + m * s**2 * (N.z | N.z)
+
+    pz = t * N.z
+    I = inertia_of_point_mass(m, pz, N)
+    assert I == m * t**2 * (N.x | N.x) + m * t**2 * (N.y | N.y)
+
+    p = px + py + pz
+    I = inertia_of_point_mass(m, p, N)
+    assert I == (m * (s**2 + t**2) * (N.x | N.x) -
+                 m * r * s * (N.x | N.y) -
+                 m * r * t * (N.x | N.z) -
+                 m * r * s * (N.y | N.x) +
+                 m * (r**2 + t**2) * (N.y | N.y) -
+                 m * s * t * (N.y | N.z) -
+                 m * r * t * (N.z | N.x) -
+                 m * s * t * (N.z | N.y) +
+                 m * (r**2 + s**2) * (N.z | N.z))
+
+
+def test_linear_momentum():
+    N = ReferenceFrame('N')
+    Ac = Point('Ac')
+    Ac.set_vel(N, 25 * N.y)
+    I = outer(N.x, N.x)
+    A = RigidBody('A', Ac, N, 20, (I, Ac))
+    P = Point('P')
+    Pa = Particle('Pa', P, 1)
+    Pa.point.set_vel(N, 10 * N.x)
+    raises(TypeError, lambda: linear_momentum(A, A, Pa))
+    raises(TypeError, lambda: linear_momentum(N, N, Pa))
+    assert linear_momentum(N, A, Pa) == 10 * N.x + 500 * N.y
+
+
+def test_angular_momentum_and_linear_momentum():
+    """A rod with length 2l, centroidal inertia I, and mass M along with a
+    particle of mass m fixed to the end of the rod rotate with an angular rate
+    of omega about point O which is fixed to the non-particle end of the rod.
+    The rod's reference frame is A and the inertial frame is N."""
+    m, M, l, I = symbols('m, M, l, I')
+    omega = dynamicsymbols('omega')
+    N = ReferenceFrame('N')
+    a = ReferenceFrame('a')
+    O = Point('O')
+    Ac = O.locatenew('Ac', l * N.x)
+    P = Ac.locatenew('P', l * N.x)
+    O.set_vel(N, 0 * N.x)
+    a.set_ang_vel(N, omega * N.z)
+    Ac.v2pt_theory(O, N, a)
+    P.v2pt_theory(O, N, a)
+    Pa = Particle('Pa', P, m)
+    A = RigidBody('A', Ac, a, M, (I * outer(N.z, N.z), Ac))
+    expected = 2 * m * omega * l * N.y + M * l * omega * N.y
+    assert linear_momentum(N, A, Pa) == expected
+    raises(TypeError, lambda: angular_momentum(N, N, A, Pa))
+    raises(TypeError, lambda: angular_momentum(O, O, A, Pa))
+    raises(TypeError, lambda: angular_momentum(O, N, O, Pa))
+    expected = (I + M * l**2 + 4 * m * l**2) * omega * N.z
+    assert angular_momentum(O, N, A, Pa) == expected
+
+
+def test_kinetic_energy():
+    m, M, l1 = symbols('m M l1')
+    omega = dynamicsymbols('omega')
+    N = ReferenceFrame('N')
+    O = Point('O')
+    O.set_vel(N, 0 * N.x)
+    Ac = O.locatenew('Ac', l1 * N.x)
+    P = Ac.locatenew('P', l1 * N.x)
+    a = ReferenceFrame('a')
+    a.set_ang_vel(N, omega * N.z)
+    Ac.v2pt_theory(O, N, a)
+    P.v2pt_theory(O, N, a)
+    Pa = Particle('Pa', P, m)
+    I = outer(N.z, N.z)
+    A = RigidBody('A', Ac, a, M, (I, Ac))
+    raises(TypeError, lambda: kinetic_energy(Pa, Pa, A))
+    raises(TypeError, lambda: kinetic_energy(N, N, A))
+    assert 0 == (kinetic_energy(N, Pa, A) - (M*l1**2*omega**2/2
+            + 2*l1**2*m*omega**2 + omega**2/2)).expand()
+
+
+def test_potential_energy():
+    m, M, l1, g, h, H = symbols('m M l1 g h H')
+    omega = dynamicsymbols('omega')
+    N = ReferenceFrame('N')
+    O = Point('O')
+    O.set_vel(N, 0 * N.x)
+    Ac = O.locatenew('Ac', l1 * N.x)
+    P = Ac.locatenew('P', l1 * N.x)
+    a = ReferenceFrame('a')
+    a.set_ang_vel(N, omega * N.z)
+    Ac.v2pt_theory(O, N, a)
+    P.v2pt_theory(O, N, a)
+    Pa = Particle('Pa', P, m)
+    I = outer(N.z, N.z)
+    A = RigidBody('A', Ac, a, M, (I, Ac))
+    Pa.potential_energy = m * g * h
+    A.potential_energy = M * g * H
+    assert potential_energy(A, Pa) == m * g * h + M * g * H
+
+
+def test_Lagrangian():
+    M, m, g, h = symbols('M m g h')
+    N = ReferenceFrame('N')
+    O = Point('O')
+    O.set_vel(N, 0 * N.x)
+    P = O.locatenew('P', 1 * N.x)
+    P.set_vel(N, 10 * N.x)
+    Pa = Particle('Pa', P, 1)
+    Ac = O.locatenew('Ac', 2 * N.y)
+    Ac.set_vel(N, 5 * N.y)
+    a = ReferenceFrame('a')
+    a.set_ang_vel(N, 10 * N.z)
+    I = outer(N.z, N.z)
+    A = RigidBody('A', Ac, a, 20, (I, Ac))
+    Pa.potential_energy = m * g * h
+    A.potential_energy = M * g * h
+    raises(TypeError, lambda: Lagrangian(A, A, Pa))
+    raises(TypeError, lambda: Lagrangian(N, N, Pa))
+
+
+def test_msubs():
+    a, b = symbols('a, b')
+    x, y, z = dynamicsymbols('x, y, z')
+    # Test simple substitution
+    expr = Matrix([[a*x + b, x*y.diff() + y],
+                   [x.diff().diff(), z + sin(z.diff())]])
+    sol = Matrix([[a + b, y],
+                  [x.diff().diff(), 1]])
+    sd = {x: 1, z: 1, z.diff(): 0, y.diff(): 0}
+    assert msubs(expr, sd) == sol
+    # Test smart substitution
+    expr = cos(x + y)*tan(x + y) + b*x.diff()
+    sd = {x: 0, y: pi/2, x.diff(): 1}
+    assert msubs(expr, sd, smart=True) == b + 1
+    N = ReferenceFrame('N')
+    v = x*N.x + y*N.y
+    d = x*(N.x|N.x) + y*(N.y|N.y)
+    v_sol = 1*N.y
+    d_sol = 1*(N.y|N.y)
+    sd = {x: 0, y: 1}
+    assert msubs(v, sd) == v_sol
+    assert msubs(d, sd) == d_sol
+
+
+def test_find_dynamicsymbols():
+    a, b = symbols('a, b')
+    x, y, z = dynamicsymbols('x, y, z')
+    expr = Matrix([[a*x + b, x*y.diff() + y],
+                   [x.diff().diff(), z + sin(z.diff())]])
+    # Test finding all dynamicsymbols
+    sol = {x, y.diff(), y, x.diff().diff(), z, z.diff()}
+    assert find_dynamicsymbols(expr) == sol
+    # Test finding all but those in sym_list
+    exclude_list = [x, y, z]
+    sol = {y.diff(), x.diff().diff(), z.diff()}
+    assert find_dynamicsymbols(expr, exclude=exclude_list) == sol
+    # Test finding all dynamicsymbols in a vector with a given reference frame
+    d, e, f = dynamicsymbols('d, e, f')
+    A = ReferenceFrame('A')
+    v = d * A.x + e * A.y + f * A.z
+    sol = {d, e, f}
+    assert find_dynamicsymbols(v, reference_frame=A) == sol
+    # Test if a ValueError is raised on supplying only a vector as input
+    raises(ValueError, lambda: find_dynamicsymbols(v))
+
+
+def test_gravity():
+    N = ReferenceFrame('N')
+    m, M, g = symbols('m M g')
+    F1, F2 = dynamicsymbols('F1 F2')
+    po = Point('po')
+    pa = Particle('pa', po, m)
+    A = ReferenceFrame('A')
+    P = Point('P')
+    I = outer(A.x, A.x)
+    B = RigidBody('B', P, A, M, (I, P))
+    forceList = [(po, F1), (P, F2)]
+    forceList.extend(gravity(g*N.y, pa, B))
+    l = [(po, F1), (P, F2), (po, g*m*N.y), (P, g*M*N.y)]
+
+    for i in range(len(l)):
+        for j in range(len(l[i])):
+            assert forceList[i][j] == l[i][j]
+
+# This function tests the center_of_mass() function
+# that was added in PR #14758 to compute the center of
+# mass of a system of bodies.
+def test_center_of_mass():
+    a = ReferenceFrame('a')
+    m = symbols('m', real=True)
+    p1 = Particle('p1', Point('p1_pt'), S.One)
+    p2 = Particle('p2', Point('p2_pt'), S(2))
+    p3 = Particle('p3', Point('p3_pt'), S(3))
+    p4 = Particle('p4', Point('p4_pt'), m)
+    b_f = ReferenceFrame('b_f')
+    b_cm = Point('b_cm')
+    mb = symbols('mb')
+    b = RigidBody('b', b_cm, b_f, mb, (outer(b_f.x, b_f.x), b_cm))
+    p2.point.set_pos(p1.point, a.x)
+    p3.point.set_pos(p1.point, a.x + a.y)
+    p4.point.set_pos(p1.point, a.y)
+    b.masscenter.set_pos(p1.point, a.y + a.z)
+    point_o=Point('o')
+    point_o.set_pos(p1.point, center_of_mass(p1.point, p1, p2, p3, p4, b))
+    expr = 5/(m + mb + 6)*a.x + (m + mb + 3)/(m + mb + 6)*a.y + mb/(m + mb + 6)*a.z
+    assert point_o.pos_from(p1.point)-expr == 0
+
+
+def test_validate_coordinates():
+    q1, q2, q3, u1, u2, u3 = dynamicsymbols('q1:4 u1:4')
+    s1, s2, s3 = symbols('s1:4')
+    # Test normal
+    _validate_coordinates([q1, q2, q3], [u1, u2, u3])
+    # Test not equal number of coordinates and speeds
+    _validate_coordinates([q1, q2])
+    _validate_coordinates([q1, q2], [u1])
+    _validate_coordinates(speeds=[u1, u2])
+    # Test duplicate
+    _validate_coordinates([q1, q2, q2], [u1, u2, u3], check_duplicates=False)
+    raises(ValueError, lambda: _validate_coordinates(
+        [q1, q2, q2], [u1, u2, u3]))
+    _validate_coordinates([q1, q2, q3], [u1, u2, u2], check_duplicates=False)
+    raises(ValueError, lambda: _validate_coordinates(
+        [q1, q2, q3], [u1, u2, u2], check_duplicates=True))
+    raises(ValueError, lambda: _validate_coordinates(
+        [q1, q2, q3], [q1, u2, u3], check_duplicates=True))
+    # Test is_dynamicsymbols
+    _validate_coordinates([q1 + q2, q3], is_dynamicsymbols=False)
+    raises(ValueError, lambda: _validate_coordinates([q1 + q2, q3]))
+    _validate_coordinates([s1, q1, q2], [0, u1, u2], is_dynamicsymbols=False)
+    raises(ValueError, lambda: _validate_coordinates(
+        [s1, q1, q2], [0, u1, u2], is_dynamicsymbols=True))
+    _validate_coordinates([s1 + s2 + s3, q1], [0, u1], is_dynamicsymbols=False)
+    raises(ValueError, lambda: _validate_coordinates(
+        [s1 + s2 + s3, q1], [0, u1], is_dynamicsymbols=True))
+    # Test normal function
+    t = dynamicsymbols._t
+    a = symbols('a')
+    f1, f2 = symbols('f1:3', cls=Function)
+    _validate_coordinates([f1(a), f2(a)], is_dynamicsymbols=False)
+    raises(ValueError, lambda: _validate_coordinates([f1(a), f2(a)]))
+    raises(ValueError, lambda: _validate_coordinates(speeds=[f1(a), f2(a)]))
+    dynamicsymbols._t = a
+    _validate_coordinates([f1(a), f2(a)])
+    raises(ValueError, lambda: _validate_coordinates([f1(t), f2(t)]))
+    dynamicsymbols._t = t

