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ckpts/universal/global_step80/zero/15.input_layernorm.weight/exp_avg.pt

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+oid sha256:d03f5cc7d1db3d15cf919ab6fba361ee207dd5c5712b31271caf19bc2d00e779
+size 9372

venv/lib/python3.10/site-packages/networkx/algorithms/approximation/__init__.py

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+"""Approximations of graph properties and Heuristic methods for optimization.
+
+The functions in this class are not imported into the top-level ``networkx``
+namespace so the easiest way to use them is with::
+
+    >>> from networkx.algorithms import approximation
+
+Another option is to import the specific function with
+``from networkx.algorithms.approximation import function_name``.
+
+"""
+from networkx.algorithms.approximation.clustering_coefficient import *
+from networkx.algorithms.approximation.clique import *
+from networkx.algorithms.approximation.connectivity import *
+from networkx.algorithms.approximation.distance_measures import *
+from networkx.algorithms.approximation.dominating_set import *
+from networkx.algorithms.approximation.kcomponents import *
+from networkx.algorithms.approximation.matching import *
+from networkx.algorithms.approximation.ramsey import *
+from networkx.algorithms.approximation.steinertree import *
+from networkx.algorithms.approximation.traveling_salesman import *
+from networkx.algorithms.approximation.treewidth import *
+from networkx.algorithms.approximation.vertex_cover import *
+from networkx.algorithms.approximation.maxcut import *

venv/lib/python3.10/site-packages/networkx/algorithms/approximation/clique.py

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+"""Functions for computing large cliques and maximum independent sets."""
+import networkx as nx
+from networkx.algorithms.approximation import ramsey
+from networkx.utils import not_implemented_for
+
+__all__ = [
+    "clique_removal",
+    "max_clique",
+    "large_clique_size",
+    "maximum_independent_set",
+]
+
+
+@not_implemented_for("directed")
+@not_implemented_for("multigraph")
+@nx._dispatchable
+def maximum_independent_set(G):
+    """Returns an approximate maximum independent set.
+
+    Independent set or stable set is a set of vertices in a graph, no two of
+    which are adjacent. That is, it is a set I of vertices such that for every
+    two vertices in I, there is no edge connecting the two. Equivalently, each
+    edge in the graph has at most one endpoint in I. The size of an independent
+    set is the number of vertices it contains [1]_.
+
+    A maximum independent set is a largest independent set for a given graph G
+    and its size is denoted $\\alpha(G)$. The problem of finding such a set is called
+    the maximum independent set problem and is an NP-hard optimization problem.
+    As such, it is unlikely that there exists an efficient algorithm for finding
+    a maximum independent set of a graph.
+
+    The Independent Set algorithm is based on [2]_.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+        Undirected graph
+
+    Returns
+    -------
+    iset : Set
+        The apx-maximum independent set
+
+    Examples
+    --------
+    >>> G = nx.path_graph(10)
+    >>> nx.approximation.maximum_independent_set(G)
+    {0, 2, 4, 6, 9}
+
+    Raises
+    ------
+    NetworkXNotImplemented
+        If the graph is directed or is a multigraph.
+
+    Notes
+    -----
+    Finds the $O(|V|/(log|V|)^2)$ apx of independent set in the worst case.
+
+    References
+    ----------
+    .. [1] `Wikipedia: Independent set
+        <https://en.wikipedia.org/wiki/Independent_set_(graph_theory)>`_
+    .. [2] Boppana, R., & Halldórsson, M. M. (1992).
+       Approximating maximum independent sets by excluding subgraphs.
+       BIT Numerical Mathematics, 32(2), 180–196. Springer.
+    """
+    iset, _ = clique_removal(G)
+    return iset
+
+
+@not_implemented_for("directed")
+@not_implemented_for("multigraph")
+@nx._dispatchable
+def max_clique(G):
+    r"""Find the Maximum Clique
+
+    Finds the $O(|V|/(log|V|)^2)$ apx of maximum clique/independent set
+    in the worst case.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+        Undirected graph
+
+    Returns
+    -------
+    clique : set
+        The apx-maximum clique of the graph
+
+    Examples
+    --------
+    >>> G = nx.path_graph(10)
+    >>> nx.approximation.max_clique(G)
+    {8, 9}
+
+    Raises
+    ------
+    NetworkXNotImplemented
+        If the graph is directed or is a multigraph.
+
+    Notes
+    -----
+    A clique in an undirected graph G = (V, E) is a subset of the vertex set
+    `C \subseteq V` such that for every two vertices in C there exists an edge
+    connecting the two. This is equivalent to saying that the subgraph
+    induced by C is complete (in some cases, the term clique may also refer
+    to the subgraph).
+
+    A maximum clique is a clique of the largest possible size in a given graph.
+    The clique number `\omega(G)` of a graph G is the number of
+    vertices in a maximum clique in G. The intersection number of
+    G is the smallest number of cliques that together cover all edges of G.
+
+    https://en.wikipedia.org/wiki/Maximum_clique
+
+    References
+    ----------
+    .. [1] Boppana, R., & Halldórsson, M. M. (1992).
+        Approximating maximum independent sets by excluding subgraphs.
+        BIT Numerical Mathematics, 32(2), 180–196. Springer.
+        doi:10.1007/BF01994876
+    """
+    # finding the maximum clique in a graph is equivalent to finding
+    # the independent set in the complementary graph
+    cgraph = nx.complement(G)
+    iset, _ = clique_removal(cgraph)
+    return iset
+
+
+@not_implemented_for("directed")
+@not_implemented_for("multigraph")
+@nx._dispatchable
+def clique_removal(G):
+    r"""Repeatedly remove cliques from the graph.
+
+    Results in a $O(|V|/(\log |V|)^2)$ approximation of maximum clique
+    and independent set. Returns the largest independent set found, along
+    with found maximal cliques.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+        Undirected graph
+
+    Returns
+    -------
+    max_ind_cliques : (set, list) tuple
+        2-tuple of Maximal Independent Set and list of maximal cliques (sets).
+
+    Examples
+    --------
+    >>> G = nx.path_graph(10)
+    >>> nx.approximation.clique_removal(G)
+    ({0, 2, 4, 6, 9}, [{0, 1}, {2, 3}, {4, 5}, {6, 7}, {8, 9}])
+
+    Raises
+    ------
+    NetworkXNotImplemented
+        If the graph is directed or is a multigraph.
+
+    References
+    ----------
+    .. [1] Boppana, R., & Halldórsson, M. M. (1992).
+        Approximating maximum independent sets by excluding subgraphs.
+        BIT Numerical Mathematics, 32(2), 180–196. Springer.
+    """
+    graph = G.copy()
+    c_i, i_i = ramsey.ramsey_R2(graph)
+    cliques = [c_i]
+    isets = [i_i]
+    while graph:
+        graph.remove_nodes_from(c_i)
+        c_i, i_i = ramsey.ramsey_R2(graph)
+        if c_i:
+            cliques.append(c_i)
+        if i_i:
+            isets.append(i_i)
+    # Determine the largest independent set as measured by cardinality.
+    maxiset = max(isets, key=len)
+    return maxiset, cliques
+
+
+@not_implemented_for("directed")
+@not_implemented_for("multigraph")
+@nx._dispatchable
+def large_clique_size(G):
+    """Find the size of a large clique in a graph.
+
+    A *clique* is a subset of nodes in which each pair of nodes is
+    adjacent. This function is a heuristic for finding the size of a
+    large clique in the graph.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+
+    Returns
+    -------
+    k: integer
+       The size of a large clique in the graph.
+
+    Examples
+    --------
+    >>> G = nx.path_graph(10)
+    >>> nx.approximation.large_clique_size(G)
+    2
+
+    Raises
+    ------
+    NetworkXNotImplemented
+        If the graph is directed or is a multigraph.
+
+    Notes
+    -----
+    This implementation is from [1]_. Its worst case time complexity is
+    :math:`O(n d^2)`, where *n* is the number of nodes in the graph and
+    *d* is the maximum degree.
+
+    This function is a heuristic, which means it may work well in
+    practice, but there is no rigorous mathematical guarantee on the
+    ratio between the returned number and the actual largest clique size
+    in the graph.
+
+    References
+    ----------
+    .. [1] Pattabiraman, Bharath, et al.
+       "Fast Algorithms for the Maximum Clique Problem on Massive Graphs
+       with Applications to Overlapping Community Detection."
+       *Internet Mathematics* 11.4-5 (2015): 421--448.
+       <https://doi.org/10.1080/15427951.2014.986778>
+
+    See also
+    --------
+
+    :func:`networkx.algorithms.approximation.clique.max_clique`
+        A function that returns an approximate maximum clique with a
+        guarantee on the approximation ratio.
+
+    :mod:`networkx.algorithms.clique`
+        Functions for finding the exact maximum clique in a graph.
+
+    """
+    degrees = G.degree
+
+    def _clique_heuristic(G, U, size, best_size):
+        if not U:
+            return max(best_size, size)
+        u = max(U, key=degrees)
+        U.remove(u)
+        N_prime = {v for v in G[u] if degrees[v] >= best_size}
+        return _clique_heuristic(G, U & N_prime, size + 1, best_size)
+
+    best_size = 0
+    nodes = (u for u in G if degrees[u] >= best_size)
+    for u in nodes:
+        neighbors = {v for v in G[u] if degrees[v] >= best_size}
+        best_size = _clique_heuristic(G, neighbors, 1, best_size)
+    return best_size

venv/lib/python3.10/site-packages/networkx/algorithms/approximation/connectivity.py