venv/lib/python3.10/site-packages/sympy/physics/mechanics/tests/test_joint.py

@@ -0,0 +1,1144 @@
+from sympy.core.function import expand_mul
+from sympy.core.numbers import pi
+from sympy.core.singleton import S
+from sympy.functions.elementary.miscellaneous import sqrt
+from sympy.functions.elementary.trigonometric import (cos, sin)
+from sympy.core.backend import Matrix, _simplify_matrix, eye, zeros
+from sympy.core.symbol import symbols
+from sympy.physics.mechanics import (dynamicsymbols, Body, JointsMethod,
+                                     PinJoint, PrismaticJoint, CylindricalJoint,
+                                     PlanarJoint, SphericalJoint, WeldJoint)
+from sympy.physics.mechanics.joint import Joint
+from sympy.physics.vector import Vector, ReferenceFrame, Point
+from sympy.testing.pytest import raises, warns_deprecated_sympy
+
+
+Vector.simp = True
+t = dynamicsymbols._t # type: ignore
+
+
+def _generate_body(interframe=False):
+    N = ReferenceFrame('N')
+    A = ReferenceFrame('A')
+    P = Body('P', frame=N)
+    C = Body('C', frame=A)
+    if interframe:
+        Pint, Cint = ReferenceFrame('P_int'), ReferenceFrame('C_int')
+        Pint.orient_axis(N, N.x, pi)
+        Cint.orient_axis(A, A.y, -pi / 2)
+        return N, A, P, C, Pint, Cint
+    return N, A, P, C
+
+
+def test_Joint():
+    parent = Body('parent')
+    child = Body('child')
+    raises(TypeError, lambda: Joint('J', parent, child))
+
+
+def test_coordinate_generation():
+    q, u, qj, uj = dynamicsymbols('q u q_J u_J')
+    q0j, q1j, q2j, q3j, u0j, u1j, u2j, u3j = dynamicsymbols('q0:4_J u0:4_J')
+    q0, q1, q2, q3, u0, u1, u2, u3 = dynamicsymbols('q0:4 u0:4')
+    _, _, P, C = _generate_body()
+    # Using PinJoint to access Joint's coordinate generation method
+    J = PinJoint('J', P, C)
+    # Test single given
+    assert J._fill_coordinate_list(q, 1) == Matrix([q])
+    assert J._fill_coordinate_list([u], 1) == Matrix([u])
+    assert J._fill_coordinate_list([u], 1, offset=2) == Matrix([u])
+    # Test None
+    assert J._fill_coordinate_list(None, 1) == Matrix([qj])
+    assert J._fill_coordinate_list([None], 1) == Matrix([qj])
+    assert J._fill_coordinate_list([q0, None, None], 3) == Matrix(
+        [q0, q1j, q2j])
+    # Test autofill
+    assert J._fill_coordinate_list(None, 3) == Matrix([q0j, q1j, q2j])
+    assert J._fill_coordinate_list([], 3) == Matrix([q0j, q1j, q2j])
+    # Test offset
+    assert J._fill_coordinate_list([], 3, offset=1) == Matrix([q1j, q2j, q3j])
+    assert J._fill_coordinate_list([q1, None, q3], 3, offset=1) == Matrix(
+        [q1, q2j, q3])
+    assert J._fill_coordinate_list(None, 2, offset=2) == Matrix([q2j, q3j])
+    # Test label
+    assert J._fill_coordinate_list(None, 1, 'u') == Matrix([uj])
+    assert J._fill_coordinate_list([], 3, 'u') == Matrix([u0j, u1j, u2j])
+    # Test single numbering
+    assert J._fill_coordinate_list(None, 1, number_single=True) == Matrix([q0j])
+    assert J._fill_coordinate_list([], 1, 'u', 2, True) == Matrix([u2j])
+    assert J._fill_coordinate_list([], 3, 'q') == Matrix([q0j, q1j, q2j])
+    # Test invalid number of coordinates supplied
+    raises(ValueError, lambda: J._fill_coordinate_list([q0, q1], 1))
+    raises(ValueError, lambda: J._fill_coordinate_list([u0, u1, None], 2, 'u'))
+    raises(ValueError, lambda: J._fill_coordinate_list([q0, q1], 3))
+    # Test incorrect coordinate type
+    raises(TypeError, lambda: J._fill_coordinate_list([q0, symbols('q1')], 2))
+    raises(TypeError, lambda: J._fill_coordinate_list([q0 + q1, q1], 2))
+    # Test if derivative as generalized speed is allowed
+    _, _, P, C = _generate_body()
+    PinJoint('J', P, C, q1, q1.diff(t))
+    # Test duplicate coordinates
+    _, _, P, C = _generate_body()
+    raises(ValueError, lambda: SphericalJoint('J', P, C, [q1j, None, None]))
+    raises(ValueError, lambda: SphericalJoint('J', P, C, speeds=[u0, u0, u1]))
+
+
+def test_pin_joint():
+    P = Body('P')
+    C = Body('C')
+    l, m = symbols('l m')
+    q, u = dynamicsymbols('q_J, u_J')
+    Pj = PinJoint('J', P, C)
+    assert Pj.name == 'J'
+    assert Pj.parent == P
+    assert Pj.child == C
+    assert Pj.coordinates == Matrix([q])
+    assert Pj.speeds == Matrix([u])
+    assert Pj.kdes == Matrix([u - q.diff(t)])
+    assert Pj.joint_axis == P.frame.x
+    assert Pj.child_point.pos_from(C.masscenter) == Vector(0)
+    assert Pj.parent_point.pos_from(P.masscenter) == Vector(0)
+    assert Pj.parent_point.pos_from(Pj._child_point) == Vector(0)
+    assert C.masscenter.pos_from(P.masscenter) == Vector(0)
+    assert Pj.parent_interframe == P.frame
+    assert Pj.child_interframe == C.frame
+    assert Pj.__str__() == 'PinJoint: J  parent: P  child: C'
+
+    P1 = Body('P1')
+    C1 = Body('C1')
+    Pint = ReferenceFrame('P_int')
+    Pint.orient_axis(P1.frame, P1.y, pi / 2)
+    J1 = PinJoint('J1', P1, C1, parent_point=l*P1.frame.x,
+                  child_point=m*C1.frame.y, joint_axis=P1.frame.z,
+                  parent_interframe=Pint)
+    assert J1._joint_axis == P1.frame.z
+    assert J1._child_point.pos_from(C1.masscenter) == m * C1.frame.y
+    assert J1._parent_point.pos_from(P1.masscenter) == l * P1.frame.x
+    assert J1._parent_point.pos_from(J1._child_point) == Vector(0)
+    assert (P1.masscenter.pos_from(C1.masscenter) ==
+            -l*P1.frame.x + m*C1.frame.y)
+    assert J1.parent_interframe == Pint
+    assert J1.child_interframe == C1.frame
+
+    q, u = dynamicsymbols('q, u')
+    N, A, P, C, Pint, Cint = _generate_body(True)
+    parent_point = P.masscenter.locatenew('parent_point', N.x + N.y)
+    child_point = C.masscenter.locatenew('child_point', C.y + C.z)
+    J = PinJoint('J', P, C, q, u, parent_point=parent_point,
+                 child_point=child_point, parent_interframe=Pint,
+                 child_interframe=Cint, joint_axis=N.z)
+    assert J.joint_axis == N.z
+    assert J.parent_point.vel(N) == 0
+    assert J.parent_point == parent_point
+    assert J.child_point == child_point
+    assert J.child_point.pos_from(P.masscenter) == N.x + N.y
+    assert J.parent_point.pos_from(C.masscenter) == C.y + C.z
+    assert C.masscenter.pos_from(P.masscenter) == N.x + N.y - C.y - C.z
+    assert C.masscenter.vel(N).express(N) == (u * sin(q) - u * cos(q)) * N.x + (
+            -u * sin(q) - u * cos(q)) * N.y
+    assert J.parent_interframe == Pint
+    assert J.child_interframe == Cint
+
+
+def test_pin_joint_double_pendulum():
+    q1, q2 = dynamicsymbols('q1 q2')
+    u1, u2 = dynamicsymbols('u1 u2')
+    m, l = symbols('m l')
+    N = ReferenceFrame('N')
+    A = ReferenceFrame('A')
+    B = ReferenceFrame('B')
+    C = Body('C', frame=N)  # ceiling
+    PartP = Body('P', frame=A, mass=m)
+    PartR = Body('R', frame=B, mass=m)
+
+    J1 = PinJoint('J1', C, PartP, speeds=u1, coordinates=q1,
+                  child_point=-l*A.x, joint_axis=C.frame.z)
+    J2 = PinJoint('J2', PartP, PartR, speeds=u2, coordinates=q2,
+                  child_point=-l*B.x, joint_axis=PartP.frame.z)
+
+    # Check orientation
+    assert N.dcm(A) == Matrix([[cos(q1), -sin(q1), 0],
+                               [sin(q1), cos(q1), 0], [0, 0, 1]])
+    assert A.dcm(B) == Matrix([[cos(q2), -sin(q2), 0],
+                               [sin(q2), cos(q2), 0], [0, 0, 1]])
+    assert _simplify_matrix(N.dcm(B)) == Matrix([[cos(q1 + q2), -sin(q1 + q2), 0],
+                                                 [sin(q1 + q2), cos(q1 + q2), 0],
+                                                 [0, 0, 1]])
+
+    # Check Angular Velocity
+    assert A.ang_vel_in(N) == u1 * N.z
+    assert B.ang_vel_in(A) == u2 * A.z
+    assert B.ang_vel_in(N) == u1 * N.z + u2 * A.z
+
+    # Check kde
+    assert J1.kdes == Matrix([u1 - q1.diff(t)])
+    assert J2.kdes == Matrix([u2 - q2.diff(t)])
+
+    # Check Linear Velocity
+    assert PartP.masscenter.vel(N) == l*u1*A.y
+    assert PartR.masscenter.vel(A) == l*u2*B.y
+    assert PartR.masscenter.vel(N) == l*u1*A.y + l*(u1 + u2)*B.y
+
+
+def test_pin_joint_chaos_pendulum():
+    mA, mB, lA, lB, h = symbols('mA, mB, lA, lB, h')
+    theta, phi, omega, alpha = dynamicsymbols('theta phi omega alpha')
+    N = ReferenceFrame('N')
+    A = ReferenceFrame('A')
+    B = ReferenceFrame('B')
+    lA = (lB - h / 2) / 2
+    lC = (lB/2 + h/4)
+    rod = Body('rod', frame=A, mass=mA)
+    plate = Body('plate', mass=mB, frame=B)
+    C = Body('C', frame=N)
+    J1 = PinJoint('J1', C, rod, coordinates=theta, speeds=omega,
+                  child_point=lA*A.z, joint_axis=N.y)
+    J2 = PinJoint('J2', rod, plate, coordinates=phi, speeds=alpha,
+                  parent_point=lC*A.z, joint_axis=A.z)
+
+    # Check orientation
+    assert A.dcm(N) == Matrix([[cos(theta), 0, -sin(theta)],
+                               [0, 1, 0],
+                               [sin(theta), 0, cos(theta)]])
+    assert A.dcm(B) == Matrix([[cos(phi), -sin(phi), 0],
+                               [sin(phi), cos(phi), 0],
+                               [0, 0, 1]])
+    assert B.dcm(N) == Matrix([
+        [cos(phi)*cos(theta), sin(phi), -sin(theta)*cos(phi)],
+        [-sin(phi)*cos(theta), cos(phi), sin(phi)*sin(theta)],
+        [sin(theta), 0, cos(theta)]])
+
+    # Check Angular Velocity
+    assert A.ang_vel_in(N) == omega*N.y
+    assert A.ang_vel_in(B) == -alpha*A.z
+    assert N.ang_vel_in(B) == -omega*N.y - alpha*A.z
+
+    # Check kde
+    assert J1.kdes == Matrix([omega - theta.diff(t)])
+    assert J2.kdes == Matrix([alpha - phi.diff(t)])
+
+    # Check pos of masscenters
+    assert C.masscenter.pos_from(rod.masscenter) == lA*A.z
+    assert rod.masscenter.pos_from(plate.masscenter) == - lC * A.z
+
+    # Check Linear Velocities
+    assert rod.masscenter.vel(N) == (h/4 - lB/2)*omega*A.x
+    assert plate.masscenter.vel(N) == ((h/4 - lB/2)*omega +
+                                       (h/4 + lB/2)*omega)*A.x
+
+
+def test_pin_joint_interframe():
+    q, u = dynamicsymbols('q, u')
+    # Check not connected
+    N, A, P, C = _generate_body()
+    Pint, Cint = ReferenceFrame('Pint'), ReferenceFrame('Cint')
+    raises(ValueError, lambda: PinJoint('J', P, C, parent_interframe=Pint))
+    raises(ValueError, lambda: PinJoint('J', P, C, child_interframe=Cint))
+    # Check not fixed interframe
+    Pint.orient_axis(N, N.z, q)
+    Cint.orient_axis(A, A.z, q)
+    raises(ValueError, lambda: PinJoint('J', P, C, parent_interframe=Pint))
+    raises(ValueError, lambda: PinJoint('J', P, C, child_interframe=Cint))
+    # Check only parent_interframe
+    N, A, P, C = _generate_body()
+    Pint = ReferenceFrame('Pint')
+    Pint.orient_body_fixed(N, (pi / 4, pi, pi / 3), 'xyz')
+    PinJoint('J', P, C, q, u, parent_point=N.x, child_point=-C.y,
+             parent_interframe=Pint, joint_axis=Pint.x)
+    assert _simplify_matrix(N.dcm(A)) - Matrix([
+        [-1 / 2, sqrt(3) * cos(q) / 2, -sqrt(3) * sin(q) / 2],
+        [sqrt(6) / 4, sqrt(2) * (2 * sin(q) + cos(q)) / 4,
+         sqrt(2) * (-sin(q) + 2 * cos(q)) / 4],
+        [sqrt(6) / 4, sqrt(2) * (-2 * sin(q) + cos(q)) / 4,
+         -sqrt(2) * (sin(q) + 2 * cos(q)) / 4]]) == zeros(3)
+    assert A.ang_vel_in(N) == u * Pint.x
+    assert C.masscenter.pos_from(P.masscenter) == N.x + A.y
+    assert C.masscenter.vel(N) == u * A.z
+    assert P.masscenter.vel(Pint) == Vector(0)
+    assert C.masscenter.vel(Pint) == u * A.z
+    # Check only child_interframe
+    N, A, P, C = _generate_body()
+    Cint = ReferenceFrame('Cint')
+    Cint.orient_body_fixed(A, (2 * pi / 3, -pi, pi / 2), 'xyz')
+    PinJoint('J', P, C, q, u, parent_point=-N.z, child_point=C.x,
+             child_interframe=Cint, joint_axis=P.x + P.z)
+    assert _simplify_matrix(N.dcm(A)) == Matrix([
+        [-sqrt(2) * sin(q) / 2,
+         -sqrt(3) * (cos(q) - 1) / 4 - cos(q) / 4 - S(1) / 4,
+         sqrt(3) * (cos(q) + 1) / 4 - cos(q) / 4 + S(1) / 4],
+        [cos(q), (sqrt(2) + sqrt(6)) * -sin(q) / 4,
+         (-sqrt(2) + sqrt(6)) * sin(q) / 4],
+        [sqrt(2) * sin(q) / 2,
+         sqrt(3) * (cos(q) + 1) / 4 + cos(q) / 4 - S(1) / 4,
+         sqrt(3) * (1 - cos(q)) / 4 + cos(q) / 4 + S(1) / 4]])
+    assert A.ang_vel_in(N) == sqrt(2) * u / 2 * N.x + sqrt(2) * u / 2 * N.z
+    assert C.masscenter.pos_from(P.masscenter) == - N.z - A.x
+    assert C.masscenter.vel(N).simplify() == (
+        -sqrt(6) - sqrt(2)) * u / 4 * A.y + (
+               -sqrt(2) + sqrt(6)) * u / 4 * A.z
+    assert C.masscenter.vel(Cint) == Vector(0)
+    # Check combination
+    N, A, P, C = _generate_body()
+    Pint, Cint = ReferenceFrame('Pint'), ReferenceFrame('Cint')
+    Pint.orient_body_fixed(N, (-pi / 2, pi, pi / 2), 'xyz')
+    Cint.orient_body_fixed(A, (2 * pi / 3, -pi, pi / 2), 'xyz')
+    PinJoint('J', P, C, q, u, parent_point=N.x - N.y, child_point=-C.z,
+             parent_interframe=Pint, child_interframe=Cint,
+             joint_axis=Pint.x + Pint.z)
+    assert _simplify_matrix(N.dcm(A)) == Matrix([
+        [cos(q), (sqrt(2) + sqrt(6)) * -sin(q) / 4,
+         (-sqrt(2) + sqrt(6)) * sin(q) / 4],
+        [-sqrt(2) * sin(q) / 2,
+         -sqrt(3) * (cos(q) + 1) / 4 - cos(q) / 4 + S(1) / 4,
+         sqrt(3) * (cos(q) - 1) / 4 - cos(q) / 4 - S(1) / 4],
+        [sqrt(2) * sin(q) / 2,
+         sqrt(3) * (cos(q) - 1) / 4 + cos(q) / 4 + S(1) / 4,
+         -sqrt(3) * (cos(q) + 1) / 4 + cos(q) / 4 - S(1) / 4]])
+    assert A.ang_vel_in(N) == sqrt(2) * u / 2 * Pint.x + sqrt(
+        2) * u / 2 * Pint.z
+    assert C.masscenter.pos_from(P.masscenter) == N.x - N.y + A.z
+    N_v_C = (-sqrt(2) + sqrt(6)) * u / 4 * A.x
+    assert C.masscenter.vel(N).simplify() == N_v_C
+    assert C.masscenter.vel(Pint).simplify() == N_v_C
+    assert C.masscenter.vel(Cint) == Vector(0)
+
+
+def test_pin_joint_joint_axis():
+    q, u = dynamicsymbols('q, u')
+    # Check parent as reference
+    N, A, P, C, Pint, Cint = _generate_body(True)
+    pin = PinJoint('J', P, C, q, u, parent_interframe=Pint,
+                   child_interframe=Cint, joint_axis=P.y)
+    assert pin.joint_axis == P.y
+    assert N.dcm(A) == Matrix([[sin(q), 0, cos(q)], [0, -1, 0],
+                               [cos(q), 0, -sin(q)]])
+    # Check parent_interframe as reference
+    N, A, P, C, Pint, Cint = _generate_body(True)
+    pin = PinJoint('J', P, C, q, u, parent_interframe=Pint,
+                   child_interframe=Cint, joint_axis=Pint.y)
+    assert pin.joint_axis == Pint.y
+    assert N.dcm(A) == Matrix([[-sin(q), 0, cos(q)], [0, -1, 0],
+                               [cos(q), 0, sin(q)]])
+    # Check combination of joint_axis with interframes supplied as vectors (2x)
+    N, A, P, C = _generate_body()
+    pin = PinJoint('J', P, C, q, u, parent_interframe=N.z,
+                   child_interframe=-C.z, joint_axis=N.z)
+    assert pin.joint_axis == N.z
+    assert N.dcm(A) == Matrix([[-cos(q), -sin(q), 0], [-sin(q), cos(q), 0],
+                               [0, 0, -1]])
+    N, A, P, C = _generate_body()
+    pin = PinJoint('J', P, C, q, u, parent_interframe=N.z,
+                   child_interframe=-C.z, joint_axis=N.x)
+    assert pin.joint_axis == N.x
+    assert N.dcm(A) == Matrix([[-1, 0, 0], [0, cos(q), sin(q)],
+                               [0, sin(q), -cos(q)]])
+    # Check time varying axis
+    N, A, P, C, Pint, Cint = _generate_body(True)
+    raises(ValueError, lambda: PinJoint('J', P, C,
+                                        joint_axis=cos(q) * N.x + sin(q) * N.y))
+    # Check joint_axis provided in child frame
+    raises(ValueError, lambda: PinJoint('J', P, C, joint_axis=C.x))
+    # Check some invalid combinations
+    raises(ValueError, lambda: PinJoint('J', P, C, joint_axis=P.x + C.y))
+    raises(ValueError, lambda: PinJoint(
+        'J', P, C, parent_interframe=Pint, child_interframe=Cint,
+        joint_axis=Pint.x + C.y))
+    raises(ValueError, lambda: PinJoint(
+        'J', P, C, parent_interframe=Pint, child_interframe=Cint,
+        joint_axis=P.x + Cint.y))
+    # Check valid special combination
+    N, A, P, C, Pint, Cint = _generate_body(True)
+    PinJoint('J', P, C, parent_interframe=Pint, child_interframe=Cint,
+             joint_axis=Pint.x + P.y)
+    # Check invalid zero vector
+    raises(Exception, lambda: PinJoint(
+        'J', P, C, parent_interframe=Pint, child_interframe=Cint,
+        joint_axis=Vector(0)))
+    raises(Exception, lambda: PinJoint(
+        'J', P, C, parent_interframe=Pint, child_interframe=Cint,
+        joint_axis=P.y + Pint.y))
+
+
+def test_pin_joint_arbitrary_axis():
+    q, u = dynamicsymbols('q_J, u_J')
+
+    # When the bodies are attached though masscenters but axes are opposite.
+    N, A, P, C = _generate_body()
+    PinJoint('J', P, C, child_interframe=-A.x)
+
+    assert (-A.x).angle_between(N.x) == 0
+    assert -A.x.express(N) == N.x
+    assert A.dcm(N) == Matrix([[-1, 0, 0],
+                               [0, -cos(q), -sin(q)],
+                               [0, -sin(q), cos(q)]])
+    assert A.ang_vel_in(N) == u*N.x
+    assert A.ang_vel_in(N).magnitude() == sqrt(u**2)
+    assert C.masscenter.pos_from(P.masscenter) == 0
+    assert C.masscenter.pos_from(P.masscenter).express(N).simplify() == 0
+    assert C.masscenter.vel(N) == 0
+
+    # When axes are different and parent joint is at masscenter but child joint
+    # is at a unit vector from child masscenter.
+    N, A, P, C = _generate_body()
+    PinJoint('J', P, C, child_interframe=A.y, child_point=A.x)
+
+    assert A.y.angle_between(N.x) == 0  # Axis are aligned
+    assert A.y.express(N) == N.x
+    assert A.dcm(N) == Matrix([[0, -cos(q), -sin(q)],
+                               [1, 0, 0],
+                               [0, -sin(q), cos(q)]])
+    assert A.ang_vel_in(N) == u*N.x
+    assert A.ang_vel_in(N).express(A) == u * A.y
+    assert A.ang_vel_in(N).magnitude() == sqrt(u**2)
+    assert A.ang_vel_in(N).cross(A.y) == 0
+    assert C.masscenter.vel(N) == u*A.z
+    assert C.masscenter.pos_from(P.masscenter) == -A.x
+    assert (C.masscenter.pos_from(P.masscenter).express(N).simplify() ==
+            cos(q)*N.y + sin(q)*N.z)
+    assert C.masscenter.vel(N).angle_between(A.x) == pi/2
+
+    # Similar to previous case but wrt parent body
+    N, A, P, C = _generate_body()
+    PinJoint('J', P, C, parent_interframe=N.y, parent_point=N.x)
+
+    assert N.y.angle_between(A.x) == 0  # Axis are aligned
+    assert N.y.express(A) == A.x
+    assert A.dcm(N) == Matrix([[0, 1, 0],
+                               [-cos(q), 0, sin(q)],
+                               [sin(q), 0, cos(q)]])
+    assert A.ang_vel_in(N) == u*N.y
+    assert A.ang_vel_in(N).express(A) == u*A.x
+    assert A.ang_vel_in(N).magnitude() == sqrt(u**2)
+    angle = A.ang_vel_in(N).angle_between(A.x)
+    assert angle.xreplace({u: 1}) == 0
+    assert C.masscenter.vel(N) == 0
+    assert C.masscenter.pos_from(P.masscenter) == N.x
+
+    # Both joint pos id defined but different axes
+    N, A, P, C = _generate_body()
+    PinJoint('J', P, C, parent_point=N.x, child_point=A.x,
+             child_interframe=A.x + A.y)
+    assert expand_mul(N.x.angle_between(A.x + A.y)) == 0  # Axis are aligned
+    assert (A.x + A.y).express(N).simplify() == sqrt(2)*N.x
+    assert _simplify_matrix(A.dcm(N)) == Matrix([
+        [sqrt(2)/2, -sqrt(2)*cos(q)/2, -sqrt(2)*sin(q)/2],
+        [sqrt(2)/2, sqrt(2)*cos(q)/2, sqrt(2)*sin(q)/2],
+        [0, -sin(q), cos(q)]])
+    assert A.ang_vel_in(N) == u*N.x
+    assert (A.ang_vel_in(N).express(A).simplify() ==
+            (u*A.x + u*A.y)/sqrt(2))
+    assert A.ang_vel_in(N).magnitude() == sqrt(u**2)
+    angle = A.ang_vel_in(N).angle_between(A.x + A.y)
+    assert angle.xreplace({u: 1}) == 0
+    assert C.masscenter.vel(N).simplify() == (u * A.z)/sqrt(2)
+    assert C.masscenter.pos_from(P.masscenter) == N.x - A.x
+    assert (C.masscenter.pos_from(P.masscenter).express(N).simplify() ==
+            (1 - sqrt(2)/2)*N.x + sqrt(2)*cos(q)/2*N.y +
+            sqrt(2)*sin(q)/2*N.z)
+    assert (C.masscenter.vel(N).express(N).simplify() ==
+            -sqrt(2)*u*sin(q)/2*N.y + sqrt(2)*u*cos(q)/2*N.z)
+    assert C.masscenter.vel(N).angle_between(A.x) == pi/2
+
+    N, A, P, C = _generate_body()
+    PinJoint('J', P, C, parent_point=N.x, child_point=A.x,
+             child_interframe=A.x + A.y - A.z)
+    assert expand_mul(N.x.angle_between(A.x + A.y - A.z)) == 0  # Axis aligned
+    assert (A.x + A.y - A.z).express(N).simplify() == sqrt(3)*N.x
+    assert _simplify_matrix(A.dcm(N)) == Matrix([
+        [sqrt(3)/3, -sqrt(6)*sin(q + pi/4)/3,
+         sqrt(6)*cos(q + pi/4)/3],
+        [sqrt(3)/3, sqrt(6)*cos(q + pi/12)/3,
+         sqrt(6)*sin(q + pi/12)/3],
+        [-sqrt(3)/3, sqrt(6)*cos(q + 5*pi/12)/3,
+         sqrt(6)*sin(q + 5*pi/12)/3]])
+    assert A.ang_vel_in(N) == u*N.x
+    assert A.ang_vel_in(N).express(A).simplify() == (u*A.x + u*A.y -
+                                                     u*A.z)/sqrt(3)
+    assert A.ang_vel_in(N).magnitude() == sqrt(u**2)
+    angle = A.ang_vel_in(N).angle_between(A.x + A.y-A.z)
+    assert angle.xreplace({u: 1}) == 0
+    assert C.masscenter.vel(N).simplify() == (u*A.y + u*A.z)/sqrt(3)
+    assert C.masscenter.pos_from(P.masscenter) == N.x - A.x
+    assert (C.masscenter.pos_from(P.masscenter).express(N).simplify() ==
+            (1 - sqrt(3)/3)*N.x + sqrt(6)*sin(q + pi/4)/3*N.y -
+            sqrt(6)*cos(q + pi/4)/3*N.z)
+    assert (C.masscenter.vel(N).express(N).simplify() ==
+            sqrt(6)*u*cos(q + pi/4)/3*N.y +
+            sqrt(6)*u*sin(q + pi/4)/3*N.z)
+    assert C.masscenter.vel(N).angle_between(A.x) == pi/2
+
+    N, A, P, C = _generate_body()
+    m, n = symbols('m n')
+    PinJoint('J', P, C, parent_point=m * N.x, child_point=n * A.x,
+             child_interframe=A.x + A.y - A.z,
+             parent_interframe=N.x - N.y + N.z)
+    angle = (N.x - N.y + N.z).angle_between(A.x + A.y - A.z)
+    assert expand_mul(angle) == 0  # Axis are aligned
+    assert ((A.x-A.y+A.z).express(N).simplify() ==
+            (-4*cos(q)/3 - S(1)/3)*N.x + (S(1)/3 - 4*sin(q + pi/6)/3)*N.y +
+            (4*cos(q + pi/3)/3 - S(1)/3)*N.z)
+    assert _simplify_matrix(A.dcm(N)) == Matrix([
+        [S(1)/3 - 2*cos(q)/3, -2*sin(q + pi/6)/3 - S(1)/3,
+         2*cos(q + pi/3)/3 + S(1)/3],
+        [2*cos(q + pi/3)/3 + S(1)/3, 2*cos(q)/3 - S(1)/3,
+         2*sin(q + pi/6)/3 + S(1)/3],
+        [-2*sin(q + pi/6)/3 - S(1)/3, 2*cos(q + pi/3)/3 + S(1)/3,
+         2*cos(q)/3 - S(1)/3]])
+    assert A.ang_vel_in(N) == (u*N.x - u*N.y + u*N.z)/sqrt(3)
+    assert A.ang_vel_in(N).express(A).simplify() == (u*A.x + u*A.y -
+                                                     u*A.z)/sqrt(3)
+    assert A.ang_vel_in(N).magnitude() == sqrt(u**2)
+    angle = A.ang_vel_in(N).angle_between(A.x+A.y-A.z)
+    assert angle.xreplace({u: 1}) == 0
+    assert (C.masscenter.vel(N).simplify() ==
+            sqrt(3)*n*u/3*A.y + sqrt(3)*n*u/3*A.z)
+    assert C.masscenter.pos_from(P.masscenter) == m*N.x - n*A.x
+    assert (C.masscenter.pos_from(P.masscenter).express(N).simplify() ==
+            (m + n*(2*cos(q) - 1)/3)*N.x + n*(2*sin(q + pi/6) +
+            1)/3*N.y - n*(2*cos(q + pi/3) + 1)/3*N.z)
+    assert (C.masscenter.vel(N).express(N).simplify() ==
+            - 2*n*u*sin(q)/3*N.x + 2*n*u*cos(q + pi/6)/3*N.y +
+            2*n*u*sin(q + pi/3)/3*N.z)
+    assert C.masscenter.vel(N).dot(N.x - N.y + N.z).simplify() == 0
+
+
+def test_create_aligned_frame_pi():
+    N, A, P, C = _generate_body()
+    f = Joint._create_aligned_interframe(P, -P.x, P.x)
+    assert f.z == P.z
+    f = Joint._create_aligned_interframe(P, -P.y, P.y)
+    assert f.x == P.x
+    f = Joint._create_aligned_interframe(P, -P.z, P.z)
+    assert f.y == P.y
+    f = Joint._create_aligned_interframe(P, -P.x - P.y, P.x + P.y)
+    assert f.z == P.z
+    f = Joint._create_aligned_interframe(P, -P.y - P.z, P.y + P.z)
+    assert f.x == P.x
+    f = Joint._create_aligned_interframe(P, -P.x - P.z, P.x + P.z)
+    assert f.y == P.y
+    f = Joint._create_aligned_interframe(P, -P.x - P.y - P.z, P.x + P.y + P.z)
+    assert f.y - f.z == P.y - P.z
+
+
+def test_pin_joint_axis():
+    q, u = dynamicsymbols('q u')
+    # Test default joint axis
+    N, A, P, C, Pint, Cint = _generate_body(True)
+    J = PinJoint('J', P, C, q, u, parent_interframe=Pint, child_interframe=Cint)
+    assert J.joint_axis == Pint.x
+    # Test for the same joint axis expressed in different frames
+    N_R_A = Matrix([[0, sin(q), cos(q)],
+                    [0, -cos(q), sin(q)],
+                    [1, 0, 0]])
+    N, A, P, C, Pint, Cint = _generate_body(True)
+    PinJoint('J', P, C, q, u, parent_interframe=Pint, child_interframe=Cint,
+             joint_axis=N.z)
+    assert N.dcm(A) == N_R_A
+    N, A, P, C, Pint, Cint = _generate_body(True)
+    PinJoint('J', P, C, q, u, parent_interframe=Pint, child_interframe=Cint,
+             joint_axis=-Pint.z)
+    assert N.dcm(A) == N_R_A
+    # Test time varying joint axis
+    N, A, P, C, Pint, Cint = _generate_body(True)
+    raises(ValueError, lambda: PinJoint('J', P, C, joint_axis=q * N.z))
+
+
+def test_locate_joint_pos():
+    # Test Vector and default
+    N, A, P, C = _generate_body()
+    joint = PinJoint('J', P, C, parent_point=N.y + N.z)
+    assert joint.parent_point.name == 'J_P_joint'
+    assert joint.parent_point.pos_from(P.masscenter) == N.y + N.z
+    assert joint.child_point == C.masscenter
+    # Test Point objects
+    N, A, P, C = _generate_body()
+    parent_point = P.masscenter.locatenew('p', N.y + N.z)
+    joint = PinJoint('J', P, C, parent_point=parent_point,
+                     child_point=C.masscenter)
+    assert joint.parent_point == parent_point
+    assert joint.child_point == C.masscenter
+    # Check invalid type
+    N, A, P, C = _generate_body()
+    raises(TypeError,
+           lambda: PinJoint('J', P, C, parent_point=N.x.to_matrix(N)))
+    # Test time varying positions
+    q = dynamicsymbols('q')
+    N, A, P, C = _generate_body()
+    raises(ValueError, lambda: PinJoint('J', P, C, parent_point=q * N.x))
+    N, A, P, C = _generate_body()
+    child_point = C.masscenter.locatenew('p', q * A.y)
+    raises(ValueError, lambda: PinJoint('J', P, C, child_point=child_point))
+    # Test undefined position
+    child_point = Point('p')
+    raises(ValueError, lambda: PinJoint('J', P, C, child_point=child_point))
+
+
+def test_locate_joint_frame():
+    # Test rotated frame and default
+    N, A, P, C = _generate_body()
+    parent_interframe = ReferenceFrame('int_frame')
+    parent_interframe.orient_axis(N, N.z, 1)
+    joint = PinJoint('J', P, C, parent_interframe=parent_interframe)
+    assert joint.parent_interframe == parent_interframe
+    assert joint.parent_interframe.ang_vel_in(N) == 0
+    assert joint.child_interframe == A
+    # Test time varying orientations
+    q = dynamicsymbols('q')
+    N, A, P, C = _generate_body()
+    parent_interframe = ReferenceFrame('int_frame')
+    parent_interframe.orient_axis(N, N.z, q)
+    raises(ValueError,
+           lambda: PinJoint('J', P, C, parent_interframe=parent_interframe))