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+""" Fast approximation for node connectivity
+"""
+import itertools
+from operator import itemgetter
+
+import networkx as nx
+
+__all__ = [
+    "local_node_connectivity",
+    "node_connectivity",
+    "all_pairs_node_connectivity",
+]
+
+
+@nx._dispatchable(name="approximate_local_node_connectivity")
+def local_node_connectivity(G, source, target, cutoff=None):
+    """Compute node connectivity between source and target.
+
+    Pairwise or local node connectivity between two distinct and nonadjacent
+    nodes is the minimum number of nodes that must be removed (minimum
+    separating cutset) to disconnect them. By Menger's theorem, this is equal
+    to the number of node independent paths (paths that share no nodes other
+    than source and target). Which is what we compute in this function.
+
+    This algorithm is a fast approximation that gives an strict lower
+    bound on the actual number of node independent paths between two nodes [1]_.
+    It works for both directed and undirected graphs.
+
+    Parameters
+    ----------
+
+    G : NetworkX graph
+
+    source : node
+        Starting node for node connectivity
+
+    target : node
+        Ending node for node connectivity
+
+    cutoff : integer
+        Maximum node connectivity to consider. If None, the minimum degree
+        of source or target is used as a cutoff. Default value None.
+
+    Returns
+    -------
+    k: integer
+       pairwise node connectivity
+
+    Examples
+    --------
+    >>> # Platonic octahedral graph has node connectivity 4
+    >>> # for each non adjacent node pair
+    >>> from networkx.algorithms import approximation as approx
+    >>> G = nx.octahedral_graph()
+    >>> approx.local_node_connectivity(G, 0, 5)
+    4
+
+    Notes
+    -----
+    This algorithm [1]_ finds node independents paths between two nodes by
+    computing their shortest path using BFS, marking the nodes of the path
+    found as 'used' and then searching other shortest paths excluding the
+    nodes marked as used until no more paths exist. It is not exact because
+    a shortest path could use nodes that, if the path were longer, may belong
+    to two different node independent paths. Thus it only guarantees an
+    strict lower bound on node connectivity.
+
+    Note that the authors propose a further refinement, losing accuracy and
+    gaining speed, which is not implemented yet.
+
+    See also
+    --------
+    all_pairs_node_connectivity
+    node_connectivity
+
+    References
+    ----------
+    .. [1] White, Douglas R., and Mark Newman. 2001 A Fast Algorithm for
+        Node-Independent Paths. Santa Fe Institute Working Paper #01-07-035
+        http://eclectic.ss.uci.edu/~drwhite/working.pdf
+
+    """
+    if target == source:
+        raise nx.NetworkXError("source and target have to be different nodes.")
+
+    # Maximum possible node independent paths
+    if G.is_directed():
+        possible = min(G.out_degree(source), G.in_degree(target))
+    else:
+        possible = min(G.degree(source), G.degree(target))
+
+    K = 0
+    if not possible:
+        return K
+
+    if cutoff is None:
+        cutoff = float("inf")
+
+    exclude = set()
+    for i in range(min(possible, cutoff)):
+        try:
+            path = _bidirectional_shortest_path(G, source, target, exclude)
+            exclude.update(set(path))
+            K += 1
+        except nx.NetworkXNoPath:
+            break
+
+    return K
+
+
+@nx._dispatchable(name="approximate_node_connectivity")
+def node_connectivity(G, s=None, t=None):
+    r"""Returns an approximation for node connectivity for a graph or digraph G.
+
+    Node connectivity is equal to the minimum number of nodes that
+    must be removed to disconnect G or render it trivial. By Menger's theorem,
+    this is equal to the number of node independent paths (paths that
+    share no nodes other than source and target).
+
+    If source and target nodes are provided, this function returns the
+    local node connectivity: the minimum number of nodes that must be
+    removed to break all paths from source to target in G.
+
+    This algorithm is based on a fast approximation that gives an strict lower
+    bound on the actual number of node independent paths between two nodes [1]_.
+    It works for both directed and undirected graphs.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+        Undirected graph
+
+    s : node
+        Source node. Optional. Default value: None.
+
+    t : node
+        Target node. Optional. Default value: None.
+
+    Returns
+    -------
+    K : integer
+        Node connectivity of G, or local node connectivity if source
+        and target are provided.
+
+    Examples
+    --------
+    >>> # Platonic octahedral graph is 4-node-connected
+    >>> from networkx.algorithms import approximation as approx
+    >>> G = nx.octahedral_graph()
+    >>> approx.node_connectivity(G)
+    4
+
+    Notes
+    -----
+    This algorithm [1]_ finds node independents paths between two nodes by
+    computing their shortest path using BFS, marking the nodes of the path
+    found as 'used' and then searching other shortest paths excluding the
+    nodes marked as used until no more paths exist. It is not exact because
+    a shortest path could use nodes that, if the path were longer, may belong
+    to two different node independent paths. Thus it only guarantees an
+    strict lower bound on node connectivity.
+
+    See also
+    --------
+    all_pairs_node_connectivity
+    local_node_connectivity
+
+    References
+    ----------
+    .. [1] White, Douglas R., and Mark Newman. 2001 A Fast Algorithm for
+        Node-Independent Paths. Santa Fe Institute Working Paper #01-07-035
+        http://eclectic.ss.uci.edu/~drwhite/working.pdf
+
+    """
+    if (s is not None and t is None) or (s is None and t is not None):
+        raise nx.NetworkXError("Both source and target must be specified.")
+
+    # Local node connectivity
+    if s is not None and t is not None:
+        if s not in G:
+            raise nx.NetworkXError(f"node {s} not in graph")
+        if t not in G:
+            raise nx.NetworkXError(f"node {t} not in graph")
+        return local_node_connectivity(G, s, t)
+
+    # Global node connectivity
+    if G.is_directed():
+        connected_func = nx.is_weakly_connected
+        iter_func = itertools.permutations
+
+        def neighbors(v):
+            return itertools.chain(G.predecessors(v), G.successors(v))
+
+    else:
+        connected_func = nx.is_connected
+        iter_func = itertools.combinations
+        neighbors = G.neighbors
+
+    if not connected_func(G):
+        return 0
+
+    # Choose a node with minimum degree
+    v, minimum_degree = min(G.degree(), key=itemgetter(1))
+    # Node connectivity is bounded by minimum degree
+    K = minimum_degree
+    # compute local node connectivity with all non-neighbors nodes
+    # and store the minimum
+    for w in set(G) - set(neighbors(v)) - {v}:
+        K = min(K, local_node_connectivity(G, v, w, cutoff=K))
+    # Same for non adjacent pairs of neighbors of v
+    for x, y in iter_func(neighbors(v), 2):
+        if y not in G[x] and x != y:
+            K = min(K, local_node_connectivity(G, x, y, cutoff=K))
+    return K
+
+
+@nx._dispatchable(name="approximate_all_pairs_node_connectivity")
+def all_pairs_node_connectivity(G, nbunch=None, cutoff=None):
+    """Compute node connectivity between all pairs of nodes.
+
+    Pairwise or local node connectivity between two distinct and nonadjacent
+    nodes is the minimum number of nodes that must be removed (minimum
+    separating cutset) to disconnect them. By Menger's theorem, this is equal
+    to the number of node independent paths (paths that share no nodes other
+    than source and target). Which is what we compute in this function.
+
+    This algorithm is a fast approximation that gives an strict lower
+    bound on the actual number of node independent paths between two nodes [1]_.
+    It works for both directed and undirected graphs.
+
+
+    Parameters
+    ----------
+    G : NetworkX graph
+
+    nbunch: container
+        Container of nodes. If provided node connectivity will be computed
+        only over pairs of nodes in nbunch.
+
+    cutoff : integer
+        Maximum node connectivity to consider. If None, the minimum degree
+        of source or target is used as a cutoff in each pair of nodes.
+        Default value None.
+
+    Returns
+    -------
+    K : dictionary
+        Dictionary, keyed by source and target, of pairwise node connectivity
+
+    Examples
+    --------
+    A 3 node cycle with one extra node attached has connectivity 2 between all
+    nodes in the cycle and connectivity 1 between the extra node and the rest:
+
+    >>> G = nx.cycle_graph(3)
+    >>> G.add_edge(2, 3)
+    >>> import pprint  # for nice dictionary formatting
+    >>> pprint.pprint(nx.all_pairs_node_connectivity(G))
+    {0: {1: 2, 2: 2, 3: 1},
+     1: {0: 2, 2: 2, 3: 1},
+     2: {0: 2, 1: 2, 3: 1},
+     3: {0: 1, 1: 1, 2: 1}}
+
+    See Also
+    --------
+    local_node_connectivity
+    node_connectivity
+
+    References
+    ----------
+    .. [1] White, Douglas R., and Mark Newman. 2001 A Fast Algorithm for
+        Node-Independent Paths. Santa Fe Institute Working Paper #01-07-035
+        http://eclectic.ss.uci.edu/~drwhite/working.pdf
+    """
+    if nbunch is None:
+        nbunch = G
+    else:
+        nbunch = set(nbunch)
+
+    directed = G.is_directed()
+    if directed:
+        iter_func = itertools.permutations
+    else:
+        iter_func = itertools.combinations
+
+    all_pairs = {n: {} for n in nbunch}
+
+    for u, v in iter_func(nbunch, 2):
+        k = local_node_connectivity(G, u, v, cutoff=cutoff)
+        all_pairs[u][v] = k
+        if not directed:
+            all_pairs[v][u] = k
+
+    return all_pairs
+
+
+def _bidirectional_shortest_path(G, source, target, exclude):
+    """Returns shortest path between source and target ignoring nodes in the
+    container 'exclude'.
+
+    Parameters
+    ----------
+
+    G : NetworkX graph
+
+    source : node
+        Starting node for path
+
+    target : node
+        Ending node for path
+
+    exclude: container
+        Container for nodes to exclude from the search for shortest paths
+
+    Returns
+    -------
+    path: list
+        Shortest path between source and target ignoring nodes in 'exclude'
+
+    Raises
+    ------
+    NetworkXNoPath
+        If there is no path or if nodes are adjacent and have only one path
+        between them
+
+    Notes
+    -----
+    This function and its helper are originally from
+    networkx.algorithms.shortest_paths.unweighted and are modified to
+    accept the extra parameter 'exclude', which is a container for nodes
+    already used in other paths that should be ignored.
+
+    References
+    ----------
+    .. [1] White, Douglas R., and Mark Newman. 2001 A Fast Algorithm for
+        Node-Independent Paths. Santa Fe Institute Working Paper #01-07-035
+        http://eclectic.ss.uci.edu/~drwhite/working.pdf
+
+    """
+    # call helper to do the real work
+    results = _bidirectional_pred_succ(G, source, target, exclude)
+    pred, succ, w = results
+
+    # build path from pred+w+succ
+    path = []
+    # from source to w
+    while w is not None:
+        path.append(w)
+        w = pred[w]
+    path.reverse()
+    # from w to target
+    w = succ[path[-1]]
+    while w is not None:
+        path.append(w)
+        w = succ[w]
+
+    return path
+
+
+def _bidirectional_pred_succ(G, source, target, exclude):
+    # does BFS from both source and target and meets in the middle
+    # excludes nodes in the container "exclude" from the search
+
+    # handle either directed or undirected
+    if G.is_directed():
+        Gpred = G.predecessors
+        Gsucc = G.successors
+    else:
+        Gpred = G.neighbors
+        Gsucc = G.neighbors
+
+    # predecessor and successors in search
+    pred = {source: None}
+    succ = {target: None}
+
+    # initialize fringes, start with forward
+    forward_fringe = [source]
+    reverse_fringe = [target]
+
+    level = 0
+
+    while forward_fringe and reverse_fringe:
+        # Make sure that we iterate one step forward and one step backwards
+        # thus source and target will only trigger "found path" when they are
+        # adjacent and then they can be safely included in the container 'exclude'
+        level += 1
+        if level % 2 != 0:
+            this_level = forward_fringe
+            forward_fringe = []
+            for v in this_level:
+                for w in Gsucc(v):
+                    if w in exclude:
+                        continue
+                    if w not in pred:
+                        forward_fringe.append(w)
+                        pred[w] = v
+                    if w in succ:
+                        return pred, succ, w  # found path
+        else:
+            this_level = reverse_fringe
+            reverse_fringe = []
+            for v in this_level:
+                for w in Gpred(v):
+                    if w in exclude:
+                        continue
+                    if w not in succ:
+                        succ[w] = v
+                        reverse_fringe.append(w)
+                    if w in pred:
+                        return pred, succ, w  # found path
+
+    raise nx.NetworkXNoPath(f"No path between {source} and {target}.")

venv/lib/python3.10/site-packages/networkx/algorithms/approximation/distance_measures.py

@@ -0,0 +1,150 @@
+"""Distance measures approximated metrics."""
+
+import networkx as nx
+from networkx.utils.decorators import py_random_state
+
+__all__ = ["diameter"]
+
+
+@py_random_state(1)
+@nx._dispatchable(name="approximate_diameter")
+def diameter(G, seed=None):
+    """Returns a lower bound on the diameter of the graph G.
+
+    The function computes a lower bound on the diameter (i.e., the maximum eccentricity)
+    of a directed or undirected graph G. The procedure used varies depending on the graph
+    being directed or not.
+
+    If G is an `undirected` graph, then the function uses the `2-sweep` algorithm [1]_.
+    The main idea is to pick the farthest node from a random node and return its eccentricity.
+
+    Otherwise, if G is a `directed` graph, the function uses the `2-dSweep` algorithm [2]_,
+    The procedure starts by selecting a random source node $s$ from which it performs a
+    forward and a backward BFS. Let $a_1$ and $a_2$ be the farthest nodes in the forward and
+    backward cases, respectively. Then, it computes the backward eccentricity of $a_1$ using
+    a backward BFS and the forward eccentricity of $a_2$ using a forward BFS.
+    Finally, it returns the best lower bound between the two.
+
+    In both cases, the time complexity is linear with respect to the size of G.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+
+    seed : integer, random_state, or None (default)
+        Indicator of random number generation state.
+        See :ref:`Randomness<randomness>`.
+
+    Returns
+    -------
+    d : integer
+       Lower Bound on the Diameter of G
+
+    Examples
+    --------
+    >>> G = nx.path_graph(10)  # undirected graph
+    >>> nx.diameter(G)
+    9
+    >>> G = nx.cycle_graph(3, create_using=nx.DiGraph)  # directed graph
+    >>> nx.diameter(G)
+    2
+
+    Raises
+    ------
+    NetworkXError
+        If the graph is empty or
+        If the graph is undirected and not connected or
+        If the graph is directed and not strongly connected.
+
+    See Also
+    --------
+    networkx.algorithms.distance_measures.diameter
+
+    References
+    ----------
+    .. [1] Magnien, Clémence, Matthieu Latapy, and Michel Habib.
+       *Fast computation of empirically tight bounds for the diameter of massive graphs.*
+       Journal of Experimental Algorithmics (JEA), 2009.
+       https://arxiv.org/pdf/0904.2728.pdf
+    .. [2] Crescenzi, Pierluigi, Roberto Grossi, Leonardo Lanzi, and Andrea Marino.
+       *On computing the diameter of real-world directed (weighted) graphs.*
+       International Symposium on Experimental Algorithms. Springer, Berlin, Heidelberg, 2012.
+       https://courses.cs.ut.ee/MTAT.03.238/2014_fall/uploads/Main/diameter.pdf
+    """
+    # if G is empty
+    if not G:
+        raise nx.NetworkXError("Expected non-empty NetworkX graph!")
+    # if there's only a node
+    if G.number_of_nodes() == 1:
+        return 0
+    # if G is directed
+    if G.is_directed():
+        return _two_sweep_directed(G, seed)
+    # else if G is undirected
+    return _two_sweep_undirected(G, seed)
+
+
+def _two_sweep_undirected(G, seed):
+    """Helper function for finding a lower bound on the diameter
+        for undirected Graphs.
+
+        The idea is to pick the farthest node from a random node
+        and return its eccentricity.
+
+        ``G`` is a NetworkX undirected graph.
+
+    .. note::
+
+        ``seed`` is a random.Random or numpy.random.RandomState instance
+    """
+    # select a random source node
+    source = seed.choice(list(G))
+    # get the distances to the other nodes
+    distances = nx.shortest_path_length(G, source)
+    # if some nodes have not been visited, then the graph is not connected
+    if len(distances) != len(G):
+        raise nx.NetworkXError("Graph not connected.")
+    # take a node that is (one of) the farthest nodes from the source
+    *_, node = distances
+    # return the eccentricity of the node
+    return nx.eccentricity(G, node)
+
+
+def _two_sweep_directed(G, seed):
+    """Helper function for finding a lower bound on the diameter
+        for directed Graphs.
+
+        It implements 2-dSweep, the directed version of the 2-sweep algorithm.
+        The algorithm follows the following steps.
+        1. Select a source node $s$ at random.
+        2. Perform a forward BFS from $s$ to select a node $a_1$ at the maximum
+        distance from the source, and compute $LB_1$, the backward eccentricity of $a_1$.
+        3. Perform a backward BFS from $s$ to select a node $a_2$ at the maximum
+        distance from the source, and compute $LB_2$, the forward eccentricity of $a_2$.
+        4. Return the maximum between $LB_1$ and $LB_2$.
+
+        ``G`` is a NetworkX directed graph.
+
+    .. note::
+
+        ``seed`` is a random.Random or numpy.random.RandomState instance
+    """
+    # get a new digraph G' with the edges reversed in the opposite direction
+    G_reversed = G.reverse()
+    # select a random source node
+    source = seed.choice(list(G))
+    # compute forward distances from source
+    forward_distances = nx.shortest_path_length(G, source)
+    # compute backward distances  from source
+    backward_distances = nx.shortest_path_length(G_reversed, source)
+    # if either the source can't reach every node or not every node
+    # can reach the source, then the graph is not strongly connected
+    n = len(G)
+    if len(forward_distances) != n or len(backward_distances) != n:
+        raise nx.NetworkXError("DiGraph not strongly connected.")
+    # take a node a_1 at the maximum distance from the source in G
+    *_, a_1 = forward_distances
+    # take a node a_2 at the maximum distance from the source in G_reversed
+    *_, a_2 = backward_distances
+    # return the max between the backward eccentricity of a_1 and the forward eccentricity of a_2
+    return max(nx.eccentricity(G_reversed, a_1), nx.eccentricity(G, a_2))

venv/lib/python3.10/site-packages/networkx/algorithms/approximation/dominating_set.py