+    # Test undefined frame
+    N, A, P, C = _generate_body()
+    child_interframe = ReferenceFrame('int_frame')
+    child_interframe.orient_axis(N, N.z, 1)  # Defined with respect to parent
+    raises(ValueError,
+           lambda: PinJoint('J', P, C, child_interframe=child_interframe))
+
+
+def test_sliding_joint():
+    _, _, P, C = _generate_body()
+    q, u = dynamicsymbols('q_S, u_S')
+    S = PrismaticJoint('S', P, C)
+    assert S.name == 'S'
+    assert S.parent == P
+    assert S.child == C
+    assert S.coordinates == Matrix([q])
+    assert S.speeds == Matrix([u])
+    assert S.kdes == Matrix([u - q.diff(t)])
+    assert S.joint_axis == P.frame.x
+    assert S.child_point.pos_from(C.masscenter) == Vector(0)
+    assert S.parent_point.pos_from(P.masscenter) == Vector(0)
+    assert S.parent_point.pos_from(S.child_point) == - q * P.frame.x
+    assert P.masscenter.pos_from(C.masscenter) == - q * P.frame.x
+    assert C.masscenter.vel(P.frame) == u * P.frame.x
+    assert P.ang_vel_in(C) == 0
+    assert C.ang_vel_in(P) == 0
+    assert S.__str__() == 'PrismaticJoint: S  parent: P  child: C'
+
+    N, A, P, C = _generate_body()
+    l, m = symbols('l m')
+    Pint = ReferenceFrame('P_int')
+    Pint.orient_axis(P.frame, P.y, pi / 2)
+    S = PrismaticJoint('S', P, C, parent_point=l * P.frame.x,
+                       child_point=m * C.frame.y, joint_axis=P.frame.z,
+                       parent_interframe=Pint)
+
+    assert S.joint_axis == P.frame.z
+    assert S.child_point.pos_from(C.masscenter) == m * C.frame.y
+    assert S.parent_point.pos_from(P.masscenter) == l * P.frame.x
+    assert S.parent_point.pos_from(S.child_point) == - q * P.frame.z
+    assert P.masscenter.pos_from(C.masscenter) == - l*N.x - q*N.z + m*A.y
+    assert C.masscenter.vel(P.frame) == u * P.frame.z
+    assert P.masscenter.vel(Pint) == Vector(0)
+    assert C.ang_vel_in(P) == 0
+    assert P.ang_vel_in(C) == 0
+
+    _, _, P, C = _generate_body()
+    Pint = ReferenceFrame('P_int')
+    Pint.orient_axis(P.frame, P.y, pi / 2)
+    S = PrismaticJoint('S', P, C, parent_point=l * P.frame.z,
+                       child_point=m * C.frame.x, joint_axis=P.frame.z,
+                       parent_interframe=Pint)
+    assert S.joint_axis == P.frame.z
+    assert S.child_point.pos_from(C.masscenter) == m * C.frame.x
+    assert S.parent_point.pos_from(P.masscenter) == l * P.frame.z
+    assert S.parent_point.pos_from(S.child_point) == - q * P.frame.z
+    assert P.masscenter.pos_from(C.masscenter) == (-l - q)*P.frame.z + m*C.frame.x
+    assert C.masscenter.vel(P.frame) == u * P.frame.z
+    assert C.ang_vel_in(P) == 0
+    assert P.ang_vel_in(C) == 0
+
+
+def test_sliding_joint_arbitrary_axis():
+    q, u = dynamicsymbols('q_S, u_S')
+
+    N, A, P, C = _generate_body()
+    PrismaticJoint('S', P, C, child_interframe=-A.x)
+
+    assert (-A.x).angle_between(N.x) == 0
+    assert -A.x.express(N) == N.x
+    assert A.dcm(N) == Matrix([[-1, 0, 0], [0, -1, 0], [0, 0, 1]])
+    assert C.masscenter.pos_from(P.masscenter) == q * N.x
+    assert C.masscenter.pos_from(P.masscenter).express(A).simplify() == -q * A.x
+    assert C.masscenter.vel(N) == u * N.x
+    assert C.masscenter.vel(N).express(A) == -u * A.x
+    assert A.ang_vel_in(N) == 0
+    assert N.ang_vel_in(A) == 0
+
+    #When axes are different and parent joint is at masscenter but child joint is at a unit vector from
+    #child masscenter.
+    N, A, P, C = _generate_body()
+    PrismaticJoint('S', P, C, child_interframe=A.y, child_point=A.x)
+
+    assert A.y.angle_between(N.x) == 0 #Axis are aligned
+    assert A.y.express(N) == N.x
+    assert A.dcm(N) == Matrix([[0, -1, 0], [1, 0, 0], [0, 0, 1]])
+    assert C.masscenter.vel(N) == u * N.x
+    assert C.masscenter.vel(N).express(A) == u * A.y
+    assert C.masscenter.pos_from(P.masscenter) == q*N.x - A.x
+    assert C.masscenter.pos_from(P.masscenter).express(N).simplify() == q*N.x + N.y
+    assert A.ang_vel_in(N) == 0
+    assert N.ang_vel_in(A) == 0
+
+    #Similar to previous case but wrt parent body
+    N, A, P, C = _generate_body()
+    PrismaticJoint('S', P, C, parent_interframe=N.y, parent_point=N.x)
+
+    assert N.y.angle_between(A.x) == 0 #Axis are aligned
+    assert N.y.express(A) ==  A.x
+    assert A.dcm(N) == Matrix([[0, 1, 0], [-1, 0, 0], [0, 0, 1]])
+    assert C.masscenter.vel(N) == u * N.y
+    assert C.masscenter.vel(N).express(A) == u * A.x
+    assert C.masscenter.pos_from(P.masscenter) == N.x + q*N.y
+    assert A.ang_vel_in(N) == 0
+    assert N.ang_vel_in(A) == 0
+
+    #Both joint pos is defined but different axes
+    N, A, P, C = _generate_body()
+    PrismaticJoint('S', P, C, parent_point=N.x, child_point=A.x,
+                   child_interframe=A.x + A.y)
+    assert N.x.angle_between(A.x + A.y) == 0 #Axis are aligned
+    assert (A.x + A.y).express(N) == sqrt(2)*N.x
+    assert A.dcm(N) == Matrix([[sqrt(2)/2, -sqrt(2)/2, 0], [sqrt(2)/2, sqrt(2)/2, 0], [0, 0, 1]])
+    assert C.masscenter.pos_from(P.masscenter) == (q + 1)*N.x - A.x
+    assert C.masscenter.pos_from(P.masscenter).express(N) == (q - sqrt(2)/2 + 1)*N.x + sqrt(2)/2*N.y
+    assert C.masscenter.vel(N).express(A) == u * (A.x + A.y)/sqrt(2)
+    assert C.masscenter.vel(N) == u*N.x
+    assert A.ang_vel_in(N) == 0
+    assert N.ang_vel_in(A) == 0
+
+    N, A, P, C = _generate_body()
+    PrismaticJoint('S', P, C, parent_point=N.x, child_point=A.x,
+                   child_interframe=A.x + A.y - A.z)
+    assert N.x.angle_between(A.x + A.y - A.z) == 0 #Axis are aligned
+    assert (A.x + A.y - A.z).express(N) == sqrt(3)*N.x
+    assert _simplify_matrix(A.dcm(N)) == Matrix([[sqrt(3)/3, -sqrt(3)/3, sqrt(3)/3],
+                                                 [sqrt(3)/3, sqrt(3)/6 + S(1)/2, S(1)/2 - sqrt(3)/6],
+                                                 [-sqrt(3)/3, S(1)/2 - sqrt(3)/6, sqrt(3)/6 + S(1)/2]])
+    assert C.masscenter.pos_from(P.masscenter) == (q + 1)*N.x - A.x
+    assert C.masscenter.pos_from(P.masscenter).express(N) == \
+        (q - sqrt(3)/3 + 1)*N.x + sqrt(3)/3*N.y - sqrt(3)/3*N.z
+    assert C.masscenter.vel(N) == u*N.x
+    assert C.masscenter.vel(N).express(A) == sqrt(3)*u/3*A.x + sqrt(3)*u/3*A.y - sqrt(3)*u/3*A.z
+    assert A.ang_vel_in(N) == 0
+    assert N.ang_vel_in(A) == 0
+
+    N, A, P, C = _generate_body()
+    m, n = symbols('m n')
+    PrismaticJoint('S', P, C, parent_point=m*N.x, child_point=n*A.x,
+                   child_interframe=A.x + A.y - A.z,
+                   parent_interframe=N.x - N.y + N.z)
+    # 0 angle means that the axis are aligned
+    assert (N.x-N.y+N.z).angle_between(A.x+A.y-A.z).simplify() == 0
+    assert (A.x+A.y-A.z).express(N) == N.x - N.y + N.z
+    assert _simplify_matrix(A.dcm(N)) == Matrix([[-S(1)/3, -S(2)/3, S(2)/3],
+                                                 [S(2)/3, S(1)/3, S(2)/3],
+                                                 [-S(2)/3, S(2)/3, S(1)/3]])
+    assert C.masscenter.pos_from(P.masscenter) == \
+        (m + sqrt(3)*q/3)*N.x - sqrt(3)*q/3*N.y + sqrt(3)*q/3*N.z - n*A.x
+    assert C.masscenter.pos_from(P.masscenter).express(N) == \
+        (m + n/3 + sqrt(3)*q/3)*N.x + (2*n/3 - sqrt(3)*q/3)*N.y + (-2*n/3 + sqrt(3)*q/3)*N.z
+    assert C.masscenter.vel(N) == sqrt(3)*u/3*N.x - sqrt(3)*u/3*N.y + sqrt(3)*u/3*N.z
+    assert C.masscenter.vel(N).express(A) == sqrt(3)*u/3*A.x + sqrt(3)*u/3*A.y - sqrt(3)*u/3*A.z
+    assert A.ang_vel_in(N) == 0
+    assert N.ang_vel_in(A) == 0
+
+
+def test_cylindrical_joint():
+    N, A, P, C = _generate_body()
+    q0_def, q1_def, u0_def, u1_def = dynamicsymbols('q0:2_J, u0:2_J')
+    Cj = CylindricalJoint('J', P, C)
+    assert Cj.name == 'J'
+    assert Cj.parent == P
+    assert Cj.child == C
+    assert Cj.coordinates == Matrix([q0_def, q1_def])
+    assert Cj.speeds == Matrix([u0_def, u1_def])
+    assert Cj.rotation_coordinate == q0_def
+    assert Cj.translation_coordinate == q1_def
+    assert Cj.rotation_speed == u0_def
+    assert Cj.translation_speed == u1_def
+    assert Cj.kdes == Matrix([u0_def - q0_def.diff(t), u1_def - q1_def.diff(t)])
+    assert Cj.joint_axis == N.x
+    assert Cj.child_point.pos_from(C.masscenter) == Vector(0)
+    assert Cj.parent_point.pos_from(P.masscenter) == Vector(0)
+    assert Cj.parent_point.pos_from(Cj._child_point) == -q1_def * N.x
+    assert C.masscenter.pos_from(P.masscenter) == q1_def * N.x
+    assert Cj.child_point.vel(N) == u1_def * N.x
+    assert A.ang_vel_in(N) == u0_def * N.x
+    assert Cj.parent_interframe == N
+    assert Cj.child_interframe == A
+    assert Cj.__str__() == 'CylindricalJoint: J  parent: P  child: C'
+
+    q0, q1, u0, u1 = dynamicsymbols('q0:2, u0:2')
+    l, m = symbols('l, m')
+    N, A, P, C, Pint, Cint = _generate_body(True)
+    Cj = CylindricalJoint('J', P, C, rotation_coordinate=q0, rotation_speed=u0,
+                          translation_speed=u1, parent_point=m * N.x,
+                          child_point=l * A.y, parent_interframe=Pint,
+                          child_interframe=Cint, joint_axis=2 * N.z)
+    assert Cj.coordinates == Matrix([q0, q1_def])
+    assert Cj.speeds == Matrix([u0, u1])
+    assert Cj.rotation_coordinate == q0
+    assert Cj.translation_coordinate == q1_def
+    assert Cj.rotation_speed == u0
+    assert Cj.translation_speed == u1
+    assert Cj.kdes == Matrix([u0 - q0.diff(t), u1 - q1_def.diff(t)])
+    assert Cj.joint_axis == 2 * N.z
+    assert Cj.child_point.pos_from(C.masscenter) == l * A.y
+    assert Cj.parent_point.pos_from(P.masscenter) == m * N.x
+    assert Cj.parent_point.pos_from(Cj._child_point) == -q1_def * N.z
+    assert C.masscenter.pos_from(
+        P.masscenter) == m * N.x + q1_def * N.z - l * A.y
+    assert C.masscenter.vel(N) == u1 * N.z - u0 * l * A.z
+    assert A.ang_vel_in(N) == u0 * N.z
+
+
+def test_planar_joint():
+    N, A, P, C = _generate_body()
+    q0_def, q1_def, q2_def = dynamicsymbols('q0:3_J')
+    u0_def, u1_def, u2_def = dynamicsymbols('u0:3_J')
+    Cj = PlanarJoint('J', P, C)
+    assert Cj.name == 'J'
+    assert Cj.parent == P
+    assert Cj.child == C
+    assert Cj.coordinates == Matrix([q0_def, q1_def, q2_def])
+    assert Cj.speeds == Matrix([u0_def, u1_def, u2_def])
+    assert Cj.rotation_coordinate == q0_def
+    assert Cj.planar_coordinates == Matrix([q1_def, q2_def])
+    assert Cj.rotation_speed == u0_def
+    assert Cj.planar_speeds == Matrix([u1_def, u2_def])
+    assert Cj.kdes == Matrix([u0_def - q0_def.diff(t), u1_def - q1_def.diff(t),
+                              u2_def - q2_def.diff(t)])
+    assert Cj.rotation_axis == N.x
+    assert Cj.planar_vectors == [N.y, N.z]
+    assert Cj.child_point.pos_from(C.masscenter) == Vector(0)
+    assert Cj.parent_point.pos_from(P.masscenter) == Vector(0)
+    r_P_C = q1_def * N.y + q2_def * N.z
+    assert Cj.parent_point.pos_from(Cj.child_point) == -r_P_C
+    assert C.masscenter.pos_from(P.masscenter) == r_P_C
+    assert Cj.child_point.vel(N) == u1_def * N.y + u2_def * N.z
+    assert A.ang_vel_in(N) == u0_def * N.x
+    assert Cj.parent_interframe == N
+    assert Cj.child_interframe == A
+    assert Cj.__str__() == 'PlanarJoint: J  parent: P  child: C'
+
+    q0, q1, q2, u0, u1, u2 = dynamicsymbols('q0:3, u0:3')
+    l, m = symbols('l, m')
+    N, A, P, C, Pint, Cint = _generate_body(True)
+    Cj = PlanarJoint('J', P, C, rotation_coordinate=q0,
+                     planar_coordinates=[q1, q2], planar_speeds=[u1, u2],
+                     parent_point=m * N.x, child_point=l * A.y,
+                     parent_interframe=Pint, child_interframe=Cint)
+    assert Cj.coordinates == Matrix([q0, q1, q2])
+    assert Cj.speeds == Matrix([u0_def, u1, u2])
+    assert Cj.rotation_coordinate == q0
+    assert Cj.planar_coordinates == Matrix([q1, q2])
+    assert Cj.rotation_speed == u0_def
+    assert Cj.planar_speeds == Matrix([u1, u2])
+    assert Cj.kdes == Matrix([u0_def - q0.diff(t), u1 - q1.diff(t),
+                              u2 - q2.diff(t)])
+    assert Cj.rotation_axis == Pint.x
+    assert Cj.planar_vectors == [Pint.y, Pint.z]
+    assert Cj.child_point.pos_from(C.masscenter) == l * A.y
+    assert Cj.parent_point.pos_from(P.masscenter) == m * N.x
+    assert Cj.parent_point.pos_from(Cj.child_point) == q1 * N.y + q2 * N.z
+    assert C.masscenter.pos_from(
+        P.masscenter) == m * N.x - q1 * N.y - q2 * N.z - l * A.y
+    assert C.masscenter.vel(N) == -u1 * N.y - u2 * N.z + u0_def * l * A.x
+    assert A.ang_vel_in(N) == u0_def * N.x
+
+
+def test_planar_joint_advanced():
+    # Tests whether someone is able to just specify two normals, which will form
+    # the rotation axis seen from the parent and child body.
+    # This specific example is a block on a slope, which has that same slope of
+    # 30 degrees, so in the zero configuration the frames of the parent and
+    # child are actually aligned.
+    q0, q1, q2, u0, u1, u2 = dynamicsymbols('q0:3, u0:3')
+    l1, l2 = symbols('l1:3')
+    N, A, P, C = _generate_body()
+    J = PlanarJoint('J', P, C, q0, [q1, q2], u0, [u1, u2],
+                    parent_point=l1 * N.z,
+                    child_point=-l2 * C.z,
+                    parent_interframe=N.z + N.y / sqrt(3),
+                    child_interframe=A.z + A.y / sqrt(3))
+    assert J.rotation_axis.express(N) == (N.z + N.y / sqrt(3)).normalize()
+    assert J.rotation_axis.express(A) == (A.z + A.y / sqrt(3)).normalize()
+    assert J.rotation_axis.angle_between(N.z) == pi / 6
+    assert N.dcm(A).xreplace({q0: 0, q1: 0, q2: 0}) == eye(3)
+    N_R_A = Matrix([
+        [cos(q0), -sqrt(3) * sin(q0) / 2, sin(q0) / 2],
+        [sqrt(3) * sin(q0) / 2, 3 * cos(q0) / 4 + 1 / 4,
+         sqrt(3) * (1 - cos(q0)) / 4],
+        [-sin(q0) / 2, sqrt(3) * (1 - cos(q0)) / 4, cos(q0) / 4 + 3 / 4]])
+    # N.dcm(A) == N_R_A did not work
+    assert _simplify_matrix(N.dcm(A) - N_R_A) == zeros(3)
+
+
+def test_spherical_joint():
+    N, A, P, C = _generate_body()
+    q0, q1, q2, u0, u1, u2 = dynamicsymbols('q0:3_S, u0:3_S')
+    S = SphericalJoint('S', P, C)
+    assert S.name == 'S'
+    assert S.parent == P
+    assert S.child == C
+    assert S.coordinates == Matrix([q0, q1, q2])
+    assert S.speeds == Matrix([u0, u1, u2])
+    assert S.kdes == Matrix([u0 - q0.diff(t), u1 - q1.diff(t), u2 - q2.diff(t)])
+    assert S.child_point.pos_from(C.masscenter) == Vector(0)
+    assert S.parent_point.pos_from(P.masscenter) == Vector(0)
+    assert S.parent_point.pos_from(S.child_point) == Vector(0)
+    assert P.masscenter.pos_from(C.masscenter) == Vector(0)
+    assert C.masscenter.vel(N) == Vector(0)
+    assert P.ang_vel_in(C) == (-u0 * cos(q1) * cos(q2) - u1 * sin(q2)) * A.x + (
+            u0 * sin(q2) * cos(q1) - u1 * cos(q2)) * A.y + (
+                   -u0 * sin(q1) - u2) * A.z
+    assert C.ang_vel_in(P) == (u0 * cos(q1) * cos(q2) + u1 * sin(q2)) * A.x + (
+            -u0 * sin(q2) * cos(q1) + u1 * cos(q2)) * A.y + (
+                   u0 * sin(q1) + u2) * A.z
+    assert S.__str__() == 'SphericalJoint: S  parent: P  child: C'
+    assert S._rot_type == 'BODY'
+    assert S._rot_order == 123
+    assert S._amounts is None
+
+
+def test_spherical_joint_speeds_as_derivative_terms():
+    # This tests checks whether the system remains valid if the user chooses to
+    # pass the derivative of the generalized coordinates as generalized speeds
+    q0, q1, q2 = dynamicsymbols('q0:3')
+    u0, u1, u2 = dynamicsymbols('q0:3', 1)
+    N, A, P, C = _generate_body()
+    S = SphericalJoint('S', P, C, coordinates=[q0, q1, q2], speeds=[u0, u1, u2])
+    assert S.coordinates == Matrix([q0, q1, q2])
+    assert S.speeds == Matrix([u0, u1, u2])
+    assert S.kdes == Matrix([0, 0, 0])
+    assert P.ang_vel_in(C) == (-u0 * cos(q1) * cos(q2) - u1 * sin(q2)) * A.x + (
+        u0 * sin(q2) * cos(q1) - u1 * cos(q2)) * A.y + (
+               -u0 * sin(q1) - u2) * A.z
+
+
+def test_spherical_joint_coords():
+    q0s, q1s, q2s, u0s, u1s, u2s = dynamicsymbols('q0:3_S, u0:3_S')
+    q0, q1, q2, q3, u0, u1, u2, u4 = dynamicsymbols('q0:4, u0:4')
+    # Test coordinates as list
+    N, A, P, C = _generate_body()
+    S = SphericalJoint('S', P, C, [q0, q1, q2], [u0, u1, u2])
+    assert S.coordinates == Matrix([q0, q1, q2])
+    assert S.speeds == Matrix([u0, u1, u2])
+    # Test coordinates as Matrix
+    N, A, P, C = _generate_body()
+    S = SphericalJoint('S', P, C, Matrix([q0, q1, q2]),
+                       Matrix([u0, u1, u2]))
+    assert S.coordinates == Matrix([q0, q1, q2])
+    assert S.speeds == Matrix([u0, u1, u2])
+    # Test too few generalized coordinates
+    N, A, P, C = _generate_body()
+    raises(ValueError,
+           lambda: SphericalJoint('S', P, C, Matrix([q0, q1]), Matrix([u0])))
+    # Test too many generalized coordinates
+    raises(ValueError, lambda: SphericalJoint(
+        'S', P, C, Matrix([q0, q1, q2, q3]), Matrix([u0, u1, u2])))
+    raises(ValueError, lambda: SphericalJoint(
+        'S', P, C, Matrix([q0, q1, q2]), Matrix([u0, u1, u2, u4])))
+
+
+def test_spherical_joint_orient_body():
+    q0, q1, q2, u0, u1, u2 = dynamicsymbols('q0:3, u0:3')
+    N_R_A = Matrix([
+        [-sin(q1), -sin(q2) * cos(q1), cos(q1) * cos(q2)],
+        [-sin(q0) * cos(q1), sin(q0) * sin(q1) * sin(q2) - cos(q0) * cos(q2),
+         -sin(q0) * sin(q1) * cos(q2) - sin(q2) * cos(q0)],
+        [cos(q0) * cos(q1), -sin(q0) * cos(q2) - sin(q1) * sin(q2) * cos(q0),
+         -sin(q0) * sin(q2) + sin(q1) * cos(q0) * cos(q2)]])
+    N_w_A = Matrix([[-u0 * sin(q1) - u2],
+                    [-u0 * sin(q2) * cos(q1) + u1 * cos(q2)],
+                    [u0 * cos(q1) * cos(q2) + u1 * sin(q2)]])
+    N_v_Co = Matrix([
+        [-sqrt(2) * (u0 * cos(q2 + pi / 4) * cos(q1) + u1 * sin(q2 + pi / 4))],
+        [-u0 * sin(q1) - u2], [-u0 * sin(q1) - u2]])
+    # Test default rot_type='BODY', rot_order=123
+    N, A, P, C, Pint, Cint = _generate_body(True)
+    S = SphericalJoint('S', P, C, coordinates=[q0, q1, q2], speeds=[u0, u1, u2],
+                       parent_point=N.x + N.y, child_point=-A.y + A.z,
+                       parent_interframe=Pint, child_interframe=Cint,
+                       rot_type='body', rot_order=123)
+    assert S._rot_type.upper() == 'BODY'
+    assert S._rot_order == 123
+    assert _simplify_matrix(N.dcm(A) - N_R_A) == zeros(3)
+    assert A.ang_vel_in(N).to_matrix(A) == N_w_A
+    assert C.masscenter.vel(N).to_matrix(A) == N_v_Co
+    # Test change of amounts
+    N, A, P, C, Pint, Cint = _generate_body(True)
+    S = SphericalJoint('S', P, C, coordinates=[q0, q1, q2], speeds=[u0, u1, u2],
+                       parent_point=N.x + N.y, child_point=-A.y + A.z,
+                       parent_interframe=Pint, child_interframe=Cint,
+                       rot_type='BODY', amounts=(q1, q0, q2), rot_order=123)
+    switch_order = lambda expr: expr.xreplace(
+        {q0: q1, q1: q0, q2: q2, u0: u1, u1: u0, u2: u2})
+    assert S._rot_type.upper() == 'BODY'
+    assert S._rot_order == 123
+    assert _simplify_matrix(N.dcm(A) - switch_order(N_R_A)) == zeros(3)
+    assert A.ang_vel_in(N).to_matrix(A) == switch_order(N_w_A)
+    assert C.masscenter.vel(N).to_matrix(A) == switch_order(N_v_Co)
+    # Test different rot_order
+    N, A, P, C, Pint, Cint = _generate_body(True)
+    S = SphericalJoint('S', P, C, coordinates=[q0, q1, q2], speeds=[u0, u1, u2],
+                       parent_point=N.x + N.y, child_point=-A.y + A.z,
+                       parent_interframe=Pint, child_interframe=Cint,
+                       rot_type='BodY', rot_order='yxz')
+    assert S._rot_type.upper() == 'BODY'
+    assert S._rot_order == 'yxz'
+    assert _simplify_matrix(N.dcm(A) - Matrix([
+        [-sin(q0) * cos(q1), sin(q0) * sin(q1) * cos(q2) - sin(q2) * cos(q0),
+         sin(q0) * sin(q1) * sin(q2) + cos(q0) * cos(q2)],
+        [-sin(q1), -cos(q1) * cos(q2), -sin(q2) * cos(q1)],
+        [cos(q0) * cos(q1), -sin(q0) * sin(q2) - sin(q1) * cos(q0) * cos(q2),
+         sin(q0) * cos(q2) - sin(q1) * sin(q2) * cos(q0)]])) == zeros(3)
+    assert A.ang_vel_in(N).to_matrix(A) == Matrix([
+        [u0 * sin(q1) - u2], [u0 * cos(q1) * cos(q2) - u1 * sin(q2)],
+        [u0 * sin(q2) * cos(q1) + u1 * cos(q2)]])
+    assert C.masscenter.vel(N).to_matrix(A) == Matrix([
+        [-sqrt(2) * (u0 * sin(q2 + pi / 4) * cos(q1) + u1 * cos(q2 + pi / 4))],
+        [u0 * sin(q1) - u2], [u0 * sin(q1) - u2]])
+
+
+def test_spherical_joint_orient_space():
+    q0, q1, q2, u0, u1, u2 = dynamicsymbols('q0:3, u0:3')
+    N_R_A = Matrix([
+        [-sin(q0) * sin(q2) - sin(q1) * cos(q0) * cos(q2),
+         sin(q0) * sin(q1) * cos(q2) - sin(q2) * cos(q0), cos(q1) * cos(q2)],
+        [-sin(q0) * cos(q2) + sin(q1) * sin(q2) * cos(q0),
+         -sin(q0) * sin(q1) * sin(q2) - cos(q0) * cos(q2), -sin(q2) * cos(q1)],
+        [cos(q0) * cos(q1), -sin(q0) * cos(q1), sin(q1)]])
+    N_w_A = Matrix([
+        [u1 * sin(q0) - u2 * cos(q0) * cos(q1)],
+        [u1 * cos(q0) + u2 * sin(q0) * cos(q1)], [u0 - u2 * sin(q1)]])
+    N_v_Co = Matrix([
+        [u0 - u2 * sin(q1)], [u0 - u2 * sin(q1)],
+        [sqrt(2) * (-u1 * sin(q0 + pi / 4) + u2 * cos(q0 + pi / 4) * cos(q1))]])
+    # Test default rot_type='BODY', rot_order=123
+    N, A, P, C, Pint, Cint = _generate_body(True)
+    S = SphericalJoint('S', P, C, coordinates=[q0, q1, q2], speeds=[u0, u1, u2],
+                       parent_point=N.x + N.z, child_point=-A.x + A.y,
+                       parent_interframe=Pint, child_interframe=Cint,
+                       rot_type='space', rot_order=123)
+    assert S._rot_type.upper() == 'SPACE'
+    assert S._rot_order == 123
+    assert _simplify_matrix(N.dcm(A) - N_R_A) == zeros(3)
+    assert _simplify_matrix(A.ang_vel_in(N).to_matrix(A)) == N_w_A
+    assert _simplify_matrix(C.masscenter.vel(N).to_matrix(A)) == N_v_Co
+    # Test change of amounts
+    switch_order = lambda expr: expr.xreplace(
+        {q0: q1, q1: q0, q2: q2, u0: u1, u1: u0, u2: u2})
+    N, A, P, C, Pint, Cint = _generate_body(True)
+    S = SphericalJoint('S', P, C, coordinates=[q0, q1, q2], speeds=[u0, u1, u2],
+                       parent_point=N.x + N.z, child_point=-A.x + A.y,
+                       parent_interframe=Pint, child_interframe=Cint,
+                       rot_type='SPACE', amounts=(q1, q0, q2), rot_order=123)
+    assert S._rot_type.upper() == 'SPACE'
+    assert S._rot_order == 123
+    assert _simplify_matrix(N.dcm(A) - switch_order(N_R_A)) == zeros(3)
+    assert _simplify_matrix(A.ang_vel_in(N).to_matrix(A)) == switch_order(N_w_A)
+    assert _simplify_matrix(C.masscenter.vel(N).to_matrix(A)) == switch_order(N_v_Co)
+    # Test different rot_order
+    N, A, P, C, Pint, Cint = _generate_body(True)
+    S = SphericalJoint('S', P, C, coordinates=[q0, q1, q2], speeds=[u0, u1, u2],
+                       parent_point=N.x + N.z, child_point=-A.x + A.y,
+                       parent_interframe=Pint, child_interframe=Cint,
+                       rot_type='SPaCe', rot_order='zxy')
+    assert S._rot_type.upper() == 'SPACE'
+    assert S._rot_order == 'zxy'
+    assert _simplify_matrix(N.dcm(A) - Matrix([
+        [-sin(q2) * cos(q1), -sin(q0) * cos(q2) + sin(q1) * sin(q2) * cos(q0),
+         sin(q0) * sin(q1) * sin(q2) + cos(q0) * cos(q2)],
+        [-sin(q1), -cos(q0) * cos(q1), -sin(q0) * cos(q1)],
+        [cos(q1) * cos(q2), -sin(q0) * sin(q2) - sin(q1) * cos(q0) * cos(q2),
+         -sin(q0) * sin(q1) * cos(q2) + sin(q2) * cos(q0)]]))
+    assert _simplify_matrix(A.ang_vel_in(N).to_matrix(A) - Matrix([
+        [-u0 + u2 * sin(q1)], [-u1 * sin(q0) + u2 * cos(q0) * cos(q1)],
+        [u1 * cos(q0) + u2 * sin(q0) * cos(q1)]])) == zeros(3, 1)
+    assert _simplify_matrix(C.masscenter.vel(N).to_matrix(A) - Matrix([
+        [u1 * cos(q0) + u2 * sin(q0) * cos(q1)],
+        [u1 * cos(q0) + u2 * sin(q0) * cos(q1)],
+        [u0 + u1 * sin(q0) - u2 * sin(q1) -
+         u2 * cos(q0) * cos(q1)]])) == zeros(3, 1)
+
+
+def test_weld_joint():
+    _, _, P, C = _generate_body()
+    W = WeldJoint('W', P, C)
+    assert W.name == 'W'
+    assert W.parent == P
+    assert W.child == C
+    assert W.coordinates == Matrix()
+    assert W.speeds == Matrix()
+    assert W.kdes == Matrix(1, 0, []).T
+    assert P.dcm(C) == eye(3)
+    assert W.child_point.pos_from(C.masscenter) == Vector(0)
+    assert W.parent_point.pos_from(P.masscenter) == Vector(0)
+    assert W.parent_point.pos_from(W.child_point) == Vector(0)
+    assert P.masscenter.pos_from(C.masscenter) == Vector(0)
+    assert C.masscenter.vel(P.frame) == Vector(0)
+    assert P.ang_vel_in(C) == 0
+    assert C.ang_vel_in(P) == 0
+    assert W.__str__() == 'WeldJoint: W  parent: P  child: C'
+
+    N, A, P, C = _generate_body()
+    l, m = symbols('l m')
+    Pint = ReferenceFrame('P_int')
+    Pint.orient_axis(P.frame, P.y, pi / 2)
+    W = WeldJoint('W', P, C, parent_point=l * P.frame.x,
+                  child_point=m * C.frame.y, parent_interframe=Pint)
+
+    assert W.child_point.pos_from(C.masscenter) == m * C.frame.y
+    assert W.parent_point.pos_from(P.masscenter) == l * P.frame.x
+    assert W.parent_point.pos_from(W.child_point) == Vector(0)
+    assert P.masscenter.pos_from(C.masscenter) == - l * N.x + m * A.y
+    assert C.masscenter.vel(P.frame) == Vector(0)
+    assert P.masscenter.vel(Pint) == Vector(0)
+    assert C.ang_vel_in(P) == 0
+    assert P.ang_vel_in(C) == 0
+    assert P.x == A.z
+
+    JointsMethod(P, W)  # Tests #10770
+
+
+def test_deprecated_parent_child_axis():
+    q, u = dynamicsymbols('q_J, u_J')
+    N, A, P, C = _generate_body()
+    with warns_deprecated_sympy():
+        PinJoint('J', P, C, child_axis=-A.x)
+    assert (-A.x).angle_between(N.x) == 0
+    assert -A.x.express(N) == N.x
+    assert A.dcm(N) == Matrix([[-1, 0, 0],
+                               [0, -cos(q), -sin(q)],
+                               [0, -sin(q), cos(q)]])
+    assert A.ang_vel_in(N) == u * N.x
+    assert A.ang_vel_in(N).magnitude() == sqrt(u ** 2)
+
+    N, A, P, C = _generate_body()
+    with warns_deprecated_sympy():
+        PrismaticJoint('J', P, C, parent_axis=P.x + P.y)
+    assert (A.x).angle_between(N.x + N.y) == 0
+    assert A.x.express(N) == (N.x + N.y) / sqrt(2)
+    assert A.dcm(N) == Matrix([[sqrt(2) / 2, sqrt(2) / 2, 0],
+                               [-sqrt(2) / 2, sqrt(2) / 2, 0], [0, 0, 1]])
+    assert A.ang_vel_in(N) == Vector(0)
+
+
+def test_deprecated_joint_pos():
+    N, A, P, C = _generate_body()
+    with warns_deprecated_sympy():
+        pin = PinJoint('J', P, C, parent_joint_pos=N.x + N.y,
+                       child_joint_pos=C.y - C.z)
+    assert pin.parent_point.pos_from(P.masscenter) == N.x + N.y
+    assert pin.child_point.pos_from(C.masscenter) == C.y - C.z
+
+    N, A, P, C = _generate_body()
+    with warns_deprecated_sympy():
+        slider = PrismaticJoint('J', P, C, parent_joint_pos=N.z + N.y,
+                                child_joint_pos=C.y - C.x)
+    assert slider.parent_point.pos_from(P.masscenter) == N.z + N.y
+    assert slider.child_point.pos_from(C.masscenter) == C.y - C.x

venv/lib/python3.10/site-packages/sympy/physics/mechanics/tests/test_jointsmethod.py

@@ -0,0 +1,212 @@
+from sympy.core.function import expand
+from sympy.core.symbol import symbols
+from sympy.functions.elementary.trigonometric import (cos, sin)
+from sympy.matrices.dense import Matrix
+from sympy.simplify.trigsimp import trigsimp
+from sympy.physics.mechanics import (PinJoint, JointsMethod, Body, KanesMethod,
+                                    PrismaticJoint, LagrangesMethod, inertia)
+from sympy.physics.vector import dynamicsymbols, ReferenceFrame
+from sympy.testing.pytest import raises
+from sympy.core.backend import zeros
+from sympy.utilities.lambdify import lambdify
+from sympy.solvers.solvers import solve
+
+
+t = dynamicsymbols._t # type: ignore
+
+
+def test_jointsmethod():
+    P = Body('P')
+    C = Body('C')
+    Pin = PinJoint('P1', P, C)
+    C_ixx, g = symbols('C_ixx g')
+    q, u = dynamicsymbols('q_P1, u_P1')
+    P.apply_force(g*P.y)
+    method = JointsMethod(P, Pin)
+    assert method.frame == P.frame
+    assert method.bodies == [C, P]
+    assert method.loads == [(P.masscenter, g*P.frame.y)]
+    assert method.q == Matrix([q])
+    assert method.u == Matrix([u])
+    assert method.kdes == Matrix([u - q.diff()])
+    soln = method.form_eoms()
+    assert soln == Matrix([[-C_ixx*u.diff()]])
+    assert method.forcing_full == Matrix([[u], [0]])
+    assert method.mass_matrix_full == Matrix([[1, 0], [0, C_ixx]])
+    assert isinstance(method.method, KanesMethod)
+
+def test_jointmethod_duplicate_coordinates_speeds():
+    P = Body('P')
+    C = Body('C')
+    T = Body('T')
+    q, u = dynamicsymbols('q u')
+    P1 = PinJoint('P1', P, C, q)
+    P2 = PrismaticJoint('P2', C, T, q)
+    raises(ValueError, lambda: JointsMethod(P, P1, P2))
+
+    P1 = PinJoint('P1', P, C, speeds=u)
+    P2 = PrismaticJoint('P2', C, T, speeds=u)
+    raises(ValueError, lambda: JointsMethod(P, P1, P2))
+
+    P1 = PinJoint('P1', P, C, q, u)
+    P2 = PrismaticJoint('P2', C, T, q, u)
+    raises(ValueError, lambda: JointsMethod(P, P1, P2))
+
+def test_complete_simple_double_pendulum():
+    q1, q2 = dynamicsymbols('q1 q2')
+    u1, u2 = dynamicsymbols('u1 u2')
+    m, l, g = symbols('m l g')
+    C = Body('C')  # ceiling
+    PartP = Body('P', mass=m)
+    PartR = Body('R', mass=m)
+    J1 = PinJoint('J1', C, PartP, speeds=u1, coordinates=q1,
+                  child_point=-l*PartP.x, joint_axis=C.z)
+    J2 = PinJoint('J2', PartP, PartR, speeds=u2, coordinates=q2,
+                  child_point=-l*PartR.x, joint_axis=PartP.z)
+
+    PartP.apply_force(m*g*C.x)
+    PartR.apply_force(m*g*C.x)
+
+    method = JointsMethod(C, J1, J2)
+    method.form_eoms()
+
+    assert expand(method.mass_matrix_full) == Matrix([[1, 0, 0, 0],
+                                                      [0, 1, 0, 0],
+                                                      [0, 0, 2*l**2*m*cos(q2) + 3*l**2*m, l**2*m*cos(q2) + l**2*m],
+                                                      [0, 0, l**2*m*cos(q2) + l**2*m, l**2*m]])
+    assert trigsimp(method.forcing_full) == trigsimp(Matrix([[u1], [u2], [-g*l*m*(sin(q1 + q2) + sin(q1)) -
+                                           g*l*m*sin(q1) + l**2*m*(2*u1 + u2)*u2*sin(q2)],
+                                          [-g*l*m*sin(q1 + q2) - l**2*m*u1**2*sin(q2)]]))
+
+def test_two_dof_joints():
+    q1, q2, u1, u2 = dynamicsymbols('q1 q2 u1 u2')
+    m, c1, c2, k1, k2 = symbols('m c1 c2 k1 k2')
+    W = Body('W')
+    B1 = Body('B1', mass=m)
+    B2 = Body('B2', mass=m)
+    J1 = PrismaticJoint('J1', W, B1, coordinates=q1, speeds=u1)
+    J2 = PrismaticJoint('J2', B1, B2, coordinates=q2, speeds=u2)
+    W.apply_force(k1*q1*W.x, reaction_body=B1)
+    W.apply_force(c1*u1*W.x, reaction_body=B1)
+    B1.apply_force(k2*q2*W.x, reaction_body=B2)
+    B1.apply_force(c2*u2*W.x, reaction_body=B2)
+    method = JointsMethod(W, J1, J2)
+    method.form_eoms()
+    MM = method.mass_matrix
+    forcing = method.forcing
+    rhs = MM.LUsolve(forcing)
+    assert expand(rhs[0]) == expand((-k1 * q1 - c1 * u1 + k2 * q2 + c2 * u2)/m)
+    assert expand(rhs[1]) == expand((k1 * q1 + c1 * u1 - 2 * k2 * q2 - 2 *
+                                    c2 * u2) / m)
+
+def test_simple_pedulum():
+    l, m, g = symbols('l m g')
+    C = Body('C')
+    b = Body('b', mass=m)
+    q = dynamicsymbols('q')
+    P = PinJoint('P', C, b, speeds=q.diff(t), coordinates=q,
+                 child_point=-l * b.x, joint_axis=C.z)
+    b.potential_energy = - m * g * l * cos(q)
+    method = JointsMethod(C, P)
+    method.form_eoms(LagrangesMethod)
+    rhs = method.rhs()
+    assert rhs[1] == -g*sin(q)/l
+
+def test_chaos_pendulum():
+    #https://www.pydy.org/examples/chaos_pendulum.html
+    mA, mB, lA, lB, IAxx, IBxx, IByy, IBzz, g = symbols('mA, mB, lA, lB, IAxx, IBxx, IByy, IBzz, g')
+    theta, phi, omega, alpha = dynamicsymbols('theta phi omega alpha')
+
+    A = ReferenceFrame('A')
+    B = ReferenceFrame('B')
+
+    rod = Body('rod', mass=mA, frame=A, central_inertia=inertia(A, IAxx, IAxx, 0))
+    plate = Body('plate', mass=mB, frame=B, central_inertia=inertia(B, IBxx, IByy, IBzz))
+    C = Body('C')
+    J1 = PinJoint('J1', C, rod, coordinates=theta, speeds=omega,
+                  child_point=-lA * rod.z, joint_axis=C.y)
+    J2 = PinJoint('J2', rod, plate, coordinates=phi, speeds=alpha,
+                  parent_point=(lB - lA) * rod.z, joint_axis=rod.z)
+
+    rod.apply_force(mA*g*C.z)
+    plate.apply_force(mB*g*C.z)
+
+    method = JointsMethod(C, J1, J2)
+    method.form_eoms()
+
+    MM = method.mass_matrix
+    forcing = method.forcing
+    rhs = MM.LUsolve(forcing)
+    xd = (-2 * IBxx * alpha * omega * sin(phi) * cos(phi) + 2 * IByy * alpha * omega * sin(phi) *
+            cos(phi) - g * lA * mA * sin(theta) - g * lB * mB * sin(theta)) / (IAxx + IBxx *
+                sin(phi)**2 + IByy * cos(phi)**2 + lA**2 * mA + lB**2 * mB)
+    assert (rhs[0] - xd).simplify() == 0
+    xd = (IBxx - IByy) * omega**2 * sin(phi) * cos(phi) / IBzz
+    assert (rhs[1] - xd).simplify() == 0
+
+def test_four_bar_linkage_with_manual_constraints():
+    q1, q2, q3, u1, u2, u3 = dynamicsymbols('q1:4, u1:4')
+    l1, l2, l3, l4, rho = symbols('l1:5, rho')
+
+    N = ReferenceFrame('N')
+    inertias = [inertia(N, 0, 0, rho * l ** 3 / 12) for l in (l1, l2, l3, l4)]
+    link1 = Body('Link1', frame=N, mass=rho * l1, central_inertia=inertias[0])
+    link2 = Body('Link2', mass=rho * l2, central_inertia=inertias[1])
+    link3 = Body('Link3', mass=rho * l3, central_inertia=inertias[2])
+    link4 = Body('Link4', mass=rho * l4, central_inertia=inertias[3])
+
+    joint1 = PinJoint(
+        'J1', link1, link2, coordinates=q1, speeds=u1, joint_axis=link1.z,
+        parent_point=l1 / 2 * link1.x, child_point=-l2 / 2 * link2.x)
+    joint2 = PinJoint(
+        'J2', link2, link3, coordinates=q2, speeds=u2, joint_axis=link2.z,
+        parent_point=l2 / 2 * link2.x, child_point=-l3 / 2 * link3.x)
+    joint3 = PinJoint(
+        'J3', link3, link4, coordinates=q3, speeds=u3, joint_axis=link3.z,
+        parent_point=l3 / 2 * link3.x, child_point=-l4 / 2 * link4.x)
+
+    loop = link4.masscenter.pos_from(link1.masscenter) \
+           + l1 / 2 * link1.x + l4 / 2 * link4.x
+
+    fh = Matrix([loop.dot(link1.x), loop.dot(link1.y)])
+
+    method = JointsMethod(link1, joint1, joint2, joint3)
+
+    t = dynamicsymbols._t
+    qdots = solve(method.kdes, [q1.diff(t), q2.diff(t), q3.diff(t)])
+    fhd = fh.diff(t).subs(qdots)
+
+    kane = KanesMethod(method.frame, q_ind=[q1], u_ind=[u1],
+                       q_dependent=[q2, q3], u_dependent=[u2, u3],
+                       kd_eqs=method.kdes, configuration_constraints=fh,
+                       velocity_constraints=fhd, forcelist=method.loads,
+                       bodies=method.bodies)
+    fr, frs = kane.kanes_equations()
+    assert fr == zeros(1)
+
+    # Numerically check the mass- and forcing-matrix
+    p = Matrix([l1, l2, l3, l4, rho])
+    q = Matrix([q1, q2, q3])
+    u = Matrix([u1, u2, u3])
+    eval_m = lambdify((q, p), kane.mass_matrix)
+    eval_f = lambdify((q, u, p), kane.forcing)
+    eval_fhd = lambdify((q, u, p), fhd)
+
+    p_vals = [0.13, 0.24, 0.21, 0.34, 997]
+    q_vals = [2.1, 0.6655470375077588, 2.527408138024188]  # Satisfies fh
+    u_vals = [0.2, -0.17963733938852067, 0.1309060540601612]  # Satisfies fhd
+    mass_check = Matrix([[3.452709815256506e+01, 7.003948798374735e+00,
+                          -4.939690970641498e+00],
+                         [-2.203792703880936e-14, 2.071702479957077e-01,
+                          2.842917573033711e-01],
+                         [-1.300000000000123e-01, -8.836934896046506e-03,
+                          1.864891330060847e-01]])
+    forcing_check = Matrix([[-0.031211821321648],
+                            [-0.00066022608181],
+                            [0.001813559741243]])
+    eps = 1e-10
+    assert all(abs(x) < eps for x in eval_fhd(q_vals, u_vals, p_vals))
+    assert all(abs(x) < eps for x in
+               (Matrix(eval_m(q_vals, p_vals)) - mass_check))
+    assert all(abs(x) < eps for x in
+               (Matrix(eval_f(q_vals, u_vals, p_vals)) - forcing_check))