@@ -0,0 +1,148 @@
+"""Functions for finding node and edge dominating sets.
+
+A `dominating set`_ for an undirected graph *G* with vertex set *V*
+and edge set *E* is a subset *D* of *V* such that every vertex not in
+*D* is adjacent to at least one member of *D*. An `edge dominating set`_
+is a subset *F* of *E* such that every edge not in *F* is
+incident to an endpoint of at least one edge in *F*.
+
+.. _dominating set: https://en.wikipedia.org/wiki/Dominating_set
+.. _edge dominating set: https://en.wikipedia.org/wiki/Edge_dominating_set
+
+"""
+import networkx as nx
+
+from ...utils import not_implemented_for
+from ..matching import maximal_matching
+
+__all__ = ["min_weighted_dominating_set", "min_edge_dominating_set"]
+
+
+# TODO Why doesn't this algorithm work for directed graphs?
+@not_implemented_for("directed")
+@nx._dispatchable(node_attrs="weight")
+def min_weighted_dominating_set(G, weight=None):
+    r"""Returns a dominating set that approximates the minimum weight node
+    dominating set.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+        Undirected graph.
+
+    weight : string
+        The node attribute storing the weight of an node. If provided,
+        the node attribute with this key must be a number for each
+        node. If not provided, each node is assumed to have weight one.
+
+    Returns
+    -------
+    min_weight_dominating_set : set
+        A set of nodes, the sum of whose weights is no more than `(\log
+        w(V)) w(V^*)`, where `w(V)` denotes the sum of the weights of
+        each node in the graph and `w(V^*)` denotes the sum of the
+        weights of each node in the minimum weight dominating set.
+
+    Examples
+    --------
+    >>> G = nx.Graph([(0, 1), (0, 4), (1, 4), (1, 2), (2, 3), (3, 4), (2, 5)])
+    >>> nx.approximation.min_weighted_dominating_set(G)
+    {1, 2, 4}
+
+    Raises
+    ------
+    NetworkXNotImplemented
+        If G is directed.
+
+    Notes
+    -----
+    This algorithm computes an approximate minimum weighted dominating
+    set for the graph `G`. The returned solution has weight `(\log
+    w(V)) w(V^*)`, where `w(V)` denotes the sum of the weights of each
+    node in the graph and `w(V^*)` denotes the sum of the weights of
+    each node in the minimum weight dominating set for the graph.
+
+    This implementation of the algorithm runs in $O(m)$ time, where $m$
+    is the number of edges in the graph.
+
+    References
+    ----------
+    .. [1] Vazirani, Vijay V.
+           *Approximation Algorithms*.
+           Springer Science & Business Media, 2001.
+
+    """
+    # The unique dominating set for the null graph is the empty set.
+    if len(G) == 0:
+        return set()
+
+    # This is the dominating set that will eventually be returned.
+    dom_set = set()
+
+    def _cost(node_and_neighborhood):
+        """Returns the cost-effectiveness of greedily choosing the given
+        node.
+
+        `node_and_neighborhood` is a two-tuple comprising a node and its
+        closed neighborhood.
+
+        """
+        v, neighborhood = node_and_neighborhood
+        return G.nodes[v].get(weight, 1) / len(neighborhood - dom_set)
+
+    # This is a set of all vertices not already covered by the
+    # dominating set.
+    vertices = set(G)
+    # This is a dictionary mapping each node to the closed neighborhood
+    # of that node.
+    neighborhoods = {v: {v} | set(G[v]) for v in G}
+
+    # Continue until all vertices are adjacent to some node in the
+    # dominating set.
+    while vertices:
+        # Find the most cost-effective node to add, along with its
+        # closed neighborhood.
+        dom_node, min_set = min(neighborhoods.items(), key=_cost)
+        # Add the node to the dominating set and reduce the remaining
+        # set of nodes to cover.
+        dom_set.add(dom_node)
+        del neighborhoods[dom_node]
+        vertices -= min_set
+
+    return dom_set
+
+
+@nx._dispatchable
+def min_edge_dominating_set(G):
+    r"""Returns minimum cardinality edge dominating set.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+      Undirected graph
+
+    Returns
+    -------
+    min_edge_dominating_set : set
+      Returns a set of dominating edges whose size is no more than 2 * OPT.
+
+    Examples
+    --------
+    >>> G = nx.petersen_graph()
+    >>> nx.approximation.min_edge_dominating_set(G)
+    {(0, 1), (4, 9), (6, 8), (5, 7), (2, 3)}
+
+    Raises
+    ------
+    ValueError
+        If the input graph `G` is empty.
+
+    Notes
+    -----
+    The algorithm computes an approximate solution to the edge dominating set
+    problem. The result is no more than 2 * OPT in terms of size of the set.
+    Runtime of the algorithm is $O(|E|)$.
+    """
+    if not G:
+        raise ValueError("Expected non-empty NetworkX graph!")
+    return maximal_matching(G)

venv/lib/python3.10/site-packages/networkx/algorithms/approximation/kcomponents.py