venv/lib/python3.10/site-packages/sympy/physics/mechanics/tests/test_kane.py

@@ -0,0 +1,532 @@
+from sympy import solve
+from sympy.core.backend import (cos, expand, Matrix, sin, symbols, tan, sqrt, S,
+                                zeros, eye)
+from sympy.simplify.simplify import simplify
+from sympy.physics.mechanics import (dynamicsymbols, ReferenceFrame, Point,
+                                     RigidBody, KanesMethod, inertia, Particle,
+                                     dot)
+from sympy.testing.pytest import raises
+from sympy.core.backend import USE_SYMENGINE
+
+
+def test_invalid_coordinates():
+    # Simple pendulum, but use symbols instead of dynamicsymbols
+    l, m, g = symbols('l m g')
+    q, u = symbols('q u')  # Generalized coordinate
+    kd = [q.diff(dynamicsymbols._t) - u]
+    N, O = ReferenceFrame('N'), Point('O')
+    O.set_vel(N, 0)
+    P = Particle('P', Point('P'), m)
+    P.point.set_pos(O, l * (sin(q) * N.x - cos(q) * N.y))
+    F = (P.point, -m * g * N.y)
+    raises(ValueError, lambda: KanesMethod(N, [q], [u], kd, bodies=[P],
+                                           forcelist=[F]))
+
+
+def test_one_dof():
+    # This is for a 1 dof spring-mass-damper case.
+    # It is described in more detail in the KanesMethod docstring.
+    q, u = dynamicsymbols('q u')
+    qd, ud = dynamicsymbols('q u', 1)
+    m, c, k = symbols('m c k')
+    N = ReferenceFrame('N')
+    P = Point('P')
+    P.set_vel(N, u * N.x)
+
+    kd = [qd - u]
+    FL = [(P, (-k * q - c * u) * N.x)]
+    pa = Particle('pa', P, m)
+    BL = [pa]
+
+    KM = KanesMethod(N, [q], [u], kd)
+    KM.kanes_equations(BL, FL)
+
+    assert KM.bodies == BL
+    assert KM.loads == FL
+
+    MM = KM.mass_matrix
+    forcing = KM.forcing
+    rhs = MM.inv() * forcing
+    assert expand(rhs[0]) == expand(-(q * k + u * c) / m)
+
+    assert simplify(KM.rhs() -
+                    KM.mass_matrix_full.LUsolve(KM.forcing_full)) == zeros(2, 1)
+
+    assert (KM.linearize(A_and_B=True, )[0] == Matrix([[0, 1], [-k/m, -c/m]]))
+
+
+def test_two_dof():
+    # This is for a 2 d.o.f., 2 particle spring-mass-damper.
+    # The first coordinate is the displacement of the first particle, and the
+    # second is the relative displacement between the first and second
+    # particles. Speeds are defined as the time derivatives of the particles.
+    q1, q2, u1, u2 = dynamicsymbols('q1 q2 u1 u2')
+    q1d, q2d, u1d, u2d = dynamicsymbols('q1 q2 u1 u2', 1)
+    m, c1, c2, k1, k2 = symbols('m c1 c2 k1 k2')
+    N = ReferenceFrame('N')
+    P1 = Point('P1')
+    P2 = Point('P2')
+    P1.set_vel(N, u1 * N.x)
+    P2.set_vel(N, (u1 + u2) * N.x)
+    # Note we multiply the kinematic equation by an arbitrary factor
+    # to test the implicit vs explicit kinematics attribute
+    kd = [q1d/2 - u1/2, 2*q2d - 2*u2]
+
+    # Now we create the list of forces, then assign properties to each
+    # particle, then create a list of all particles.
+    FL = [(P1, (-k1 * q1 - c1 * u1 + k2 * q2 + c2 * u2) * N.x), (P2, (-k2 *
+        q2 - c2 * u2) * N.x)]
+    pa1 = Particle('pa1', P1, m)
+    pa2 = Particle('pa2', P2, m)
+    BL = [pa1, pa2]
+
+    # Finally we create the KanesMethod object, specify the inertial frame,
+    # pass relevant information, and form Fr & Fr*. Then we calculate the mass
+    # matrix and forcing terms, and finally solve for the udots.
+    KM = KanesMethod(N, q_ind=[q1, q2], u_ind=[u1, u2], kd_eqs=kd)
+    KM.kanes_equations(BL, FL)
+    MM = KM.mass_matrix
+    forcing = KM.forcing
+    rhs = MM.inv() * forcing
+    assert expand(rhs[0]) == expand((-k1 * q1 - c1 * u1 + k2 * q2 + c2 * u2)/m)
+    assert expand(rhs[1]) == expand((k1 * q1 + c1 * u1 - 2 * k2 * q2 - 2 *
+                                    c2 * u2) / m)
+
+    # Check that the explicit form is the default and kinematic mass matrix is identity
+    assert KM.explicit_kinematics
+    assert KM.mass_matrix_kin == eye(2)
+
+    # Check that for the implicit form the mass matrix is not identity
+    KM.explicit_kinematics = False
+    assert KM.mass_matrix_kin == Matrix([[S(1)/2, 0], [0, 2]])
+
+    # Check that whether using implicit or explicit kinematics the RHS
+    # equations are consistent with the matrix form
+    for explicit_kinematics in [False, True]:
+        KM.explicit_kinematics = explicit_kinematics
+        assert simplify(KM.rhs() -
+                        KM.mass_matrix_full.LUsolve(KM.forcing_full)) == zeros(4, 1)
+
+    # Make sure an error is raised if nonlinear kinematic differential
+    # equations are supplied.
+    kd = [q1d - u1**2, sin(q2d) - cos(u2)]
+    raises(ValueError, lambda: KanesMethod(N, q_ind=[q1, q2],
+                                           u_ind=[u1, u2], kd_eqs=kd))
+
+def test_pend():
+    q, u = dynamicsymbols('q u')
+    qd, ud = dynamicsymbols('q u', 1)
+    m, l, g = symbols('m l g')
+    N = ReferenceFrame('N')
+    P = Point('P')
+    P.set_vel(N, -l * u * sin(q) * N.x + l * u * cos(q) * N.y)
+    kd = [qd - u]
+
+    FL = [(P, m * g * N.x)]
+    pa = Particle('pa', P, m)
+    BL = [pa]
+
+    KM = KanesMethod(N, [q], [u], kd)
+    KM.kanes_equations(BL, FL)
+    MM = KM.mass_matrix
+    forcing = KM.forcing
+    rhs = MM.inv() * forcing
+    rhs.simplify()
+    assert expand(rhs[0]) == expand(-g / l * sin(q))
+    assert simplify(KM.rhs() -
+                    KM.mass_matrix_full.LUsolve(KM.forcing_full)) == zeros(2, 1)
+
+
+def test_rolling_disc():
+    # Rolling Disc Example
+    # Here the rolling disc is formed from the contact point up, removing the
+    # need to introduce generalized speeds. Only 3 configuration and three
+    # speed variables are need to describe this system, along with the disc's
+    # mass and radius, and the local gravity (note that mass will drop out).
+    q1, q2, q3, u1, u2, u3 = dynamicsymbols('q1 q2 q3 u1 u2 u3')
+    q1d, q2d, q3d, u1d, u2d, u3d = dynamicsymbols('q1 q2 q3 u1 u2 u3', 1)
+    r, m, g = symbols('r m g')
+
+    # The kinematics are formed by a series of simple rotations. Each simple
+    # rotation creates a new frame, and the next rotation is defined by the new
+    # frame's basis vectors. This example uses a 3-1-2 series of rotations, or
+    # Z, X, Y series of rotations. Angular velocity for this is defined using
+    # the second frame's basis (the lean frame).
+    N = ReferenceFrame('N')
+    Y = N.orientnew('Y', 'Axis', [q1, N.z])
+    L = Y.orientnew('L', 'Axis', [q2, Y.x])
+    R = L.orientnew('R', 'Axis', [q3, L.y])
+    w_R_N_qd = R.ang_vel_in(N)
+    R.set_ang_vel(N, u1 * L.x + u2 * L.y + u3 * L.z)
+
+    # This is the translational kinematics. We create a point with no velocity
+    # in N; this is the contact point between the disc and ground. Next we form
+    # the position vector from the contact point to the disc's center of mass.
+    # Finally we form the velocity and acceleration of the disc.
+    C = Point('C')
+    C.set_vel(N, 0)
+    Dmc = C.locatenew('Dmc', r * L.z)
+    Dmc.v2pt_theory(C, N, R)
+
+    # This is a simple way to form the inertia dyadic.
+    I = inertia(L, m / 4 * r**2, m / 2 * r**2, m / 4 * r**2)
+
+    # Kinematic differential equations; how the generalized coordinate time
+    # derivatives relate to generalized speeds.
+    kd = [dot(R.ang_vel_in(N) - w_R_N_qd, uv) for uv in L]
+
+    # Creation of the force list; it is the gravitational force at the mass
+    # center of the disc. Then we create the disc by assigning a Point to the
+    # center of mass attribute, a ReferenceFrame to the frame attribute, and mass
+    # and inertia. Then we form the body list.
+    ForceList = [(Dmc, - m * g * Y.z)]
+    BodyD = RigidBody('BodyD', Dmc, R, m, (I, Dmc))
+    BodyList = [BodyD]
+
+    # Finally we form the equations of motion, using the same steps we did
+    # before. Specify inertial frame, supply generalized speeds, supply
+    # kinematic differential equation dictionary, compute Fr from the force
+    # list and Fr* from the body list, compute the mass matrix and forcing
+    # terms, then solve for the u dots (time derivatives of the generalized
+    # speeds).
+    KM = KanesMethod(N, q_ind=[q1, q2, q3], u_ind=[u1, u2, u3], kd_eqs=kd)
+    KM.kanes_equations(BodyList, ForceList)
+    MM = KM.mass_matrix
+    forcing = KM.forcing
+    rhs = MM.inv() * forcing
+    kdd = KM.kindiffdict()
+    rhs = rhs.subs(kdd)
+    rhs.simplify()
+    assert rhs.expand() == Matrix([(6*u2*u3*r - u3**2*r*tan(q2) +
+        4*g*sin(q2))/(5*r), -2*u1*u3/3, u1*(-2*u2 + u3*tan(q2))]).expand()
+    assert simplify(KM.rhs() -
+                    KM.mass_matrix_full.LUsolve(KM.forcing_full)) == zeros(6, 1)
+
+    # This code tests our output vs. benchmark values. When r=g=m=1, the
+    # critical speed (where all eigenvalues of the linearized equations are 0)
+    # is 1 / sqrt(3) for the upright case.
+    A = KM.linearize(A_and_B=True)[0]
+    A_upright = A.subs({r: 1, g: 1, m: 1}).subs({q1: 0, q2: 0, q3: 0, u1: 0, u3: 0})
+    import sympy
+    assert sympy.sympify(A_upright.subs({u2: 1 / sqrt(3)})).eigenvals() == {S.Zero: 6}
+
+
+def test_aux():
+    # Same as above, except we have 2 auxiliary speeds for the ground contact
+    # point, which is known to be zero. In one case, we go through then
+    # substitute the aux. speeds in at the end (they are zero, as well as their
+    # derivative), in the other case, we use the built-in auxiliary speed part
+    # of KanesMethod. The equations from each should be the same.
+    q1, q2, q3, u1, u2, u3 = dynamicsymbols('q1 q2 q3 u1 u2 u3')
+    q1d, q2d, q3d, u1d, u2d, u3d = dynamicsymbols('q1 q2 q3 u1 u2 u3', 1)
+    u4, u5, f1, f2 = dynamicsymbols('u4, u5, f1, f2')
+    u4d, u5d = dynamicsymbols('u4, u5', 1)
+    r, m, g = symbols('r m g')
+
+    N = ReferenceFrame('N')
+    Y = N.orientnew('Y', 'Axis', [q1, N.z])
+    L = Y.orientnew('L', 'Axis', [q2, Y.x])
+    R = L.orientnew('R', 'Axis', [q3, L.y])
+    w_R_N_qd = R.ang_vel_in(N)
+    R.set_ang_vel(N, u1 * L.x + u2 * L.y + u3 * L.z)
+
+    C = Point('C')
+    C.set_vel(N, u4 * L.x + u5 * (Y.z ^ L.x))
+    Dmc = C.locatenew('Dmc', r * L.z)
+    Dmc.v2pt_theory(C, N, R)
+    Dmc.a2pt_theory(C, N, R)
+
+    I = inertia(L, m / 4 * r**2, m / 2 * r**2, m / 4 * r**2)
+
+    kd = [dot(R.ang_vel_in(N) - w_R_N_qd, uv) for uv in L]
+
+    ForceList = [(Dmc, - m * g * Y.z), (C, f1 * L.x + f2 * (Y.z ^ L.x))]
+    BodyD = RigidBody('BodyD', Dmc, R, m, (I, Dmc))
+    BodyList = [BodyD]
+
+    KM = KanesMethod(N, q_ind=[q1, q2, q3], u_ind=[u1, u2, u3, u4, u5],
+                     kd_eqs=kd)
+    (fr, frstar) = KM.kanes_equations(BodyList, ForceList)
+    fr = fr.subs({u4d: 0, u5d: 0}).subs({u4: 0, u5: 0})
+    frstar = frstar.subs({u4d: 0, u5d: 0}).subs({u4: 0, u5: 0})
+
+    KM2 = KanesMethod(N, q_ind=[q1, q2, q3], u_ind=[u1, u2, u3], kd_eqs=kd,
+                      u_auxiliary=[u4, u5])
+    (fr2, frstar2) = KM2.kanes_equations(BodyList, ForceList)
+    fr2 = fr2.subs({u4d: 0, u5d: 0}).subs({u4: 0, u5: 0})
+    frstar2 = frstar2.subs({u4d: 0, u5d: 0}).subs({u4: 0, u5: 0})
+
+    frstar.simplify()
+    frstar2.simplify()
+
+    assert (fr - fr2).expand() == Matrix([0, 0, 0, 0, 0])
+    assert (frstar - frstar2).expand() == Matrix([0, 0, 0, 0, 0])
+
+
+def test_parallel_axis():
+    # This is for a 2 dof inverted pendulum on a cart.
+    # This tests the parallel axis code in KanesMethod. The inertia of the
+    # pendulum is defined about the hinge, not about the center of mass.
+
+    # Defining the constants and knowns of the system
+    gravity = symbols('g')
+    k, ls = symbols('k ls')
+    a, mA, mC = symbols('a mA mC')
+    F = dynamicsymbols('F')
+    Ix, Iy, Iz = symbols('Ix Iy Iz')
+
+    # Declaring the Generalized coordinates and speeds
+    q1, q2 = dynamicsymbols('q1 q2')
+    q1d, q2d = dynamicsymbols('q1 q2', 1)
+    u1, u2 = dynamicsymbols('u1 u2')
+    u1d, u2d = dynamicsymbols('u1 u2', 1)
+
+    # Creating reference frames
+    N = ReferenceFrame('N')
+    A = ReferenceFrame('A')
+
+    A.orient(N, 'Axis', [-q2, N.z])
+    A.set_ang_vel(N, -u2 * N.z)
+
+    # Origin of Newtonian reference frame
+    O = Point('O')
+
+    # Creating and Locating the positions of the cart, C, and the
+    # center of mass of the pendulum, A
+    C = O.locatenew('C', q1 * N.x)
+    Ao = C.locatenew('Ao', a * A.y)
+
+    # Defining velocities of the points
+    O.set_vel(N, 0)
+    C.set_vel(N, u1 * N.x)
+    Ao.v2pt_theory(C, N, A)
+    Cart = Particle('Cart', C, mC)
+    Pendulum = RigidBody('Pendulum', Ao, A, mA, (inertia(A, Ix, Iy, Iz), C))
+
+    # kinematical differential equations
+
+    kindiffs = [q1d - u1, q2d - u2]
+
+    bodyList = [Cart, Pendulum]
+
+    forceList = [(Ao, -N.y * gravity * mA),
+                 (C, -N.y * gravity * mC),
+                 (C, -N.x * k * (q1 - ls)),
+                 (C, N.x * F)]
+
+    km = KanesMethod(N, [q1, q2], [u1, u2], kindiffs)
+    (fr, frstar) = km.kanes_equations(bodyList, forceList)
+    mm = km.mass_matrix_full
+    assert mm[3, 3] == Iz
+
+def test_input_format():
+    # 1 dof problem from test_one_dof
+    q, u = dynamicsymbols('q u')
+    qd, ud = dynamicsymbols('q u', 1)
+    m, c, k = symbols('m c k')
+    N = ReferenceFrame('N')
+    P = Point('P')
+    P.set_vel(N, u * N.x)
+
+    kd = [qd - u]
+    FL = [(P, (-k * q - c * u) * N.x)]
+    pa = Particle('pa', P, m)
+    BL = [pa]
+
+    KM = KanesMethod(N, [q], [u], kd)
+    # test for input format kane.kanes_equations((body1, body2, particle1))
+    assert KM.kanes_equations(BL)[0] == Matrix([0])
+    # test for input format kane.kanes_equations(bodies=(body1, body 2), loads=(load1,load2))
+    assert KM.kanes_equations(bodies=BL, loads=None)[0] == Matrix([0])
+    # test for input format kane.kanes_equations(bodies=(body1, body 2), loads=None)
+    assert KM.kanes_equations(BL, loads=None)[0] == Matrix([0])
+    # test for input format kane.kanes_equations(bodies=(body1, body 2))
+    assert KM.kanes_equations(BL)[0] == Matrix([0])
+    # test for input format kane.kanes_equations(bodies=(body1, body2), loads=[])
+    assert KM.kanes_equations(BL, [])[0] == Matrix([0])
+    # test for error raised when a wrong force list (in this case a string) is provided
+    raises(ValueError, lambda: KM._form_fr('bad input'))
+
+    # 1 dof problem from test_one_dof with FL & BL in instance
+    KM = KanesMethod(N, [q], [u], kd, bodies=BL, forcelist=FL)
+    assert KM.kanes_equations()[0] == Matrix([-c*u - k*q])
+
+    # 2 dof problem from test_two_dof
+    q1, q2, u1, u2 = dynamicsymbols('q1 q2 u1 u2')
+    q1d, q2d, u1d, u2d = dynamicsymbols('q1 q2 u1 u2', 1)
+    m, c1, c2, k1, k2 = symbols('m c1 c2 k1 k2')
+    N = ReferenceFrame('N')
+    P1 = Point('P1')
+    P2 = Point('P2')
+    P1.set_vel(N, u1 * N.x)
+    P2.set_vel(N, (u1 + u2) * N.x)
+    kd = [q1d - u1, q2d - u2]
+
+    FL = ((P1, (-k1 * q1 - c1 * u1 + k2 * q2 + c2 * u2) * N.x), (P2, (-k2 *
+        q2 - c2 * u2) * N.x))
+    pa1 = Particle('pa1', P1, m)
+    pa2 = Particle('pa2', P2, m)
+    BL = (pa1, pa2)
+
+    KM = KanesMethod(N, q_ind=[q1, q2], u_ind=[u1, u2], kd_eqs=kd)
+    # test for input format
+    # kane.kanes_equations((body1, body2), (load1, load2))
+    KM.kanes_equations(BL, FL)
+    MM = KM.mass_matrix
+    forcing = KM.forcing
+    rhs = MM.inv() * forcing
+    assert expand(rhs[0]) == expand((-k1 * q1 - c1 * u1 + k2 * q2 + c2 * u2)/m)
+    assert expand(rhs[1]) == expand((k1 * q1 + c1 * u1 - 2 * k2 * q2 - 2 *
+                                    c2 * u2) / m)
+
+
+def test_implicit_kinematics():
+    # Test that implicit kinematics can handle complicated
+    # equations that explicit form struggles with
+    # See https://github.com/sympy/sympy/issues/22626
+
+    # Inertial frame
+    NED = ReferenceFrame('NED')
+    NED_o = Point('NED_o')
+    NED_o.set_vel(NED, 0)
+
+    # body frame
+    q_att = dynamicsymbols('lambda_0:4', real=True)
+    B = NED.orientnew('B', 'Quaternion', q_att)
+
+    # Generalized coordinates
+    q_pos = dynamicsymbols('B_x:z')
+    B_cm = NED_o.locatenew('B_cm', q_pos[0]*B.x + q_pos[1]*B.y + q_pos[2]*B.z)
+
+    q_ind = q_att[1:] + q_pos
+    q_dep = [q_att[0]]
+
+    kinematic_eqs = []
+
+    # Generalized velocities
+    B_ang_vel = B.ang_vel_in(NED)
+    P, Q, R = dynamicsymbols('P Q R')
+    B.set_ang_vel(NED, P*B.x + Q*B.y + R*B.z)
+
+    B_ang_vel_kd = (B.ang_vel_in(NED) - B_ang_vel).simplify()
+
+    # Equating the two gives us the kinematic equation
+    kinematic_eqs += [
+        B_ang_vel_kd & B.x,
+        B_ang_vel_kd & B.y,
+        B_ang_vel_kd & B.z
+    ]
+
+    B_cm_vel = B_cm.vel(NED)
+    U, V, W = dynamicsymbols('U V W')
+    B_cm.set_vel(NED, U*B.x + V*B.y + W*B.z)
+
+    # Compute the velocity of the point using the two methods
+    B_ref_vel_kd = (B_cm.vel(NED) - B_cm_vel)
+
+    # taking dot product with unit vectors to get kinematic equations
+    # relating body coordinates and velocities
+
+    # Note, there is a choice to dot with NED.xyz here. That makes
+    # the implicit form have some bigger terms but is still fine, the
+    # explicit form still struggles though
+    kinematic_eqs += [
+                      B_ref_vel_kd & B.x,
+                      B_ref_vel_kd & B.y,
+                      B_ref_vel_kd & B.z,
+                     ]
+
+    u_ind = [U, V, W, P, Q, R]
+
+    # constraints
+    q_att_vec = Matrix(q_att)
+    config_cons = [(q_att_vec.T*q_att_vec)[0] - 1] #unit norm
+    kinematic_eqs = kinematic_eqs + [(q_att_vec.T * q_att_vec.diff())[0]]
+
+    try:
+        KM = KanesMethod(NED, q_ind, u_ind,
+          q_dependent= q_dep,
+          kd_eqs = kinematic_eqs,
+          configuration_constraints = config_cons,
+          velocity_constraints= [],
+          u_dependent= [], #no dependent speeds
+          u_auxiliary = [], # No auxiliary speeds
+          explicit_kinematics = False # implicit kinematics
+        )
+    except Exception as e:
+        # symengine struggles with these kinematic equations
+        if USE_SYMENGINE and 'Matrix is rank deficient' in str(e):
+            return
+        else:
+            raise e
+
+    # mass and inertia dyadic relative to CM
+    M_B = symbols('M_B')
+    J_B = inertia(B, *[S(f'J_B_{ax}')*(1 if ax[0] == ax[1] else -1)
+            for ax in ['xx', 'yy', 'zz', 'xy', 'yz', 'xz']])
+    J_B = J_B.subs({S('J_B_xy'): 0, S('J_B_yz'): 0})
+    RB = RigidBody('RB', B_cm, B, M_B, (J_B, B_cm))
+
+    rigid_bodies = [RB]
+    # Forces
+    force_list = [
+        #gravity pointing down
+        (RB.masscenter, RB.mass*S('g')*NED.z),
+        #generic forces and torques in body frame(inputs)
+        (RB.frame, dynamicsymbols('T_z')*B.z),
+        (RB.masscenter, dynamicsymbols('F_z')*B.z)
+    ]
+
+    KM.kanes_equations(rigid_bodies, force_list)
+
+    # Expecting implicit form to be less than 5% of the flops
+    n_ops_implicit = sum(
+        [x.count_ops() for x in KM.forcing_full] +
+        [x.count_ops() for x in KM.mass_matrix_full]
+    )
+    # Save implicit kinematic matrices to use later
+    mass_matrix_kin_implicit = KM.mass_matrix_kin
+    forcing_kin_implicit = KM.forcing_kin
+
+    KM.explicit_kinematics = True
+    n_ops_explicit = sum(
+        [x.count_ops() for x in KM.forcing_full] +
+        [x.count_ops() for x in KM.mass_matrix_full]
+    )
+    forcing_kin_explicit = KM.forcing_kin
+
+    assert n_ops_implicit / n_ops_explicit < .05
+
+    # Ideally we would check that implicit and explicit equations give the same result as done in test_one_dof
+    # But the whole raison-d'etre of the implicit equations is to deal with problems such
+    # as this one where the explicit form is too complicated to handle, especially the angular part
+    # (i.e. tests would be too slow)
+    # Instead, we check that the kinematic equations are correct using more fundamental tests:
+    #
+    # (1) that we recover the kinematic equations we have provided
+    assert (mass_matrix_kin_implicit * KM.q.diff() - forcing_kin_implicit) == Matrix(kinematic_eqs)
+
+    # (2) that rate of quaternions matches what 'textbook' solutions give
+    # Note that we just use the explicit kinematics for the linear velocities
+    # as they are not as complicated as the angular ones
+    qdot_candidate = forcing_kin_explicit
+
+    quat_dot_textbook = Matrix([
+        [0, -P, -Q, -R],
+        [P,  0,  R, -Q],
+        [Q, -R,  0,  P],
+        [R,  Q, -P,  0],
+    ]) * q_att_vec / 2
+
+    # Again, if we don't use this "textbook" solution
+    # sympy will struggle to deal with the terms related to quaternion rates
+    # due to the number of operations involved
+    qdot_candidate[-1] = quat_dot_textbook[0] # lambda_0, note the [-1] as sympy's Kane puts the dependent coordinate last
+    qdot_candidate[0]  = quat_dot_textbook[1] # lambda_1
+    qdot_candidate[1]  = quat_dot_textbook[2] # lambda_2
+    qdot_candidate[2]  = quat_dot_textbook[3] # lambda_3
+
+    # sub the config constraint in the candidate solution and compare to the implicit rhs
+    lambda_0_sol = solve(config_cons[0], q_att_vec[0])[1]
+    lhs_candidate = simplify(mass_matrix_kin_implicit * qdot_candidate).subs({q_att_vec[0]: lambda_0_sol})
+    assert lhs_candidate == forcing_kin_implicit

venv/lib/python3.10/site-packages/sympy/physics/mechanics/tests/test_kane2.py

@@ -0,0 +1,462 @@
+from sympy.core.backend import cos, Matrix, sin, zeros, tan, pi, symbols
+from sympy.simplify.simplify import simplify
+from sympy.simplify.trigsimp import trigsimp
+from sympy.solvers.solvers import solve
+from sympy.physics.mechanics import (cross, dot, dynamicsymbols,
+                                     find_dynamicsymbols, KanesMethod, inertia,
+                                     inertia_of_point_mass, Point,
+                                     ReferenceFrame, RigidBody)
+
+
+def test_aux_dep():
+    # This test is about rolling disc dynamics, comparing the results found
+    # with KanesMethod to those found when deriving the equations "manually"
+    # with SymPy.
+    # The terms Fr, Fr*, and Fr*_steady are all compared between the two
+    # methods. Here, Fr*_steady refers to the generalized inertia forces for an
+    # equilibrium configuration.
+    # Note: comparing to the test of test_rolling_disc() in test_kane.py, this
+    # test also tests auxiliary speeds and configuration and motion constraints
+    #, seen in  the generalized dependent coordinates q[3], and depend speeds
+    # u[3], u[4] and u[5].
+
+
+    # First, manual derivation of Fr, Fr_star, Fr_star_steady.
+
+    # Symbols for time and constant parameters.
+    # Symbols for contact forces: Fx, Fy, Fz.
+    t, r, m, g, I, J = symbols('t r m g I J')
+    Fx, Fy, Fz = symbols('Fx Fy Fz')
+
+    # Configuration variables and their time derivatives:
+    # q[0] -- yaw
+    # q[1] -- lean
+    # q[2] -- spin
+    # q[3] -- dot(-r*B.z, A.z) -- distance from ground plane to disc center in
+    #         A.z direction
+    # Generalized speeds and their time derivatives:
+    # u[0] -- disc angular velocity component, disc fixed x direction
+    # u[1] -- disc angular velocity component, disc fixed y direction
+    # u[2] -- disc angular velocity component, disc fixed z direction
+    # u[3] -- disc velocity component, A.x direction
+    # u[4] -- disc velocity component, A.y direction
+    # u[5] -- disc velocity component, A.z direction
+    # Auxiliary generalized speeds:
+    # ua[0] -- contact point auxiliary generalized speed, A.x direction
+    # ua[1] -- contact point auxiliary generalized speed, A.y direction
+    # ua[2] -- contact point auxiliary generalized speed, A.z direction
+    q = dynamicsymbols('q:4')
+    qd = [qi.diff(t) for qi in q]
+    u = dynamicsymbols('u:6')
+    ud = [ui.diff(t) for ui in u]
+    ud_zero = dict(zip(ud, [0.]*len(ud)))
+    ua = dynamicsymbols('ua:3')
+    ua_zero = dict(zip(ua, [0.]*len(ua))) # noqa:F841
+
+    # Reference frames:
+    # Yaw intermediate frame: A.
+    # Lean intermediate frame: B.
+    # Disc fixed frame: C.
+    N = ReferenceFrame('N')
+    A = N.orientnew('A', 'Axis', [q[0], N.z])
+    B = A.orientnew('B', 'Axis', [q[1], A.x])
+    C = B.orientnew('C', 'Axis', [q[2], B.y])
+
+    # Angular velocity and angular acceleration of disc fixed frame
+    # u[0], u[1] and u[2] are generalized independent speeds.
+    C.set_ang_vel(N, u[0]*B.x + u[1]*B.y + u[2]*B.z)
+    C.set_ang_acc(N, C.ang_vel_in(N).diff(t, B)
+                   + cross(B.ang_vel_in(N), C.ang_vel_in(N)))
+
+    # Velocity and acceleration of points:
+    # Disc-ground contact point: P.
+    # Center of disc: O, defined from point P with depend coordinate: q[3]
+    # u[3], u[4] and u[5] are generalized dependent speeds.
+    P = Point('P')
+    P.set_vel(N, ua[0]*A.x + ua[1]*A.y + ua[2]*A.z)
+    O = P.locatenew('O', q[3]*A.z + r*sin(q[1])*A.y)
+    O.set_vel(N, u[3]*A.x + u[4]*A.y + u[5]*A.z)
+    O.set_acc(N, O.vel(N).diff(t, A) + cross(A.ang_vel_in(N), O.vel(N)))
+
+    # Kinematic differential equations:
+    # Two equalities: one is w_c_n_qd = C.ang_vel_in(N) in three coordinates
+    #                 directions of B, for qd0, qd1 and qd2.
+    #                 the other is v_o_n_qd = O.vel(N) in A.z direction for qd3.
+    # Then, solve for dq/dt's in terms of u's: qd_kd.
+    w_c_n_qd = qd[0]*A.z + qd[1]*B.x + qd[2]*B.y
+    v_o_n_qd = O.pos_from(P).diff(t, A) + cross(A.ang_vel_in(N), O.pos_from(P))
+    kindiffs = Matrix([dot(w_c_n_qd - C.ang_vel_in(N), uv) for uv in B] +
+                      [dot(v_o_n_qd - O.vel(N), A.z)])
+    qd_kd = solve(kindiffs, qd) # noqa:F841
+
+    # Values of generalized speeds during a steady turn for later substitution
+    # into the Fr_star_steady.
+    steady_conditions = solve(kindiffs.subs({qd[1] : 0, qd[3] : 0}), u)
+    steady_conditions.update({qd[1] : 0, qd[3] : 0})
+
+    # Partial angular velocities and velocities.
+    partial_w_C = [C.ang_vel_in(N).diff(ui, N) for ui in u + ua]
+    partial_v_O = [O.vel(N).diff(ui, N) for ui in u + ua]
+    partial_v_P = [P.vel(N).diff(ui, N) for ui in u + ua]
+
+    # Configuration constraint: f_c, the projection of radius r in A.z direction
+    #                                is q[3].
+    # Velocity constraints: f_v, for u3, u4 and u5.
+    # Acceleration constraints: f_a.
+    f_c = Matrix([dot(-r*B.z, A.z) - q[3]])
+    f_v = Matrix([dot(O.vel(N) - (P.vel(N) + cross(C.ang_vel_in(N),
+        O.pos_from(P))), ai).expand() for ai in A])
+    v_o_n = cross(C.ang_vel_in(N), O.pos_from(P))
+    a_o_n = v_o_n.diff(t, A) + cross(A.ang_vel_in(N), v_o_n)
+    f_a = Matrix([dot(O.acc(N) - a_o_n, ai) for ai in A]) # noqa:F841
+
+    # Solve for constraint equations in the form of
+    #                           u_dependent = A_rs * [u_i; u_aux].
+    # First, obtain constraint coefficient matrix:  M_v * [u; ua] = 0;
+    # Second, taking u[0], u[1], u[2] as independent,
+    #         taking u[3], u[4], u[5] as dependent,
+    #         rearranging the matrix of M_v to be A_rs for u_dependent.
+    # Third, u_aux ==0 for u_dep, and resulting dictionary of u_dep_dict.
+    M_v = zeros(3, 9)
+    for i in range(3):
+        for j, ui in enumerate(u + ua):
+            M_v[i, j] = f_v[i].diff(ui)
+
+    M_v_i = M_v[:, :3]
+    M_v_d = M_v[:, 3:6]
+    M_v_aux = M_v[:, 6:]
+    M_v_i_aux = M_v_i.row_join(M_v_aux)
+    A_rs = - M_v_d.inv() * M_v_i_aux
+
+    u_dep = A_rs[:, :3] * Matrix(u[:3])
+    u_dep_dict = dict(zip(u[3:], u_dep))
+
+    # Active forces: F_O acting on point O; F_P acting on point P.
+    # Generalized active forces (unconstrained): Fr_u = F_point * pv_point.
+    F_O = m*g*A.z
+    F_P = Fx * A.x + Fy * A.y + Fz * A.z
+    Fr_u = Matrix([dot(F_O, pv_o) + dot(F_P, pv_p) for pv_o, pv_p in
+            zip(partial_v_O, partial_v_P)])
+
+    # Inertia force: R_star_O.
+    # Inertia of disc: I_C_O, where J is a inertia component about principal axis.
+    # Inertia torque: T_star_C.
+    # Generalized inertia forces (unconstrained): Fr_star_u.
+    R_star_O = -m*O.acc(N)
+    I_C_O = inertia(B, I, J, I)
+    T_star_C = -(dot(I_C_O, C.ang_acc_in(N)) \
+                 + cross(C.ang_vel_in(N), dot(I_C_O, C.ang_vel_in(N))))
+    Fr_star_u = Matrix([dot(R_star_O, pv) + dot(T_star_C, pav) for pv, pav in
+                        zip(partial_v_O, partial_w_C)])
+
+    # Form nonholonomic Fr: Fr_c, and nonholonomic Fr_star: Fr_star_c.
+    # Also, nonholonomic Fr_star in steady turning condition: Fr_star_steady.
+    Fr_c = Fr_u[:3, :].col_join(Fr_u[6:, :]) + A_rs.T * Fr_u[3:6, :]
+    Fr_star_c = Fr_star_u[:3, :].col_join(Fr_star_u[6:, :])\
+                + A_rs.T * Fr_star_u[3:6, :]
+    Fr_star_steady = Fr_star_c.subs(ud_zero).subs(u_dep_dict)\
+            .subs(steady_conditions).subs({q[3]: -r*cos(q[1])}).expand()
+
+
+    # Second, using KaneMethod in mechanics for fr, frstar and frstar_steady.
+
+    # Rigid Bodies: disc, with inertia I_C_O.
+    iner_tuple = (I_C_O, O)
+    disc = RigidBody('disc', O, C, m, iner_tuple)
+    bodyList = [disc]
+
+    # Generalized forces: Gravity: F_o; Auxiliary forces: F_p.
+    F_o = (O, F_O)
+    F_p = (P, F_P)
+    forceList = [F_o,  F_p]
+
+    # KanesMethod.
+    kane = KanesMethod(
+        N, q_ind= q[:3], u_ind= u[:3], kd_eqs=kindiffs,
+        q_dependent=q[3:], configuration_constraints = f_c,
+        u_dependent=u[3:], velocity_constraints= f_v,
+        u_auxiliary=ua
+        )
+
+    # fr, frstar, frstar_steady and kdd(kinematic differential equations).
+    (fr, frstar)= kane.kanes_equations(bodyList, forceList)
+    frstar_steady = frstar.subs(ud_zero).subs(u_dep_dict).subs(steady_conditions)\
+                    .subs({q[3]: -r*cos(q[1])}).expand()
+    kdd = kane.kindiffdict()
+
+    assert Matrix(Fr_c).expand() == fr.expand()
+    assert Matrix(Fr_star_c.subs(kdd)).expand() == frstar.expand()
+    assert (simplify(Matrix(Fr_star_steady).expand()) ==
+            simplify(frstar_steady.expand()))
+
+    syms_in_forcing = find_dynamicsymbols(kane.forcing)
+    for qdi in qd:
+        assert qdi not in syms_in_forcing
+
+
+def test_non_central_inertia():
+    # This tests that the calculation of Fr* does not depend the point
+    # about which the inertia of a rigid body is defined. This test solves
+    # exercises 8.12, 8.17 from Kane 1985.
+
+    # Declare symbols
+    q1, q2, q3 = dynamicsymbols('q1:4')
+    q1d, q2d, q3d = dynamicsymbols('q1:4', level=1)
+    u1, u2, u3, u4, u5 = dynamicsymbols('u1:6')
+    u_prime, R, M, g, e, f, theta = symbols('u\' R, M, g, e, f, theta')
+    a, b, mA, mB, IA, J, K, t = symbols('a b mA mB IA J K t')
+    Q1, Q2, Q3 = symbols('Q1, Q2 Q3')
+    IA22, IA23, IA33 = symbols('IA22 IA23 IA33')
+
+    # Reference Frames
+    F = ReferenceFrame('F')
+    P = F.orientnew('P', 'axis', [-theta, F.y])
+    A = P.orientnew('A', 'axis', [q1, P.x])
+    A.set_ang_vel(F, u1*A.x + u3*A.z)
+    # define frames for wheels
+    B = A.orientnew('B', 'axis', [q2, A.z])
+    C = A.orientnew('C', 'axis', [q3, A.z])
+    B.set_ang_vel(A, u4 * A.z)
+    C.set_ang_vel(A, u5 * A.z)
+
+    # define points D, S*, Q on frame A and their velocities
+    pD = Point('D')
+    pD.set_vel(A, 0)
+    # u3 will not change v_D_F since wheels are still assumed to roll without slip.
+    pD.set_vel(F, u2 * A.y)
+
+    pS_star = pD.locatenew('S*', e*A.y)
+    pQ = pD.locatenew('Q', f*A.y - R*A.x)
+    for p in [pS_star, pQ]:
+        p.v2pt_theory(pD, F, A)
+
+    # masscenters of bodies A, B, C
+    pA_star = pD.locatenew('A*', a*A.y)
+    pB_star = pD.locatenew('B*', b*A.z)
+    pC_star = pD.locatenew('C*', -b*A.z)
+    for p in [pA_star, pB_star, pC_star]:
+        p.v2pt_theory(pD, F, A)
+
+    # points of B, C touching the plane P
+    pB_hat = pB_star.locatenew('B^', -R*A.x)
+    pC_hat = pC_star.locatenew('C^', -R*A.x)
+    pB_hat.v2pt_theory(pB_star, F, B)
+    pC_hat.v2pt_theory(pC_star, F, C)
+
+    # the velocities of B^, C^ are zero since B, C are assumed to roll without slip
+    kde = [q1d - u1, q2d - u4, q3d - u5]
+    vc = [dot(p.vel(F), A.y) for p in [pB_hat, pC_hat]]
+
+    # inertias of bodies A, B, C
+    # IA22, IA23, IA33 are not specified in the problem statement, but are
+    # necessary to define an inertia object. Although the values of
+    # IA22, IA23, IA33 are not known in terms of the variables given in the
+    # problem statement, they do not appear in the general inertia terms.
+    inertia_A = inertia(A, IA, IA22, IA33, 0, IA23, 0)
+    inertia_B = inertia(B, K, K, J)
+    inertia_C = inertia(C, K, K, J)
+
+    # define the rigid bodies A, B, C
+    rbA = RigidBody('rbA', pA_star, A, mA, (inertia_A, pA_star))
+    rbB = RigidBody('rbB', pB_star, B, mB, (inertia_B, pB_star))
+    rbC = RigidBody('rbC', pC_star, C, mB, (inertia_C, pC_star))
+
+    km = KanesMethod(F, q_ind=[q1, q2, q3], u_ind=[u1, u2], kd_eqs=kde,
+                     u_dependent=[u4, u5], velocity_constraints=vc,
+                     u_auxiliary=[u3])
+
+    forces = [(pS_star, -M*g*F.x), (pQ, Q1*A.x + Q2*A.y + Q3*A.z)]
+    bodies = [rbA, rbB, rbC]
+    fr, fr_star = km.kanes_equations(bodies, forces)
+    vc_map = solve(vc, [u4, u5])
+
+    # KanesMethod returns the negative of Fr, Fr* as defined in Kane1985.
+    fr_star_expected = Matrix([
+            -(IA + 2*J*b**2/R**2 + 2*K +
+              mA*a**2 + 2*mB*b**2) * u1.diff(t) - mA*a*u1*u2,
+            -(mA + 2*mB +2*J/R**2) * u2.diff(t) + mA*a*u1**2,
+            0])
+    t = trigsimp(fr_star.subs(vc_map).subs({u3: 0})).doit().expand()
+    assert ((fr_star_expected - t).expand() == zeros(3, 1))
+
+    # define inertias of rigid bodies A, B, C about point D
+    # I_S/O = I_S/S* + I_S*/O
+    bodies2 = []
+    for rb, I_star in zip([rbA, rbB, rbC], [inertia_A, inertia_B, inertia_C]):
+        I = I_star + inertia_of_point_mass(rb.mass,
+                                           rb.masscenter.pos_from(pD),
+                                           rb.frame)
+        bodies2.append(RigidBody('', rb.masscenter, rb.frame, rb.mass,
+                                 (I, pD)))
+    fr2, fr_star2 = km.kanes_equations(bodies2, forces)
+
+    t = trigsimp(fr_star2.subs(vc_map).subs({u3: 0})).doit()
+    assert (fr_star_expected - t).expand() == zeros(3, 1)
+
+def test_sub_qdot():
+    # This test solves exercises 8.12, 8.17 from Kane 1985 and defines
+    # some velocities in terms of q, qdot.
+
+    ## --- Declare symbols ---
+    q1, q2, q3 = dynamicsymbols('q1:4')
+    q1d, q2d, q3d = dynamicsymbols('q1:4', level=1)
+    u1, u2, u3 = dynamicsymbols('u1:4')
+    u_prime, R, M, g, e, f, theta = symbols('u\' R, M, g, e, f, theta')
+    a, b, mA, mB, IA, J, K, t = symbols('a b mA mB IA J K t')
+    IA22, IA23, IA33 = symbols('IA22 IA23 IA33')
+    Q1, Q2, Q3 = symbols('Q1 Q2 Q3')
+
+    # --- Reference Frames ---
+    F = ReferenceFrame('F')
+    P = F.orientnew('P', 'axis', [-theta, F.y])
+    A = P.orientnew('A', 'axis', [q1, P.x])
+    A.set_ang_vel(F, u1*A.x + u3*A.z)
+    # define frames for wheels
+    B = A.orientnew('B', 'axis', [q2, A.z])
+    C = A.orientnew('C', 'axis', [q3, A.z])
+
+    ## --- define points D, S*, Q on frame A and their velocities ---
+    pD = Point('D')
+    pD.set_vel(A, 0)
+    # u3 will not change v_D_F since wheels are still assumed to roll w/o slip
+    pD.set_vel(F, u2 * A.y)
+
+    pS_star = pD.locatenew('S*', e*A.y)
+    pQ = pD.locatenew('Q', f*A.y - R*A.x)
+    # masscenters of bodies A, B, C
+    pA_star = pD.locatenew('A*', a*A.y)
+    pB_star = pD.locatenew('B*', b*A.z)
+    pC_star = pD.locatenew('C*', -b*A.z)
+    for p in [pS_star, pQ, pA_star, pB_star, pC_star]:
+        p.v2pt_theory(pD, F, A)
+
+    # points of B, C touching the plane P
+    pB_hat = pB_star.locatenew('B^', -R*A.x)
+    pC_hat = pC_star.locatenew('C^', -R*A.x)
+    pB_hat.v2pt_theory(pB_star, F, B)
+    pC_hat.v2pt_theory(pC_star, F, C)
+
+    # --- relate qdot, u ---
+    # the velocities of B^, C^ are zero since B, C are assumed to roll w/o slip
+    kde = [dot(p.vel(F), A.y) for p in [pB_hat, pC_hat]]
+    kde += [u1 - q1d]
+    kde_map = solve(kde, [q1d, q2d, q3d])
+    for k, v in list(kde_map.items()):
+        kde_map[k.diff(t)] = v.diff(t)
+
+    # inertias of bodies A, B, C
+    # IA22, IA23, IA33 are not specified in the problem statement, but are
+    # necessary to define an inertia object. Although the values of
+    # IA22, IA23, IA33 are not known in terms of the variables given in the
+    # problem statement, they do not appear in the general inertia terms.
+    inertia_A = inertia(A, IA, IA22, IA33, 0, IA23, 0)
+    inertia_B = inertia(B, K, K, J)
+    inertia_C = inertia(C, K, K, J)
+
+    # define the rigid bodies A, B, C
+    rbA = RigidBody('rbA', pA_star, A, mA, (inertia_A, pA_star))
+    rbB = RigidBody('rbB', pB_star, B, mB, (inertia_B, pB_star))
+    rbC = RigidBody('rbC', pC_star, C, mB, (inertia_C, pC_star))
+
+    ## --- use kanes method ---
+    km = KanesMethod(F, [q1, q2, q3], [u1, u2], kd_eqs=kde, u_auxiliary=[u3])
+
+    forces = [(pS_star, -M*g*F.x), (pQ, Q1*A.x + Q2*A.y + Q3*A.z)]
+    bodies = [rbA, rbB, rbC]
+
+    # Q2 = -u_prime * u2 * Q1 / sqrt(u2**2 + f**2 * u1**2)
+    # -u_prime * R * u2 / sqrt(u2**2 + f**2 * u1**2) = R / Q1 * Q2
+    fr_expected = Matrix([
+            f*Q3 + M*g*e*sin(theta)*cos(q1),
+            Q2 + M*g*sin(theta)*sin(q1),
+            e*M*g*cos(theta) - Q1*f - Q2*R])
+             #Q1 * (f - u_prime * R * u2 / sqrt(u2**2 + f**2 * u1**2)))])
+    fr_star_expected = Matrix([
+            -(IA + 2*J*b**2/R**2 + 2*K +
+              mA*a**2 + 2*mB*b**2) * u1.diff(t) - mA*a*u1*u2,
+            -(mA + 2*mB +2*J/R**2) * u2.diff(t) + mA*a*u1**2,
+            0])
+
+    fr, fr_star = km.kanes_equations(bodies, forces)
+    assert (fr.expand() == fr_expected.expand())
+    assert ((fr_star_expected - trigsimp(fr_star)).expand() == zeros(3, 1))
+
+def test_sub_qdot2():
+    # This test solves exercises 8.3 from Kane 1985 and defines
+    # all velocities in terms of q, qdot. We check that the generalized active
+    # forces are correctly computed if u terms are only defined in the
+    # kinematic differential equations.
+    #
+    # This functionality was added in PR 8948. Without qdot/u substitution, the
+    # KanesMethod constructor will fail during the constraint initialization as
+    # the B matrix will be poorly formed and inversion of the dependent part
+    # will fail.
+
+    g, m, Px, Py, Pz, R, t = symbols('g m Px Py Pz R t')
+    q = dynamicsymbols('q:5')
+    qd = dynamicsymbols('q:5', level=1)
+    u = dynamicsymbols('u:5')
+
+    ## Define inertial, intermediate, and rigid body reference frames
+    A = ReferenceFrame('A')
+    B_prime = A.orientnew('B_prime', 'Axis', [q[0], A.z])
+    B = B_prime.orientnew('B', 'Axis', [pi/2 - q[1], B_prime.x])
+    C = B.orientnew('C', 'Axis', [q[2], B.z])
+
+    ## Define points of interest and their velocities
+    pO = Point('O')
+    pO.set_vel(A, 0)
+
+    # R is the point in plane H that comes into contact with disk C.
+    pR = pO.locatenew('R', q[3]*A.x + q[4]*A.y)
+    pR.set_vel(A, pR.pos_from(pO).diff(t, A))
+    pR.set_vel(B, 0)
+
+    # C^ is the point in disk C that comes into contact with plane H.
+    pC_hat = pR.locatenew('C^', 0)
+    pC_hat.set_vel(C, 0)
+
+    # C* is the point at the center of disk C.
+    pCs = pC_hat.locatenew('C*', R*B.y)
+    pCs.set_vel(C, 0)
+    pCs.set_vel(B, 0)
+
+    # calculate velocites of points C* and C^ in frame A
+    pCs.v2pt_theory(pR, A, B) # points C* and R are fixed in frame B
+    pC_hat.v2pt_theory(pCs, A, C) # points C* and C^ are fixed in frame C
+
+    ## Define forces on each point of the system
+    R_C_hat = Px*A.x + Py*A.y + Pz*A.z
+    R_Cs = -m*g*A.z
+    forces = [(pC_hat, R_C_hat), (pCs, R_Cs)]
+
+    ## Define kinematic differential equations
+    # let ui = omega_C_A & bi (i = 1, 2, 3)
+    # u4 = qd4, u5 = qd5
+    u_expr = [C.ang_vel_in(A) & uv for uv in B]
+    u_expr += qd[3:]
+    kde = [ui - e for ui, e in zip(u, u_expr)]
+    km1 = KanesMethod(A, q, u, kde)
+    fr1, _ = km1.kanes_equations([], forces)
+
+    ## Calculate generalized active forces if we impose the condition that the
+    # disk C is rolling without slipping
+    u_indep = u[:3]
+    u_dep = list(set(u) - set(u_indep))
+    vc = [pC_hat.vel(A) & uv for uv in [A.x, A.y]]
+    km2 = KanesMethod(A, q, u_indep, kde,
+                      u_dependent=u_dep, velocity_constraints=vc)
+    fr2, _ = km2.kanes_equations([], forces)
+
+    fr1_expected = Matrix([
+        -R*g*m*sin(q[1]),
+        -R*(Px*cos(q[0]) + Py*sin(q[0]))*tan(q[1]),
+        R*(Px*cos(q[0]) + Py*sin(q[0])),
+        Px,
+        Py])
+    fr2_expected = Matrix([
+        -R*g*m*sin(q[1]),
+        0,
+        0])
+    assert (trigsimp(fr1.expand()) == trigsimp(fr1_expected.expand()))
+    assert (trigsimp(fr2.expand()) == trigsimp(fr2_expected.expand()))