@@ -0,0 +1,369 @@
+""" Fast approximation for k-component structure
+"""
+import itertools
+from collections import defaultdict
+from collections.abc import Mapping
+from functools import cached_property
+
+import networkx as nx
+from networkx.algorithms.approximation import local_node_connectivity
+from networkx.exception import NetworkXError
+from networkx.utils import not_implemented_for
+
+__all__ = ["k_components"]
+
+
+@not_implemented_for("directed")
+@nx._dispatchable(name="approximate_k_components")
+def k_components(G, min_density=0.95):
+    r"""Returns the approximate k-component structure of a graph G.
+
+    A `k`-component is a maximal subgraph of a graph G that has, at least,
+    node connectivity `k`: we need to remove at least `k` nodes to break it
+    into more components. `k`-components have an inherent hierarchical
+    structure because they are nested in terms of connectivity: a connected
+    graph can contain several 2-components, each of which can contain
+    one or more 3-components, and so forth.
+
+    This implementation is based on the fast heuristics to approximate
+    the `k`-component structure of a graph [1]_. Which, in turn, it is based on
+    a fast approximation algorithm for finding good lower bounds of the number
+    of node independent paths between two nodes [2]_.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+        Undirected graph
+
+    min_density : Float
+        Density relaxation threshold. Default value 0.95
+
+    Returns
+    -------
+    k_components : dict
+        Dictionary with connectivity level `k` as key and a list of
+        sets of nodes that form a k-component of level `k` as values.
+
+    Raises
+    ------
+    NetworkXNotImplemented
+        If G is directed.
+
+    Examples
+    --------
+    >>> # Petersen graph has 10 nodes and it is triconnected, thus all
+    >>> # nodes are in a single component on all three connectivity levels
+    >>> from networkx.algorithms import approximation as apxa
+    >>> G = nx.petersen_graph()
+    >>> k_components = apxa.k_components(G)
+
+    Notes
+    -----
+    The logic of the approximation algorithm for computing the `k`-component
+    structure [1]_ is based on repeatedly applying simple and fast algorithms
+    for `k`-cores and biconnected components in order to narrow down the
+    number of pairs of nodes over which we have to compute White and Newman's
+    approximation algorithm for finding node independent paths [2]_. More
+    formally, this algorithm is based on Whitney's theorem, which states
+    an inclusion relation among node connectivity, edge connectivity, and
+    minimum degree for any graph G. This theorem implies that every
+    `k`-component is nested inside a `k`-edge-component, which in turn,
+    is contained in a `k`-core. Thus, this algorithm computes node independent
+    paths among pairs of nodes in each biconnected part of each `k`-core,
+    and repeats this procedure for each `k` from 3 to the maximal core number
+    of a node in the input graph.
+
+    Because, in practice, many nodes of the core of level `k` inside a
+    bicomponent actually are part of a component of level k, the auxiliary
+    graph needed for the algorithm is likely to be very dense. Thus, we use
+    a complement graph data structure (see `AntiGraph`) to save memory.
+    AntiGraph only stores information of the edges that are *not* present
+    in the actual auxiliary graph. When applying algorithms to this
+    complement graph data structure, it behaves as if it were the dense
+    version.
+
+    See also
+    --------
+    k_components
+
+    References
+    ----------
+    .. [1]  Torrents, J. and F. Ferraro (2015) Structural Cohesion:
+            Visualization and Heuristics for Fast Computation.
+            https://arxiv.org/pdf/1503.04476v1
+
+    .. [2]  White, Douglas R., and Mark Newman (2001) A Fast Algorithm for
+            Node-Independent Paths. Santa Fe Institute Working Paper #01-07-035
+            https://www.santafe.edu/research/results/working-papers/fast-approximation-algorithms-for-finding-node-ind
+
+    .. [3]  Moody, J. and D. White (2003). Social cohesion and embeddedness:
+            A hierarchical conception of social groups.
+            American Sociological Review 68(1), 103--28.
+            https://doi.org/10.2307/3088904
+
+    """
+    # Dictionary with connectivity level (k) as keys and a list of
+    # sets of nodes that form a k-component as values
+    k_components = defaultdict(list)
+    # make a few functions local for speed
+    node_connectivity = local_node_connectivity
+    k_core = nx.k_core
+    core_number = nx.core_number
+    biconnected_components = nx.biconnected_components
+    combinations = itertools.combinations
+    # Exact solution for k = {1,2}
+    # There is a linear time algorithm for triconnectivity, if we had an
+    # implementation available we could start from k = 4.
+    for component in nx.connected_components(G):
+        # isolated nodes have connectivity 0
+        comp = set(component)
+        if len(comp) > 1:
+            k_components[1].append(comp)
+    for bicomponent in nx.biconnected_components(G):
+        # avoid considering dyads as bicomponents
+        bicomp = set(bicomponent)
+        if len(bicomp) > 2:
+            k_components[2].append(bicomp)
+    # There is no k-component of k > maximum core number
+    # \kappa(G) <= \lambda(G) <= \delta(G)
+    g_cnumber = core_number(G)
+    max_core = max(g_cnumber.values())
+    for k in range(3, max_core + 1):
+        C = k_core(G, k, core_number=g_cnumber)
+        for nodes in biconnected_components(C):
+            # Build a subgraph SG induced by the nodes that are part of
+            # each biconnected component of the k-core subgraph C.
+            if len(nodes) < k:
+                continue
+            SG = G.subgraph(nodes)
+            # Build auxiliary graph
+            H = _AntiGraph()
+            H.add_nodes_from(SG.nodes())
+            for u, v in combinations(SG, 2):
+                K = node_connectivity(SG, u, v, cutoff=k)
+                if k > K:
+                    H.add_edge(u, v)
+            for h_nodes in biconnected_components(H):
+                if len(h_nodes) <= k:
+                    continue
+                SH = H.subgraph(h_nodes)
+                for Gc in _cliques_heuristic(SG, SH, k, min_density):
+                    for k_nodes in biconnected_components(Gc):
+                        Gk = nx.k_core(SG.subgraph(k_nodes), k)
+                        if len(Gk) <= k:
+                            continue
+                        k_components[k].append(set(Gk))
+    return k_components
+
+
+def _cliques_heuristic(G, H, k, min_density):
+    h_cnumber = nx.core_number(H)
+    for i, c_value in enumerate(sorted(set(h_cnumber.values()), reverse=True)):
+        cands = {n for n, c in h_cnumber.items() if c == c_value}
+        # Skip checking for overlap for the highest core value
+        if i == 0:
+            overlap = False
+        else:
+            overlap = set.intersection(
+                *[{x for x in H[n] if x not in cands} for n in cands]
+            )
+        if overlap and len(overlap) < k:
+            SH = H.subgraph(cands | overlap)
+        else:
+            SH = H.subgraph(cands)
+        sh_cnumber = nx.core_number(SH)
+        SG = nx.k_core(G.subgraph(SH), k)
+        while not (_same(sh_cnumber) and nx.density(SH) >= min_density):
+            # This subgraph must be writable => .copy()
+            SH = H.subgraph(SG).copy()
+            if len(SH) <= k:
+                break
+            sh_cnumber = nx.core_number(SH)
+            sh_deg = dict(SH.degree())
+            min_deg = min(sh_deg.values())
+            SH.remove_nodes_from(n for n, d in sh_deg.items() if d == min_deg)
+            SG = nx.k_core(G.subgraph(SH), k)
+        else:
+            yield SG
+
+
+def _same(measure, tol=0):
+    vals = set(measure.values())
+    if (max(vals) - min(vals)) <= tol:
+        return True
+    return False
+
+
+class _AntiGraph(nx.Graph):
+    """
+    Class for complement graphs.
+
+    The main goal is to be able to work with big and dense graphs with
+    a low memory footprint.
+
+    In this class you add the edges that *do not exist* in the dense graph,
+    the report methods of the class return the neighbors, the edges and
+    the degree as if it was the dense graph. Thus it's possible to use
+    an instance of this class with some of NetworkX functions. In this
+    case we only use k-core, connected_components, and biconnected_components.
+    """
+
+    all_edge_dict = {"weight": 1}
+
+    def single_edge_dict(self):
+        return self.all_edge_dict
+
+    edge_attr_dict_factory = single_edge_dict  # type: ignore[assignment]
+
+    def __getitem__(self, n):
+        """Returns a dict of neighbors of node n in the dense graph.
+
+        Parameters
+        ----------
+        n : node
+           A node in the graph.
+
+        Returns
+        -------
+        adj_dict : dictionary
+           The adjacency dictionary for nodes connected to n.
+
+        """
+        all_edge_dict = self.all_edge_dict
+        return {
+            node: all_edge_dict for node in set(self._adj) - set(self._adj[n]) - {n}
+        }
+
+    def neighbors(self, n):
+        """Returns an iterator over all neighbors of node n in the
+        dense graph.
+        """
+        try:
+            return iter(set(self._adj) - set(self._adj[n]) - {n})
+        except KeyError as err:
+            raise NetworkXError(f"The node {n} is not in the graph.") from err
+
+    class AntiAtlasView(Mapping):
+        """An adjacency inner dict for AntiGraph"""
+
+        def __init__(self, graph, node):
+            self._graph = graph
+            self._atlas = graph._adj[node]
+            self._node = node
+
+        def __len__(self):
+            return len(self._graph) - len(self._atlas) - 1
+
+        def __iter__(self):
+            return (n for n in self._graph if n not in self._atlas and n != self._node)
+
+        def __getitem__(self, nbr):
+            nbrs = set(self._graph._adj) - set(self._atlas) - {self._node}
+            if nbr in nbrs:
+                return self._graph.all_edge_dict
+            raise KeyError(nbr)
+
+    class AntiAdjacencyView(AntiAtlasView):
+        """An adjacency outer dict for AntiGraph"""
+
+        def __init__(self, graph):
+            self._graph = graph
+            self._atlas = graph._adj
+
+        def __len__(self):
+            return len(self._atlas)
+
+        def __iter__(self):
+            return iter(self._graph)
+
+        def __getitem__(self, node):
+            if node not in self._graph:
+                raise KeyError(node)
+            return self._graph.AntiAtlasView(self._graph, node)
+
+    @cached_property
+    def adj(self):
+        return self.AntiAdjacencyView(self)
+
+    def subgraph(self, nodes):
+        """This subgraph method returns a full AntiGraph. Not a View"""
+        nodes = set(nodes)
+        G = _AntiGraph()
+        G.add_nodes_from(nodes)
+        for n in G:
+            Gnbrs = G.adjlist_inner_dict_factory()
+            G._adj[n] = Gnbrs
+            for nbr, d in self._adj[n].items():
+                if nbr in G._adj:
+                    Gnbrs[nbr] = d
+                    G._adj[nbr][n] = d
+        G.graph = self.graph
+        return G
+
+    class AntiDegreeView(nx.reportviews.DegreeView):
+        def __iter__(self):
+            all_nodes = set(self._succ)
+            for n in self._nodes:
+                nbrs = all_nodes - set(self._succ[n]) - {n}
+                yield (n, len(nbrs))
+
+        def __getitem__(self, n):
+            nbrs = set(self._succ) - set(self._succ[n]) - {n}
+            # AntiGraph is a ThinGraph so all edges have weight 1
+            return len(nbrs) + (n in nbrs)
+
+    @cached_property
+    def degree(self):
+        """Returns an iterator for (node, degree) and degree for single node.
+
+        The node degree is the number of edges adjacent to the node.
+
+        Parameters
+        ----------
+        nbunch : iterable container, optional (default=all nodes)
+            A container of nodes.  The container will be iterated
+            through once.
+
+        weight : string or None, optional (default=None)
+           The edge attribute that holds the numerical value used
+           as a weight.  If None, then each edge has weight 1.
+           The degree is the sum of the edge weights adjacent to the node.
+
+        Returns
+        -------
+        deg:
+            Degree of the node, if a single node is passed as argument.
+        nd_iter : an iterator
+            The iterator returns two-tuples of (node, degree).
+
+        See Also
+        --------
+        degree
+
+        Examples
+        --------
+        >>> G = nx.path_graph(4)
+        >>> G.degree(0)  # node 0 with degree 1
+        1
+        >>> list(G.degree([0, 1]))
+        [(0, 1), (1, 2)]
+
+        """
+        return self.AntiDegreeView(self)
+
+    def adjacency(self):
+        """Returns an iterator of (node, adjacency set) tuples for all nodes
+           in the dense graph.
+
+        This is the fastest way to look at every edge.
+        For directed graphs, only outgoing adjacencies are included.
+
+        Returns
+        -------
+        adj_iter : iterator
+           An iterator of (node, adjacency set) for all nodes in
+           the graph.
+
+        """
+        for n in self._adj:
+            yield (n, set(self._adj) - set(self._adj[n]) - {n})

venv/lib/python3.10/site-packages/networkx/algorithms/approximation/matching.py

@@ -0,0 +1,43 @@
+"""
+**************
+Graph Matching
+**************
+
+Given a graph G = (V,E), a matching M in G is a set of pairwise non-adjacent
+edges; that is, no two edges share a common vertex.
+
+`Wikipedia: Matching <https://en.wikipedia.org/wiki/Matching_(graph_theory)>`_
+"""
+import networkx as nx
+
+__all__ = ["min_maximal_matching"]
+
+
+@nx._dispatchable
+def min_maximal_matching(G):
+    r"""Returns the minimum maximal matching of G. That is, out of all maximal
+    matchings of the graph G, the smallest is returned.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+      Undirected graph
+
+    Returns
+    -------
+    min_maximal_matching : set
+      Returns a set of edges such that no two edges share a common endpoint
+      and every edge not in the set shares some common endpoint in the set.
+      Cardinality will be 2*OPT in the worst case.
+
+    Notes
+    -----
+    The algorithm computes an approximate solution for the minimum maximal
+    cardinality matching problem. The solution is no more than 2 * OPT in size.
+    Runtime is $O(|E|)$.
+
+    References
+    ----------
+    .. [1] Vazirani, Vijay Approximation Algorithms (2001)
+    """
+    return nx.maximal_matching(G)