venv/lib/python3.10/site-packages/sympy/physics/mechanics/tests/test_kane3.py

@@ -0,0 +1,293 @@
+from sympy.core.evalf import evalf
+from sympy.core.numbers import pi
+from sympy.core.symbol import symbols
+from sympy.functions.elementary.miscellaneous import sqrt
+from sympy.functions.elementary.trigonometric import acos, sin, cos
+from sympy.matrices.dense import Matrix
+from sympy.physics.mechanics import (ReferenceFrame, dynamicsymbols,
+    KanesMethod, inertia, msubs, Point, RigidBody, dot)
+from sympy.testing.pytest import slow, ON_CI, skip
+
+
+@slow
+def test_bicycle():
+    if ON_CI:
+        skip("Too slow for CI.")
+    # Code to get equations of motion for a bicycle modeled as in:
+    # J.P Meijaard, Jim M Papadopoulos, Andy Ruina and A.L Schwab. Linearized
+    # dynamics equations for the balance and steer of a bicycle: a benchmark
+    # and review. Proceedings of The Royal Society (2007) 463, 1955-1982
+    # doi: 10.1098/rspa.2007.1857
+
+    # Note that this code has been crudely ported from Autolev, which is the
+    # reason for some of the unusual naming conventions. It was purposefully as
+    # similar as possible in order to aide debugging.
+
+    # Declare Coordinates & Speeds
+    # Simple definitions for qdots - qd = u
+    # Speeds are: yaw frame ang. rate, roll frame ang. rate, rear wheel frame
+    # ang.  rate (spinning motion), frame ang. rate (pitching motion), steering
+    # frame ang. rate, and front wheel ang. rate (spinning motion).
+    # Wheel positions are ignorable coordinates, so they are not introduced.
+    q1, q2, q4, q5 = dynamicsymbols('q1 q2 q4 q5')
+    q1d, q2d, q4d, q5d = dynamicsymbols('q1 q2 q4 q5', 1)
+    u1, u2, u3, u4, u5, u6 = dynamicsymbols('u1 u2 u3 u4 u5 u6')
+    u1d, u2d, u3d, u4d, u5d, u6d = dynamicsymbols('u1 u2 u3 u4 u5 u6', 1)
+
+    # Declare System's Parameters
+    WFrad, WRrad, htangle, forkoffset = symbols('WFrad WRrad htangle forkoffset')
+    forklength, framelength, forkcg1 = symbols('forklength framelength forkcg1')
+    forkcg3, framecg1, framecg3, Iwr11 = symbols('forkcg3 framecg1 framecg3 Iwr11')
+    Iwr22, Iwf11, Iwf22, Iframe11 = symbols('Iwr22 Iwf11 Iwf22 Iframe11')
+    Iframe22, Iframe33, Iframe31, Ifork11 = symbols('Iframe22 Iframe33 Iframe31 Ifork11')
+    Ifork22, Ifork33, Ifork31, g = symbols('Ifork22 Ifork33 Ifork31 g')
+    mframe, mfork, mwf, mwr = symbols('mframe mfork mwf mwr')
+
+    # Set up reference frames for the system
+    # N - inertial
+    # Y - yaw
+    # R - roll
+    # WR - rear wheel, rotation angle is ignorable coordinate so not oriented
+    # Frame - bicycle frame
+    # TempFrame - statically rotated frame for easier reference inertia definition
+    # Fork - bicycle fork
+    # TempFork - statically rotated frame for easier reference inertia definition
+    # WF - front wheel, again posses a ignorable coordinate
+    N = ReferenceFrame('N')
+    Y = N.orientnew('Y', 'Axis', [q1, N.z])
+    R = Y.orientnew('R', 'Axis', [q2, Y.x])
+    Frame = R.orientnew('Frame', 'Axis', [q4 + htangle, R.y])
+    WR = ReferenceFrame('WR')
+    TempFrame = Frame.orientnew('TempFrame', 'Axis', [-htangle, Frame.y])
+    Fork = Frame.orientnew('Fork', 'Axis', [q5, Frame.x])
+    TempFork = Fork.orientnew('TempFork', 'Axis', [-htangle, Fork.y])
+    WF = ReferenceFrame('WF')
+
+    # Kinematics of the Bicycle First block of code is forming the positions of
+    # the relevant points
+    # rear wheel contact -> rear wheel mass center -> frame mass center +
+    # frame/fork connection -> fork mass center + front wheel mass center ->
+    # front wheel contact point
+    WR_cont = Point('WR_cont')
+    WR_mc = WR_cont.locatenew('WR_mc', WRrad * R.z)
+    Steer = WR_mc.locatenew('Steer', framelength * Frame.z)
+    Frame_mc = WR_mc.locatenew('Frame_mc', - framecg1 * Frame.x
+                                           + framecg3 * Frame.z)
+    Fork_mc = Steer.locatenew('Fork_mc', - forkcg1 * Fork.x
+                                         + forkcg3 * Fork.z)
+    WF_mc = Steer.locatenew('WF_mc', forklength * Fork.x + forkoffset * Fork.z)
+    WF_cont = WF_mc.locatenew('WF_cont', WFrad * (dot(Fork.y, Y.z) * Fork.y -
+                                                  Y.z).normalize())
+
+    # Set the angular velocity of each frame.
+    # Angular accelerations end up being calculated automatically by
+    # differentiating the angular velocities when first needed.
+    # u1 is yaw rate
+    # u2 is roll rate
+    # u3 is rear wheel rate
+    # u4 is frame pitch rate
+    # u5 is fork steer rate
+    # u6 is front wheel rate
+    Y.set_ang_vel(N, u1 * Y.z)
+    R.set_ang_vel(Y, u2 * R.x)
+    WR.set_ang_vel(Frame, u3 * Frame.y)
+    Frame.set_ang_vel(R, u4 * Frame.y)
+    Fork.set_ang_vel(Frame, u5 * Fork.x)
+    WF.set_ang_vel(Fork, u6 * Fork.y)
+
+    # Form the velocities of the previously defined points, using the 2 - point
+    # theorem (written out by hand here).  Accelerations again are calculated
+    # automatically when first needed.
+    WR_cont.set_vel(N, 0)
+    WR_mc.v2pt_theory(WR_cont, N, WR)
+    Steer.v2pt_theory(WR_mc, N, Frame)
+    Frame_mc.v2pt_theory(WR_mc, N, Frame)
+    Fork_mc.v2pt_theory(Steer, N, Fork)
+    WF_mc.v2pt_theory(Steer, N, Fork)
+    WF_cont.v2pt_theory(WF_mc, N, WF)
+
+    # Sets the inertias of each body. Uses the inertia frame to construct the
+    # inertia dyadics. Wheel inertias are only defined by principle moments of
+    # inertia, and are in fact constant in the frame and fork reference frames;
+    # it is for this reason that the orientations of the wheels does not need
+    # to be defined. The frame and fork inertias are defined in the 'Temp'
+    # frames which are fixed to the appropriate body frames; this is to allow
+    # easier input of the reference values of the benchmark paper. Note that
+    # due to slightly different orientations, the products of inertia need to
+    # have their signs flipped; this is done later when entering the numerical
+    # value.
+
+    Frame_I = (inertia(TempFrame, Iframe11, Iframe22, Iframe33, 0, 0, Iframe31), Frame_mc)
+    Fork_I = (inertia(TempFork, Ifork11, Ifork22, Ifork33, 0, 0, Ifork31), Fork_mc)
+    WR_I = (inertia(Frame, Iwr11, Iwr22, Iwr11), WR_mc)
+    WF_I = (inertia(Fork, Iwf11, Iwf22, Iwf11), WF_mc)
+
+    # Declaration of the RigidBody containers. ::
+
+    BodyFrame = RigidBody('BodyFrame', Frame_mc, Frame, mframe, Frame_I)
+    BodyFork = RigidBody('BodyFork', Fork_mc, Fork, mfork, Fork_I)
+    BodyWR = RigidBody('BodyWR', WR_mc, WR, mwr, WR_I)
+    BodyWF = RigidBody('BodyWF', WF_mc, WF, mwf, WF_I)
+
+    # The kinematic differential equations; they are defined quite simply. Each
+    # entry in this list is equal to zero.
+    kd = [q1d - u1, q2d - u2, q4d - u4, q5d - u5]
+
+    # The nonholonomic constraints are the velocity of the front wheel contact
+    # point dotted into the X, Y, and Z directions; the yaw frame is used as it
+    # is "closer" to the front wheel (1 less DCM connecting them). These
+    # constraints force the velocity of the front wheel contact point to be 0
+    # in the inertial frame; the X and Y direction constraints enforce a
+    # "no-slip" condition, and the Z direction constraint forces the front
+    # wheel contact point to not move away from the ground frame, essentially
+    # replicating the holonomic constraint which does not allow the frame pitch
+    # to change in an invalid fashion.
+
+    conlist_speed = [WF_cont.vel(N) & Y.x, WF_cont.vel(N) & Y.y, WF_cont.vel(N) & Y.z]
+
+    # The holonomic constraint is that the position from the rear wheel contact
+    # point to the front wheel contact point when dotted into the
+    # normal-to-ground plane direction must be zero; effectively that the front
+    # and rear wheel contact points are always touching the ground plane. This
+    # is actually not part of the dynamic equations, but instead is necessary
+    # for the lineraization process.
+
+    conlist_coord = [WF_cont.pos_from(WR_cont) & Y.z]
+
+    # The force list; each body has the appropriate gravitational force applied
+    # at its mass center.
+    FL = [(Frame_mc, -mframe * g * Y.z),
+        (Fork_mc, -mfork * g * Y.z),
+        (WF_mc, -mwf * g * Y.z),
+        (WR_mc, -mwr * g * Y.z)]
+    BL = [BodyFrame, BodyFork, BodyWR, BodyWF]
+
+
+    # The N frame is the inertial frame, coordinates are supplied in the order
+    # of independent, dependent coordinates, as are the speeds. The kinematic
+    # differential equation are also entered here.  Here the dependent speeds
+    # are specified, in the same order they were provided in earlier, along
+    # with the non-holonomic constraints.  The dependent coordinate is also
+    # provided, with the holonomic constraint.  Again, this is only provided
+    # for the linearization process.
+
+    KM = KanesMethod(N, q_ind=[q1, q2, q5],
+            q_dependent=[q4], configuration_constraints=conlist_coord,
+            u_ind=[u2, u3, u5],
+            u_dependent=[u1, u4, u6], velocity_constraints=conlist_speed,
+            kd_eqs=kd)
+    (fr, frstar) = KM.kanes_equations(BL, FL)
+
+    # This is the start of entering in the numerical values from the benchmark
+    # paper to validate the eigen values of the linearized equations from this
+    # model to the reference eigen values. Look at the aforementioned paper for
+    # more information. Some of these are intermediate values, used to
+    # transform values from the paper into the coordinate systems used in this
+    # model.
+    PaperRadRear                    =  0.3
+    PaperRadFront                   =  0.35
+    HTA                             =  evalf.N(pi / 2 - pi / 10)
+    TrailPaper                      =  0.08
+    rake                            =  evalf.N(-(TrailPaper*sin(HTA)-(PaperRadFront*cos(HTA))))
+    PaperWb                         =  1.02
+    PaperFrameCgX                   =  0.3
+    PaperFrameCgZ                   =  0.9
+    PaperForkCgX                    =  0.9
+    PaperForkCgZ                    =  0.7
+    FrameLength                     =  evalf.N(PaperWb*sin(HTA)-(rake-(PaperRadFront-PaperRadRear)*cos(HTA)))
+    FrameCGNorm                     =  evalf.N((PaperFrameCgZ - PaperRadRear-(PaperFrameCgX/sin(HTA))*cos(HTA))*sin(HTA))
+    FrameCGPar                      =  evalf.N(PaperFrameCgX / sin(HTA) + (PaperFrameCgZ - PaperRadRear - PaperFrameCgX / sin(HTA) * cos(HTA)) * cos(HTA))
+    tempa                           =  evalf.N(PaperForkCgZ - PaperRadFront)
+    tempb                           =  evalf.N(PaperWb-PaperForkCgX)
+    tempc                           =  evalf.N(sqrt(tempa**2+tempb**2))
+    PaperForkL                      =  evalf.N(PaperWb*cos(HTA)-(PaperRadFront-PaperRadRear)*sin(HTA))
+    ForkCGNorm                      =  evalf.N(rake+(tempc * sin(pi/2-HTA-acos(tempa/tempc))))
+    ForkCGPar                       =  evalf.N(tempc * cos((pi/2-HTA)-acos(tempa/tempc))-PaperForkL)
+
+    # Here is the final assembly of the numerical values. The symbol 'v' is the
+    # forward speed of the bicycle (a concept which only makes sense in the
+    # upright, static equilibrium case?). These are in a dictionary which will
+    # later be substituted in. Again the sign on the *product* of inertia
+    # values is flipped here, due to different orientations of coordinate
+    # systems.
+    v = symbols('v')
+    val_dict = {WFrad: PaperRadFront,
+                WRrad: PaperRadRear,
+                htangle: HTA,
+                forkoffset: rake,
+                forklength: PaperForkL,
+                framelength: FrameLength,
+                forkcg1: ForkCGPar,
+                forkcg3: ForkCGNorm,
+                framecg1: FrameCGNorm,
+                framecg3: FrameCGPar,
+                Iwr11: 0.0603,
+                Iwr22: 0.12,
+                Iwf11: 0.1405,
+                Iwf22: 0.28,
+                Ifork11: 0.05892,
+                Ifork22: 0.06,
+                Ifork33: 0.00708,
+                Ifork31: 0.00756,
+                Iframe11: 9.2,
+                Iframe22: 11,
+                Iframe33: 2.8,
+                Iframe31: -2.4,
+                mfork: 4,
+                mframe: 85,
+                mwf: 3,
+                mwr: 2,
+                g: 9.81,
+                q1: 0,
+                q2: 0,
+                q4: 0,
+                q5: 0,
+                u1: 0,
+                u2: 0,
+                u3: v / PaperRadRear,
+                u4: 0,
+                u5: 0,
+                u6: v / PaperRadFront}
+
+    # Linearizes the forcing vector; the equations are set up as MM udot =
+    # forcing, where MM is the mass matrix, udot is the vector representing the
+    # time derivatives of the generalized speeds, and forcing is a vector which
+    # contains both external forcing terms and internal forcing terms, such as
+    # centripital or coriolis forces.  This actually returns a matrix with as
+    # many rows as *total* coordinates and speeds, but only as many columns as
+    # independent coordinates and speeds.
+
+    forcing_lin = KM.linearize()[0]
+
+    # As mentioned above, the size of the linearized forcing terms is expanded
+    # to include both q's and u's, so the mass matrix must have this done as
+    # well.  This will likely be changed to be part of the linearized process,
+    # for future reference.
+    MM_full = KM.mass_matrix_full
+
+    MM_full_s = msubs(MM_full, val_dict)
+    forcing_lin_s = msubs(forcing_lin, KM.kindiffdict(), val_dict)
+
+    MM_full_s = MM_full_s.evalf()
+    forcing_lin_s = forcing_lin_s.evalf()
+
+    # Finally, we construct an "A" matrix for the form xdot = A x (x being the
+    # state vector, although in this case, the sizes are a little off). The
+    # following line extracts only the minimum entries required for eigenvalue
+    # analysis, which correspond to rows and columns for lean, steer, lean
+    # rate, and steer rate.
+    Amat = MM_full_s.inv() * forcing_lin_s
+    A = Amat.extract([1, 2, 4, 6], [1, 2, 3, 5])
+
+    # Precomputed for comparison
+    Res = Matrix([[               0,                                           0,                  1.0,                    0],
+                  [               0,                                           0,                    0,                  1.0],
+                  [9.48977444677355, -0.891197738059089*v**2 - 0.571523173729245, -0.105522449805691*v, -0.330515398992311*v],
+                  [11.7194768719633,   -1.97171508499972*v**2 + 30.9087533932407,   3.67680523332152*v,  -3.08486552743311*v]])
+
+
+    # Actual eigenvalue comparison
+    eps = 1.e-12
+    for i in range(6):
+        error = Res.subs(v, i) - A.subs(v, i)
+        assert all(abs(x) < eps for x in error)