venv/lib/python3.10/site-packages/networkx/algorithms/approximation/maxcut.py

@@ -0,0 +1,143 @@
+import networkx as nx
+from networkx.utils.decorators import not_implemented_for, py_random_state
+
+__all__ = ["randomized_partitioning", "one_exchange"]
+
+
+@not_implemented_for("directed")
+@not_implemented_for("multigraph")
+@py_random_state(1)
+@nx._dispatchable(edge_attrs="weight")
+def randomized_partitioning(G, seed=None, p=0.5, weight=None):
+    """Compute a random partitioning of the graph nodes and its cut value.
+
+    A partitioning is calculated by observing each node
+    and deciding to add it to the partition with probability `p`,
+    returning a random cut and its corresponding value (the
+    sum of weights of edges connecting different partitions).
+
+    Parameters
+    ----------
+    G : NetworkX graph
+
+    seed : integer, random_state, or None (default)
+        Indicator of random number generation state.
+        See :ref:`Randomness<randomness>`.
+
+    p : scalar
+        Probability for each node to be part of the first partition.
+        Should be in [0,1]
+
+    weight : object
+        Edge attribute key to use as weight. If not specified, edges
+        have weight one.
+
+    Returns
+    -------
+    cut_size : scalar
+        Value of the minimum cut.
+
+    partition : pair of node sets
+        A partitioning of the nodes that defines a minimum cut.
+
+    Examples
+    --------
+    >>> G = nx.complete_graph(5)
+    >>> cut_size, partition = nx.approximation.randomized_partitioning(G, seed=1)
+    >>> cut_size
+    6
+    >>> partition
+    ({0, 3, 4}, {1, 2})
+
+    Raises
+    ------
+    NetworkXNotImplemented
+        If the graph is directed or is a multigraph.
+    """
+    cut = {node for node in G.nodes() if seed.random() < p}
+    cut_size = nx.algorithms.cut_size(G, cut, weight=weight)
+    partition = (cut, G.nodes - cut)
+    return cut_size, partition
+
+
+def _swap_node_partition(cut, node):
+    return cut - {node} if node in cut else cut.union({node})
+
+
+@not_implemented_for("directed")
+@not_implemented_for("multigraph")
+@py_random_state(2)
+@nx._dispatchable(edge_attrs="weight")
+def one_exchange(G, initial_cut=None, seed=None, weight=None):
+    """Compute a partitioning of the graphs nodes and the corresponding cut value.
+
+    Use a greedy one exchange strategy to find a locally maximal cut
+    and its value, it works by finding the best node (one that gives
+    the highest gain to the cut value) to add to the current cut
+    and repeats this process until no improvement can be made.
+
+    Parameters
+    ----------
+    G : networkx Graph
+        Graph to find a maximum cut for.
+
+    initial_cut : set
+        Cut to use as a starting point. If not supplied the algorithm
+        starts with an empty cut.
+
+    seed : integer, random_state, or None (default)
+        Indicator of random number generation state.
+        See :ref:`Randomness<randomness>`.
+
+    weight : object
+        Edge attribute key to use as weight. If not specified, edges
+        have weight one.
+
+    Returns
+    -------
+    cut_value : scalar
+        Value of the maximum cut.
+
+    partition : pair of node sets
+        A partitioning of the nodes that defines a maximum cut.
+
+    Examples
+    --------
+    >>> G = nx.complete_graph(5)
+    >>> curr_cut_size, partition = nx.approximation.one_exchange(G, seed=1)
+    >>> curr_cut_size
+    6
+    >>> partition
+    ({0, 2}, {1, 3, 4})
+
+    Raises
+    ------
+    NetworkXNotImplemented
+        If the graph is directed or is a multigraph.
+    """
+    if initial_cut is None:
+        initial_cut = set()
+    cut = set(initial_cut)
+    current_cut_size = nx.algorithms.cut_size(G, cut, weight=weight)
+    while True:
+        nodes = list(G.nodes())
+        # Shuffling the nodes ensures random tie-breaks in the following call to max
+        seed.shuffle(nodes)
+        best_node_to_swap = max(
+            nodes,
+            key=lambda v: nx.algorithms.cut_size(
+                G, _swap_node_partition(cut, v), weight=weight
+            ),
+            default=None,
+        )
+        potential_cut = _swap_node_partition(cut, best_node_to_swap)
+        potential_cut_size = nx.algorithms.cut_size(G, potential_cut, weight=weight)
+
+        if potential_cut_size > current_cut_size:
+            cut = potential_cut
+            current_cut_size = potential_cut_size
+        else:
+            break
+
+    partition = (cut, G.nodes - cut)
+    return current_cut_size, partition

venv/lib/python3.10/site-packages/networkx/algorithms/approximation/ramsey.py

@@ -0,0 +1,52 @@
+"""
+Ramsey numbers.
+"""
+import networkx as nx
+from networkx.utils import not_implemented_for
+
+from ...utils import arbitrary_element
+
+__all__ = ["ramsey_R2"]
+
+
+@not_implemented_for("directed")
+@not_implemented_for("multigraph")
+@nx._dispatchable
+def ramsey_R2(G):
+    r"""Compute the largest clique and largest independent set in `G`.
+
+    This can be used to estimate bounds for the 2-color
+    Ramsey number `R(2;s,t)` for `G`.
+
+    This is a recursive implementation which could run into trouble
+    for large recursions. Note that self-loop edges are ignored.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+        Undirected graph
+
+    Returns
+    -------
+    max_pair : (set, set) tuple
+        Maximum clique, Maximum independent set.
+
+    Raises
+    ------
+    NetworkXNotImplemented
+        If the graph is directed or is a multigraph.
+    """
+    if not G:
+        return set(), set()
+
+    node = arbitrary_element(G)
+    nbrs = (nbr for nbr in nx.all_neighbors(G, node) if nbr != node)
+    nnbrs = nx.non_neighbors(G, node)
+    c_1, i_1 = ramsey_R2(G.subgraph(nbrs).copy())
+    c_2, i_2 = ramsey_R2(G.subgraph(nnbrs).copy())
+
+    c_1.add(node)
+    i_2.add(node)
+    # Choose the larger of the two cliques and the larger of the two
+    # independent sets, according to cardinality.
+    return max(c_1, c_2, key=len), max(i_1, i_2, key=len)

venv/lib/python3.10/site-packages/networkx/algorithms/approximation/traveling_salesman.py

@@ -0,0 +1,1498 @@
+"""
+=================================
+Travelling Salesman Problem (TSP)
+=================================
+
+Implementation of approximate algorithms
+for solving and approximating the TSP problem.
+
+Categories of algorithms which are implemented:
+
+- Christofides (provides a 3/2-approximation of TSP)
+- Greedy
+- Simulated Annealing (SA)
+- Threshold Accepting (TA)
+- Asadpour Asymmetric Traveling Salesman Algorithm
+
+The Travelling Salesman Problem tries to find, given the weight
+(distance) between all points where a salesman has to visit, the
+route so that:
+
+- The total distance (cost) which the salesman travels is minimized.
+- The salesman returns to the starting point.
+- Note that for a complete graph, the salesman visits each point once.
+
+The function `travelling_salesman_problem` allows for incomplete
+graphs by finding all-pairs shortest paths, effectively converting
+the problem to a complete graph problem. It calls one of the
+approximate methods on that problem and then converts the result
+back to the original graph using the previously found shortest paths.
+
+TSP is an NP-hard problem in combinatorial optimization,
+important in operations research and theoretical computer science.
+
+http://en.wikipedia.org/wiki/Travelling_salesman_problem
+"""
+import math
+
+import networkx as nx
+from networkx.algorithms.tree.mst import random_spanning_tree
+from networkx.utils import not_implemented_for, pairwise, py_random_state
+
+__all__ = [
+    "traveling_salesman_problem",
+    "christofides",
+    "asadpour_atsp",
+    "greedy_tsp",
+    "simulated_annealing_tsp",
+    "threshold_accepting_tsp",
+]
+
+
+def swap_two_nodes(soln, seed):
+    """Swap two nodes in `soln` to give a neighbor solution.
+
+    Parameters
+    ----------
+    soln : list of nodes
+        Current cycle of nodes
+
+    seed : integer, random_state, or None (default)
+        Indicator of random number generation state.
+        See :ref:`Randomness<randomness>`.
+
+    Returns
+    -------
+    list
+        The solution after move is applied. (A neighbor solution.)
+
+    Notes
+    -----
+        This function assumes that the incoming list `soln` is a cycle
+        (that the first and last element are the same) and also that
+        we don't want any move to change the first node in the list
+        (and thus not the last node either).
+
+        The input list is changed as well as returned. Make a copy if needed.
+
+    See Also
+    --------
+        move_one_node
+    """
+    a, b = seed.sample(range(1, len(soln) - 1), k=2)
+    soln[a], soln[b] = soln[b], soln[a]
+    return soln
+
+
+def move_one_node(soln, seed):
+    """Move one node to another position to give a neighbor solution.
+
+    The node to move and the position to move to are chosen randomly.
+    The first and last nodes are left untouched as soln must be a cycle
+    starting at that node.
+
+    Parameters
+    ----------
+    soln : list of nodes
+        Current cycle of nodes
+
+    seed : integer, random_state, or None (default)
+        Indicator of random number generation state.
+        See :ref:`Randomness<randomness>`.
+
+    Returns
+    -------
+    list
+        The solution after move is applied. (A neighbor solution.)
+
+    Notes
+    -----
+        This function assumes that the incoming list `soln` is a cycle
+        (that the first and last element are the same) and also that
+        we don't want any move to change the first node in the list
+        (and thus not the last node either).
+
+        The input list is changed as well as returned. Make a copy if needed.
+
+    See Also
+    --------
+        swap_two_nodes
+    """
+    a, b = seed.sample(range(1, len(soln) - 1), k=2)
+    soln.insert(b, soln.pop(a))
+    return soln
+
+
+@not_implemented_for("directed")
+@nx._dispatchable(edge_attrs="weight")
+def christofides(G, weight="weight", tree=None):
+    """Approximate a solution of the traveling salesman problem
+
+    Compute a 3/2-approximation of the traveling salesman problem
+    in a complete undirected graph using Christofides [1]_ algorithm.
+
+    Parameters
+    ----------
+    G : Graph
+        `G` should be a complete weighted undirected graph.
+        The distance between all pairs of nodes should be included.
+
+    weight : string, optional (default="weight")
+        Edge data key corresponding to the edge weight.
+        If any edge does not have this attribute the weight is set to 1.
+
+    tree : NetworkX graph or None (default: None)
+        A minimum spanning tree of G. Or, if None, the minimum spanning
+        tree is computed using :func:`networkx.minimum_spanning_tree`
+
+    Returns
+    -------
+    list
+        List of nodes in `G` along a cycle with a 3/2-approximation of
+        the minimal Hamiltonian cycle.
+
+    References
+    ----------
+    .. [1] Christofides, Nicos. "Worst-case analysis of a new heuristic for
+       the travelling salesman problem." No. RR-388. Carnegie-Mellon Univ
+       Pittsburgh Pa Management Sciences Research Group, 1976.
+    """
+    # Remove selfloops if necessary
+    loop_nodes = nx.nodes_with_selfloops(G)
+    try:
+        node = next(loop_nodes)
+    except StopIteration:
+        pass
+    else:
+        G = G.copy()
+        G.remove_edge(node, node)
+        G.remove_edges_from((n, n) for n in loop_nodes)
+    # Check that G is a complete graph
+    N = len(G) - 1
+    # This check ignores selfloops which is what we want here.
+    if any(len(nbrdict) != N for n, nbrdict in G.adj.items()):
+        raise nx.NetworkXError("G must be a complete graph.")
+
+    if tree is None:
+        tree = nx.minimum_spanning_tree(G, weight=weight)
+    L = G.copy()
+    L.remove_nodes_from([v for v, degree in tree.degree if not (degree % 2)])
+    MG = nx.MultiGraph()
+    MG.add_edges_from(tree.edges)
+    edges = nx.min_weight_matching(L, weight=weight)
+    MG.add_edges_from(edges)
+    return _shortcutting(nx.eulerian_circuit(MG))
+
+
+def _shortcutting(circuit):
+    """Remove duplicate nodes in the path"""
+    nodes = []
+    for u, v in circuit:
+        if v in nodes:
+            continue
+        if not nodes:
+            nodes.append(u)
+        nodes.append(v)
+    nodes.append(nodes[0])
+    return nodes
+
+
+@nx._dispatchable(edge_attrs="weight")
+def traveling_salesman_problem(
+    G, weight="weight", nodes=None, cycle=True, method=None, **kwargs
+):
+    """Find the shortest path in `G` connecting specified nodes
+
+    This function allows approximate solution to the traveling salesman
+    problem on networks that are not complete graphs and/or where the
+    salesman does not need to visit all nodes.
+
+    This function proceeds in two steps. First, it creates a complete
+    graph using the all-pairs shortest_paths between nodes in `nodes`.
+    Edge weights in the new graph are the lengths of the paths
+    between each pair of nodes in the original graph.
+    Second, an algorithm (default: `christofides` for undirected and
+    `asadpour_atsp` for directed) is used to approximate the minimal Hamiltonian
+    cycle on this new graph. The available algorithms are:
+
+     - christofides
+     - greedy_tsp
+     - simulated_annealing_tsp
+     - threshold_accepting_tsp
+     - asadpour_atsp
+
+    Once the Hamiltonian Cycle is found, this function post-processes to
+    accommodate the structure of the original graph. If `cycle` is ``False``,
+    the biggest weight edge is removed to make a Hamiltonian path.
+    Then each edge on the new complete graph used for that analysis is
+    replaced by the shortest_path between those nodes on the original graph.
+    If the input graph `G` includes edges with weights that do not adhere to
+    the triangle inequality, such as when `G` is not a complete graph (i.e
+    length of non-existent edges is infinity), then the returned path may
+    contain some repeating nodes (other than the starting node).
+
+    Parameters
+    ----------
+    G : NetworkX graph
+        A possibly weighted graph
+
+    nodes : collection of nodes (default=G.nodes)
+        collection (list, set, etc.) of nodes to visit
+
+    weight : string, optional (default="weight")
+        Edge data key corresponding to the edge weight.
+        If any edge does not have this attribute the weight is set to 1.
+
+    cycle : bool (default: True)
+        Indicates whether a cycle should be returned, or a path.
+        Note: the cycle is the approximate minimal cycle.
+        The path simply removes the biggest edge in that cycle.
+
+    method : function (default: None)
+        A function that returns a cycle on all nodes and approximates
+        the solution to the traveling salesman problem on a complete
+        graph. The returned cycle is then used to find a corresponding
+        solution on `G`. `method` should be callable; take inputs
+        `G`, and `weight`; and return a list of nodes along the cycle.
+
+        Provided options include :func:`christofides`, :func:`greedy_tsp`,
+        :func:`simulated_annealing_tsp` and :func:`threshold_accepting_tsp`.
+
+        If `method is None`: use :func:`christofides` for undirected `G` and
+        :func:`asadpour_atsp` for directed `G`.
+
+    **kwargs : dict
+        Other keyword arguments to be passed to the `method` function passed in.
+
+    Returns
+    -------
+    list
+        List of nodes in `G` along a path with an approximation of the minimal
+        path through `nodes`.
+
+    Raises
+    ------
+    NetworkXError
+        If `G` is a directed graph it has to be strongly connected or the
+        complete version cannot be generated.
+
+    Examples
+    --------
+    >>> tsp = nx.approximation.traveling_salesman_problem
+    >>> G = nx.cycle_graph(9)
+    >>> G[4][5]["weight"] = 5  # all other weights are 1
+    >>> tsp(G, nodes=[3, 6])
+    [3, 2, 1, 0, 8, 7, 6, 7, 8, 0, 1, 2, 3]
+    >>> path = tsp(G, cycle=False)
+    >>> path in ([4, 3, 2, 1, 0, 8, 7, 6, 5], [5, 6, 7, 8, 0, 1, 2, 3, 4])
+    True
+
+    While no longer required, you can still build (curry) your own function
+    to provide parameter values to the methods.
+
+    >>> SA_tsp = nx.approximation.simulated_annealing_tsp
+    >>> method = lambda G, weight: SA_tsp(G, "greedy", weight=weight, temp=500)
+    >>> path = tsp(G, cycle=False, method=method)
+    >>> path in ([4, 3, 2, 1, 0, 8, 7, 6, 5], [5, 6, 7, 8, 0, 1, 2, 3, 4])
+    True
+
+    Otherwise, pass other keyword arguments directly into the tsp function.
+
+    >>> path = tsp(
+    ...     G,
+    ...     cycle=False,
+    ...     method=nx.approximation.simulated_annealing_tsp,
+    ...     init_cycle="greedy",
+    ...     temp=500,
+    ... )
+    >>> path in ([4, 3, 2, 1, 0, 8, 7, 6, 5], [5, 6, 7, 8, 0, 1, 2, 3, 4])
+    True
+    """
+    if method is None:
+        if G.is_directed():
+            method = asadpour_atsp
+        else:
+            method = christofides
+    if nodes is None:
+        nodes = list(G.nodes)
+
+    dist = {}
+    path = {}
+    for n, (d, p) in nx.all_pairs_dijkstra(G, weight=weight):
+        dist[n] = d
+        path[n] = p
+
+    if G.is_directed():
+        # If the graph is not strongly connected, raise an exception