venv/lib/python3.10/site-packages/sympy/physics/mechanics/tests/test_kane4.py

@@ -0,0 +1,115 @@
+from sympy.core.backend import (cos, sin, Matrix, symbols)
+from sympy.physics.mechanics import (dynamicsymbols, ReferenceFrame, Point,
+                                        KanesMethod, Particle)
+
+def test_replace_qdots_in_force():
+    # Test PR 16700 "Replaces qdots with us in force-list in kanes.py"
+    # The new functionality allows one to specify forces in qdots which will
+    # automatically be replaced with u:s which are defined by the kde supplied
+    # to KanesMethod. The test case is the double pendulum with interacting
+    # forces in the example of chapter 4.7 "CONTRIBUTING INTERACTION FORCES"
+    # in Ref. [1]. Reference list at end test function.
+
+    q1, q2 = dynamicsymbols('q1, q2')
+    qd1, qd2 = dynamicsymbols('q1, q2', level=1)
+    u1, u2 = dynamicsymbols('u1, u2')
+
+    l, m = symbols('l, m')
+
+    N = ReferenceFrame('N') # Inertial frame
+    A = N.orientnew('A', 'Axis', (q1, N.z)) # Rod A frame
+    B = A.orientnew('B', 'Axis', (q2, N.z)) # Rod B frame
+
+    O = Point('O') # Origo
+    O.set_vel(N, 0)
+
+    P = O.locatenew('P', ( l * A.x )) # Point @ end of rod A
+    P.v2pt_theory(O, N, A)
+
+    Q = P.locatenew('Q', ( l * B.x )) # Point @ end of rod B
+    Q.v2pt_theory(P, N, B)
+
+    Ap = Particle('Ap', P, m)
+    Bp = Particle('Bp', Q, m)
+
+    # The forces are specified below. sigma is the torsional spring stiffness
+    # and delta is the viscous damping coefficient acting between the two
+    # bodies. Here, we specify the viscous damper as function of qdots prior
+    # forming the kde. In more complex systems it not might be obvious which
+    # kde is most efficient, why it is convenient to specify viscous forces in
+    # qdots independently of the kde.
+    sig, delta = symbols('sigma, delta')
+    Ta = (sig * q2 + delta * qd2) * N.z
+    forces = [(A, Ta), (B, -Ta)]
+
+    # Try different kdes.
+    kde1 = [u1 - qd1, u2 - qd2]
+    kde2 = [u1 - qd1, u2 - (qd1 + qd2)]
+
+    KM1 = KanesMethod(N, [q1, q2], [u1, u2], kd_eqs=kde1)
+    fr1, fstar1 = KM1.kanes_equations([Ap, Bp], forces)
+
+    KM2 = KanesMethod(N, [q1, q2], [u1, u2], kd_eqs=kde2)
+    fr2, fstar2 = KM2.kanes_equations([Ap, Bp], forces)
+
+    # Check EOM for KM2:
+    # Mass and force matrix from p.6 in Ref. [2] with added forces from
+    # example of chapter 4.7 in [1] and without gravity.
+    forcing_matrix_expected = Matrix( [ [ m * l**2 * sin(q2) * u2**2 + sig * q2
+                                        + delta * (u2 - u1)],
+                                        [ m * l**2 * sin(q2) * -u1**2 - sig * q2
+                                        - delta * (u2 - u1)] ] )
+    mass_matrix_expected = Matrix( [ [ 2 * m * l**2, m * l**2 * cos(q2) ],
+                                    [ m * l**2 * cos(q2), m * l**2 ] ] )
+
+    assert (KM2.mass_matrix.expand() == mass_matrix_expected.expand())
+    assert (KM2.forcing.expand() == forcing_matrix_expected.expand())
+
+    # Check fr1 with reference fr_expected from [1] with u:s instead of qdots.
+    fr1_expected = Matrix([ 0, -(sig*q2 + delta * u2) ])
+    assert fr1.expand() == fr1_expected.expand()
+
+    # Check fr2
+    fr2_expected = Matrix([sig * q2 + delta * (u2 - u1),
+                            - sig * q2 - delta * (u2 - u1)])
+    assert fr2.expand() == fr2_expected.expand()
+
+    # Specifying forces in u:s should stay the same:
+    Ta = (sig * q2 + delta * u2) * N.z
+    forces = [(A, Ta), (B, -Ta)]
+    KM1 = KanesMethod(N, [q1, q2], [u1, u2], kd_eqs=kde1)
+    fr1, fstar1 = KM1.kanes_equations([Ap, Bp], forces)
+
+    assert fr1.expand() == fr1_expected.expand()
+
+    Ta = (sig * q2 + delta * (u2-u1)) * N.z
+    forces = [(A, Ta), (B, -Ta)]
+    KM2 = KanesMethod(N, [q1, q2], [u1, u2], kd_eqs=kde2)
+    fr2, fstar2 = KM2.kanes_equations([Ap, Bp], forces)
+
+    assert fr2.expand() == fr2_expected.expand()
+
+    # Test if we have a qubic qdot force:
+    Ta = (sig * q2 + delta * qd2**3) * N.z
+    forces = [(A, Ta), (B, -Ta)]
+
+    KM1 = KanesMethod(N, [q1, q2], [u1, u2], kd_eqs=kde1)
+    fr1, fstar1 = KM1.kanes_equations([Ap, Bp], forces)
+
+    fr1_cubic_expected = Matrix([ 0, -(sig*q2 + delta * u2**3) ])
+
+    assert fr1.expand() == fr1_cubic_expected.expand()
+
+    KM2 = KanesMethod(N, [q1, q2], [u1, u2], kd_eqs=kde2)
+    fr2, fstar2 = KM2.kanes_equations([Ap, Bp], forces)
+
+    fr2_cubic_expected = Matrix([sig * q2 + delta * (u2 - u1)**3,
+                            - sig * q2 - delta * (u2 - u1)**3])
+
+    assert fr2.expand() == fr2_cubic_expected.expand()
+
+    # References:
+    # [1] T.R. Kane, D. a Levinson, Dynamics Theory and Applications, 2005.
+    # [2] Arun K Banerjee, Flexible Multibody Dynamics:Efficient Formulations
+    #     and Applications, John Wiley and Sons, Ltd, 2016.
+    #     doi:http://dx.doi.org/10.1002/9781119015635.

venv/lib/python3.10/site-packages/sympy/physics/mechanics/tests/test_lagrange.py

@@ -0,0 +1,247 @@
+from sympy.physics.mechanics import (dynamicsymbols, ReferenceFrame, Point,
+                                    RigidBody, LagrangesMethod, Particle,
+                                    inertia, Lagrangian)
+from sympy.core.function import (Derivative, Function)
+from sympy.core.numbers import pi
+from sympy.core.symbol import symbols
+from sympy.functions.elementary.trigonometric import (cos, sin, tan)
+from sympy.matrices.dense import Matrix
+from sympy.simplify.simplify import simplify
+from sympy.testing.pytest import raises
+
+
+def test_invalid_coordinates():
+    # Simple pendulum, but use symbol instead of dynamicsymbol
+    l, m, g = symbols('l m g')
+    q = symbols('q')  # Generalized coordinate
+    N, O = ReferenceFrame('N'), Point('O')
+    O.set_vel(N, 0)
+    P = Particle('P', Point('P'), m)
+    P.point.set_pos(O, l * (sin(q) * N.x - cos(q) * N.y))
+    P.potential_energy = m * g * P.point.pos_from(O).dot(N.y)
+    L = Lagrangian(N, P)
+    raises(ValueError, lambda: LagrangesMethod(L, [q], bodies=P))
+
+
+def test_disc_on_an_incline_plane():
+    # Disc rolling on an inclined plane
+    # First the generalized coordinates are created. The mass center of the
+    # disc is located from top vertex of the inclined plane by the generalized
+    # coordinate 'y'. The orientation of the disc is defined by the angle
+    # 'theta'. The mass of the disc is 'm' and its radius is 'R'. The length of
+    # the inclined path is 'l', the angle of inclination is 'alpha'. 'g' is the
+    # gravitational constant.
+    y, theta = dynamicsymbols('y theta')
+    yd, thetad = dynamicsymbols('y theta', 1)
+    m, g, R, l, alpha = symbols('m g R l alpha')
+
+    # Next, we create the inertial reference frame 'N'. A reference frame 'A'
+    # is attached to the inclined plane. Finally a frame is created which is attached to the disk.
+    N = ReferenceFrame('N')
+    A = N.orientnew('A', 'Axis', [pi/2 - alpha, N.z])
+    B = A.orientnew('B', 'Axis', [-theta, A.z])
+
+    # Creating the disc 'D'; we create the point that represents the mass
+    # center of the disc and set its velocity. The inertia dyadic of the disc
+    # is created. Finally, we create the disc.
+    Do = Point('Do')
+    Do.set_vel(N, yd * A.x)
+    I = m * R**2/2 * B.z | B.z
+    D = RigidBody('D', Do, B, m, (I, Do))
+
+    # To construct the Lagrangian, 'L', of the disc, we determine its kinetic
+    # and potential energies, T and U, respectively. L is defined as the
+    # difference between T and U.
+    D.potential_energy = m * g * (l - y) * sin(alpha)
+    L = Lagrangian(N, D)
+
+    # We then create the list of generalized coordinates and constraint
+    # equations. The constraint arises due to the disc rolling without slip on
+    # on the inclined path. We then invoke the 'LagrangesMethod' class and
+    # supply it the necessary arguments and generate the equations of motion.
+    # The'rhs' method solves for the q_double_dots (i.e. the second derivative
+    # with respect to time  of the generalized coordinates and the lagrange
+    # multipliers.
+    q = [y, theta]
+    hol_coneqs = [y - R * theta]
+    m = LagrangesMethod(L, q, hol_coneqs=hol_coneqs)
+    m.form_lagranges_equations()
+    rhs = m.rhs()
+    rhs.simplify()
+    assert rhs[2] == 2*g*sin(alpha)/3
+
+
+def test_simp_pen():
+    # This tests that the equations generated by LagrangesMethod are identical
+    # to those obtained by hand calculations. The system under consideration is
+    # the simple pendulum.
+    # We begin by creating the generalized coordinates as per the requirements
+    # of LagrangesMethod. Also we created the associate symbols
+    # that characterize the system: 'm' is the mass of the bob, l is the length
+    # of the massless rigid rod connecting the bob to a point O fixed in the
+    # inertial frame.
+    q, u = dynamicsymbols('q u')
+    qd, ud = dynamicsymbols('q u ', 1)
+    l, m, g = symbols('l m g')
+
+    # We then create the inertial frame and a frame attached to the massless
+    # string following which we define the inertial angular velocity of the
+    # string.
+    N = ReferenceFrame('N')
+    A = N.orientnew('A', 'Axis', [q, N.z])
+    A.set_ang_vel(N, qd * N.z)
+
+    # Next, we create the point O and fix it in the inertial frame. We then
+    # locate the point P to which the bob is attached. Its corresponding
+    # velocity is then determined by the 'two point formula'.
+    O = Point('O')
+    O.set_vel(N, 0)
+    P = O.locatenew('P', l * A.x)
+    P.v2pt_theory(O, N, A)
+
+    # The 'Particle' which represents the bob is then created and its
+    # Lagrangian generated.
+    Pa = Particle('Pa', P, m)
+    Pa.potential_energy = - m * g * l * cos(q)
+    L = Lagrangian(N, Pa)
+
+    # The 'LagrangesMethod' class is invoked to obtain equations of motion.
+    lm = LagrangesMethod(L, [q])
+    lm.form_lagranges_equations()
+    RHS = lm.rhs()
+    assert RHS[1] == -g*sin(q)/l
+
+
+def test_nonminimal_pendulum():
+    q1, q2 = dynamicsymbols('q1:3')
+    q1d, q2d = dynamicsymbols('q1:3', level=1)
+    L, m, t = symbols('L, m, t')
+    g = 9.8
+    # Compose World Frame
+    N = ReferenceFrame('N')
+    pN = Point('N*')
+    pN.set_vel(N, 0)
+    # Create point P, the pendulum mass
+    P = pN.locatenew('P1', q1*N.x + q2*N.y)
+    P.set_vel(N, P.pos_from(pN).dt(N))
+    pP = Particle('pP', P, m)
+    # Constraint Equations
+    f_c = Matrix([q1**2 + q2**2 - L**2])
+    # Calculate the lagrangian, and form the equations of motion
+    Lag = Lagrangian(N, pP)
+    LM = LagrangesMethod(Lag, [q1, q2], hol_coneqs=f_c,
+            forcelist=[(P, m*g*N.x)], frame=N)
+    LM.form_lagranges_equations()
+    # Check solution
+    lam1 = LM.lam_vec[0, 0]
+    eom_sol = Matrix([[m*Derivative(q1, t, t) - 9.8*m + 2*lam1*q1],
+                      [m*Derivative(q2, t, t) + 2*lam1*q2]])
+    assert LM.eom == eom_sol
+    # Check multiplier solution
+    lam_sol = Matrix([(19.6*q1 + 2*q1d**2 + 2*q2d**2)/(4*q1**2/m + 4*q2**2/m)])
+    assert simplify(LM.solve_multipliers(sol_type='Matrix')) == simplify(lam_sol)
+
+
+def test_dub_pen():
+
+    # The system considered is the double pendulum. Like in the
+    # test of the simple pendulum above, we begin by creating the generalized
+    # coordinates and the simple generalized speeds and accelerations which
+    # will be used later. Following this we create frames and points necessary
+    # for the kinematics. The procedure isn't explicitly explained as this is
+    # similar to the simple  pendulum. Also this is documented on the pydy.org
+    # website.
+    q1, q2 = dynamicsymbols('q1 q2')
+    q1d, q2d = dynamicsymbols('q1 q2', 1)
+    q1dd, q2dd = dynamicsymbols('q1 q2', 2)
+    u1, u2 = dynamicsymbols('u1 u2')
+    u1d, u2d = dynamicsymbols('u1 u2', 1)
+    l, m, g = symbols('l m g')
+
+    N = ReferenceFrame('N')
+    A = N.orientnew('A', 'Axis', [q1, N.z])
+    B = N.orientnew('B', 'Axis', [q2, N.z])
+
+    A.set_ang_vel(N, q1d * A.z)
+    B.set_ang_vel(N, q2d * A.z)
+
+    O = Point('O')
+    P = O.locatenew('P', l * A.x)
+    R = P.locatenew('R', l * B.x)
+
+    O.set_vel(N, 0)
+    P.v2pt_theory(O, N, A)
+    R.v2pt_theory(P, N, B)
+
+    ParP = Particle('ParP', P, m)
+    ParR = Particle('ParR', R, m)
+
+    ParP.potential_energy = - m * g * l * cos(q1)
+    ParR.potential_energy = - m * g * l * cos(q1) - m * g * l * cos(q2)
+    L = Lagrangian(N, ParP, ParR)
+    lm = LagrangesMethod(L, [q1, q2], bodies=[ParP, ParR])
+    lm.form_lagranges_equations()
+
+    assert simplify(l*m*(2*g*sin(q1) + l*sin(q1)*sin(q2)*q2dd
+        + l*sin(q1)*cos(q2)*q2d**2 - l*sin(q2)*cos(q1)*q2d**2
+        + l*cos(q1)*cos(q2)*q2dd + 2*l*q1dd) - lm.eom[0]) == 0
+    assert simplify(l*m*(g*sin(q2) + l*sin(q1)*sin(q2)*q1dd
+        - l*sin(q1)*cos(q2)*q1d**2 + l*sin(q2)*cos(q1)*q1d**2
+        + l*cos(q1)*cos(q2)*q1dd + l*q2dd) - lm.eom[1]) == 0
+    assert lm.bodies == [ParP, ParR]
+
+
+def test_rolling_disc():
+    # Rolling Disc Example
+    # Here the rolling disc is formed from the contact point up, removing the
+    # need to introduce generalized speeds. Only 3 configuration and 3
+    # speed variables are need to describe this system, along with the
+    # disc's mass and radius, and the local gravity.
+    q1, q2, q3 = dynamicsymbols('q1 q2 q3')
+    q1d, q2d, q3d = dynamicsymbols('q1 q2 q3', 1)
+    r, m, g = symbols('r m g')
+
+    # The kinematics are formed by a series of simple rotations. Each simple
+    # rotation creates a new frame, and the next rotation is defined by the new
+    # frame's basis vectors. This example uses a 3-1-2 series of rotations, or
+    # Z, X, Y series of rotations. Angular velocity for this is defined using
+    # the second frame's basis (the lean frame).
+    N = ReferenceFrame('N')
+    Y = N.orientnew('Y', 'Axis', [q1, N.z])
+    L = Y.orientnew('L', 'Axis', [q2, Y.x])
+    R = L.orientnew('R', 'Axis', [q3, L.y])
+
+    # This is the translational kinematics. We create a point with no velocity
+    # in N; this is the contact point between the disc and ground. Next we form
+    # the position vector from the contact point to the disc's center of mass.
+    # Finally we form the velocity and acceleration of the disc.
+    C = Point('C')
+    C.set_vel(N, 0)
+    Dmc = C.locatenew('Dmc', r * L.z)
+    Dmc.v2pt_theory(C, N, R)
+
+    # Forming the inertia dyadic.
+    I = inertia(L, m/4 * r**2, m/2 * r**2, m/4 * r**2)
+    BodyD = RigidBody('BodyD', Dmc, R, m, (I, Dmc))
+
+    # Finally we form the equations of motion, using the same steps we did
+    # before. Supply the Lagrangian, the generalized speeds.
+    BodyD.potential_energy = - m * g * r * cos(q2)
+    Lag = Lagrangian(N, BodyD)
+    q = [q1, q2, q3]
+    q1 = Function('q1')
+    q2 = Function('q2')
+    q3 = Function('q3')
+    l = LagrangesMethod(Lag, q)
+    l.form_lagranges_equations()
+    RHS = l.rhs()
+    RHS.simplify()
+    t = symbols('t')
+
+    assert (l.mass_matrix[3:6] == [0, 5*m*r**2/4, 0])
+    assert RHS[4].simplify() == (
+        (-8*g*sin(q2(t)) + r*(5*sin(2*q2(t))*Derivative(q1(t), t) +
+        12*cos(q2(t))*Derivative(q3(t), t))*Derivative(q1(t), t))/(10*r))
+    assert RHS[5] == (-5*cos(q2(t))*Derivative(q1(t), t) + 6*tan(q2(t)
+        )*Derivative(q3(t), t) + 4*Derivative(q1(t), t)/cos(q2(t))
+        )*Derivative(q2(t), t)

venv/lib/python3.10/site-packages/sympy/physics/mechanics/tests/test_lagrange2.py

@@ -0,0 +1,46 @@
+from sympy.core.backend import symbols
+from sympy.physics.mechanics import dynamicsymbols
+from sympy.physics.mechanics import ReferenceFrame, Point, Particle
+from sympy.physics.mechanics import LagrangesMethod, Lagrangian
+
+### This test asserts that a system with more than one external forces
+### is acurately formed with Lagrange method (see issue #8626)
+
+def test_lagrange_2forces():
+    ### Equations for two damped springs in serie with two forces
+
+    ### generalized coordinates
+    q1, q2 = dynamicsymbols('q1, q2')
+    ### generalized speeds
+    q1d, q2d = dynamicsymbols('q1, q2', 1)
+
+    ### Mass, spring strength, friction coefficient
+    m, k, nu = symbols('m, k, nu')
+
+    N = ReferenceFrame('N')
+    O = Point('O')
+
+    ### Two points
+    P1 = O.locatenew('P1', q1 * N.x)
+    P1.set_vel(N, q1d * N.x)
+    P2 = O.locatenew('P1', q2 * N.x)
+    P2.set_vel(N, q2d * N.x)
+
+    pP1 = Particle('pP1', P1, m)
+    pP1.potential_energy = k * q1**2 / 2
+
+    pP2 = Particle('pP2', P2, m)
+    pP2.potential_energy = k * (q1 - q2)**2 / 2
+
+    #### Friction forces
+    forcelist = [(P1, - nu * q1d * N.x),
+                 (P2, - nu * q2d * N.x)]
+    lag = Lagrangian(N, pP1, pP2)
+
+    l_method = LagrangesMethod(lag, (q1, q2), forcelist=forcelist, frame=N)
+    l_method.form_lagranges_equations()
+
+    eq1 = l_method.eom[0]
+    assert eq1.diff(q1d) == nu
+    eq2 = l_method.eom[1]
+    assert eq2.diff(q2d) == nu