+        if not nx.is_strongly_connected(G):
+            raise nx.NetworkXError("G is not strongly connected")
+        GG = nx.DiGraph()
+    else:
+        GG = nx.Graph()
+    for u in nodes:
+        for v in nodes:
+            if u == v:
+                continue
+            GG.add_edge(u, v, weight=dist[u][v])
+
+    best_GG = method(GG, weight=weight, **kwargs)
+
+    if not cycle:
+        # find and remove the biggest edge
+        (u, v) = max(pairwise(best_GG), key=lambda x: dist[x[0]][x[1]])
+        pos = best_GG.index(u) + 1
+        while best_GG[pos] != v:
+            pos = best_GG[pos:].index(u) + 1
+        best_GG = best_GG[pos:-1] + best_GG[:pos]
+
+    best_path = []
+    for u, v in pairwise(best_GG):
+        best_path.extend(path[u][v][:-1])
+    best_path.append(v)
+    return best_path
+
+
+@not_implemented_for("undirected")
+@py_random_state(2)
+@nx._dispatchable(edge_attrs="weight", mutates_input=True)
+def asadpour_atsp(G, weight="weight", seed=None, source=None):
+    """
+    Returns an approximate solution to the traveling salesman problem.
+
+    This approximate solution is one of the best known approximations for the
+    asymmetric traveling salesman problem developed by Asadpour et al,
+    [1]_. The algorithm first solves the Held-Karp relaxation to find a lower
+    bound for the weight of the cycle. Next, it constructs an exponential
+    distribution of undirected spanning trees where the probability of an
+    edge being in the tree corresponds to the weight of that edge using a
+    maximum entropy rounding scheme. Next we sample that distribution
+    $2 \\lceil \\ln n \\rceil$ times and save the minimum sampled tree once the
+    direction of the arcs is added back to the edges. Finally, we augment
+    then short circuit that graph to find the approximate tour for the
+    salesman.
+
+    Parameters
+    ----------
+    G : nx.DiGraph
+        The graph should be a complete weighted directed graph. The
+        distance between all paris of nodes should be included and the triangle
+        inequality should hold. That is, the direct edge between any two nodes
+        should be the path of least cost.
+
+    weight : string, optional (default="weight")
+        Edge data key corresponding to the edge weight.
+        If any edge does not have this attribute the weight is set to 1.
+
+    seed : integer, random_state, or None (default)
+        Indicator of random number generation state.
+        See :ref:`Randomness<randomness>`.
+
+    source : node label (default=`None`)
+        If given, return the cycle starting and ending at the given node.
+
+    Returns
+    -------
+    cycle : list of nodes
+        Returns the cycle (list of nodes) that a salesman can follow to minimize
+        the total weight of the trip.
+
+    Raises
+    ------
+    NetworkXError
+        If `G` is not complete or has less than two nodes, the algorithm raises
+        an exception.
+
+    NetworkXError
+        If `source` is not `None` and is not a node in `G`, the algorithm raises
+        an exception.
+
+    NetworkXNotImplemented
+        If `G` is an undirected graph.
+
+    References
+    ----------
+    .. [1] A. Asadpour, M. X. Goemans, A. Madry, S. O. Gharan, and A. Saberi,
+       An o(log n/log log n)-approximation algorithm for the asymmetric
+       traveling salesman problem, Operations research, 65 (2017),
+       pp. 1043–1061
+
+    Examples
+    --------
+    >>> import networkx as nx
+    >>> import networkx.algorithms.approximation as approx
+    >>> G = nx.complete_graph(3, create_using=nx.DiGraph)
+    >>> nx.set_edge_attributes(
+    ...     G, {(0, 1): 2, (1, 2): 2, (2, 0): 2, (0, 2): 1, (2, 1): 1, (1, 0): 1}, "weight"
+    ... )
+    >>> tour = approx.asadpour_atsp(G, source=0)
+    >>> tour
+    [0, 2, 1, 0]
+    """
+    from math import ceil, exp
+    from math import log as ln
+
+    # Check that G is a complete graph
+    N = len(G) - 1
+    if N < 2:
+        raise nx.NetworkXError("G must have at least two nodes")
+    # This check ignores selfloops which is what we want here.
+    if any(len(nbrdict) - (n in nbrdict) != N for n, nbrdict in G.adj.items()):
+        raise nx.NetworkXError("G is not a complete DiGraph")
+    # Check that the source vertex, if given, is in the graph
+    if source is not None and source not in G.nodes:
+        raise nx.NetworkXError("Given source node not in G.")
+
+    opt_hk, z_star = held_karp_ascent(G, weight)
+
+    # Test to see if the ascent method found an integer solution or a fractional
+    # solution. If it is integral then z_star is a nx.Graph, otherwise it is
+    # a dict
+    if not isinstance(z_star, dict):
+        # Here we are using the shortcutting method to go from the list of edges
+        # returned from eulerian_circuit to a list of nodes
+        return _shortcutting(nx.eulerian_circuit(z_star, source=source))
+
+    # Create the undirected support of z_star
+    z_support = nx.MultiGraph()
+    for u, v in z_star:
+        if (u, v) not in z_support.edges:
+            edge_weight = min(G[u][v][weight], G[v][u][weight])
+            z_support.add_edge(u, v, **{weight: edge_weight})
+
+    # Create the exponential distribution of spanning trees
+    gamma = spanning_tree_distribution(z_support, z_star)
+
+    # Write the lambda values to the edges of z_support
+    z_support = nx.Graph(z_support)
+    lambda_dict = {(u, v): exp(gamma[(u, v)]) for u, v in z_support.edges()}
+    nx.set_edge_attributes(z_support, lambda_dict, "weight")
+    del gamma, lambda_dict
+
+    # Sample 2 * ceil( ln(n) ) spanning trees and record the minimum one
+    minimum_sampled_tree = None
+    minimum_sampled_tree_weight = math.inf
+    for _ in range(2 * ceil(ln(G.number_of_nodes()))):
+        sampled_tree = random_spanning_tree(z_support, "weight", seed=seed)
+        sampled_tree_weight = sampled_tree.size(weight)
+        if sampled_tree_weight < minimum_sampled_tree_weight:
+            minimum_sampled_tree = sampled_tree.copy()
+            minimum_sampled_tree_weight = sampled_tree_weight
+
+    # Orient the edges in that tree to keep the cost of the tree the same.
+    t_star = nx.MultiDiGraph()
+    for u, v, d in minimum_sampled_tree.edges(data=weight):
+        if d == G[u][v][weight]:
+            t_star.add_edge(u, v, **{weight: d})
+        else:
+            t_star.add_edge(v, u, **{weight: d})
+
+    # Find the node demands needed to neutralize the flow of t_star in G
+    node_demands = {n: t_star.out_degree(n) - t_star.in_degree(n) for n in t_star}
+    nx.set_node_attributes(G, node_demands, "demand")
+
+    # Find the min_cost_flow
+    flow_dict = nx.min_cost_flow(G, "demand")
+
+    # Build the flow into t_star
+    for source, values in flow_dict.items():
+        for target in values:
+            if (source, target) not in t_star.edges and values[target] > 0:
+                # IF values[target] > 0 we have to add that many edges
+                for _ in range(values[target]):
+                    t_star.add_edge(source, target)
+
+    # Return the shortcut eulerian circuit
+    circuit = nx.eulerian_circuit(t_star, source=source)
+    return _shortcutting(circuit)
+
+
+@nx._dispatchable(edge_attrs="weight", mutates_input=True, returns_graph=True)
+def held_karp_ascent(G, weight="weight"):
+    """
+    Minimizes the Held-Karp relaxation of the TSP for `G`
+
+    Solves the Held-Karp relaxation of the input complete digraph and scales
+    the output solution for use in the Asadpour [1]_ ASTP algorithm.
+
+    The Held-Karp relaxation defines the lower bound for solutions to the
+    ATSP, although it does return a fractional solution. This is used in the
+    Asadpour algorithm as an initial solution which is later rounded to a
+    integral tree within the spanning tree polytopes. This function solves
+    the relaxation with the branch and bound method in [2]_.
+
+    Parameters
+    ----------
+    G : nx.DiGraph
+        The graph should be a complete weighted directed graph.
+        The distance between all paris of nodes should be included.
+
+    weight : string, optional (default="weight")
+        Edge data key corresponding to the edge weight.
+        If any edge does not have this attribute the weight is set to 1.
+
+    Returns
+    -------
+    OPT : float
+        The cost for the optimal solution to the Held-Karp relaxation
+    z : dict or nx.Graph
+        A symmetrized and scaled version of the optimal solution to the
+        Held-Karp relaxation for use in the Asadpour algorithm.
+
+        If an integral solution is found, then that is an optimal solution for
+        the ATSP problem and that is returned instead.
+
+    References
+    ----------
+    .. [1] A. Asadpour, M. X. Goemans, A. Madry, S. O. Gharan, and A. Saberi,
+       An o(log n/log log n)-approximation algorithm for the asymmetric
+       traveling salesman problem, Operations research, 65 (2017),
+       pp. 1043–1061
+
+    .. [2] M. Held, R. M. Karp, The traveling-salesman problem and minimum
+           spanning trees, Operations Research, 1970-11-01, Vol. 18 (6),
+           pp.1138-1162
+    """
+    import numpy as np
+    from scipy import optimize
+
+    def k_pi():
+        """
+        Find the set of minimum 1-Arborescences for G at point pi.
+
+        Returns
+        -------
+        Set
+            The set of minimum 1-Arborescences
+        """
+        # Create a copy of G without vertex 1.
+        G_1 = G.copy()
+        minimum_1_arborescences = set()
+        minimum_1_arborescence_weight = math.inf
+
+        # node is node '1' in the Held and Karp paper
+        n = next(G.__iter__())
+        G_1.remove_node(n)
+
+        # Iterate over the spanning arborescences of the graph until we know
+        # that we have found the minimum 1-arborescences. My proposed strategy
+        # is to find the most extensive root to connect to from 'node 1' and
+        # the least expensive one. We then iterate over arborescences until
+        # the cost of the basic arborescence is the cost of the minimum one
+        # plus the difference between the most and least expensive roots,
+        # that way the cost of connecting 'node 1' will by definition not by
+        # minimum
+        min_root = {"node": None, weight: math.inf}
+        max_root = {"node": None, weight: -math.inf}
+        for u, v, d in G.edges(n, data=True):
+            if d[weight] < min_root[weight]:
+                min_root = {"node": v, weight: d[weight]}
+            if d[weight] > max_root[weight]:
+                max_root = {"node": v, weight: d[weight]}
+
+        min_in_edge = min(G.in_edges(n, data=True), key=lambda x: x[2][weight])
+        min_root[weight] = min_root[weight] + min_in_edge[2][weight]
+        max_root[weight] = max_root[weight] + min_in_edge[2][weight]
+
+        min_arb_weight = math.inf
+        for arb in nx.ArborescenceIterator(G_1):
+            arb_weight = arb.size(weight)
+            if min_arb_weight == math.inf:
+                min_arb_weight = arb_weight
+            elif arb_weight > min_arb_weight + max_root[weight] - min_root[weight]:
+                break
+            # We have to pick the root node of the arborescence for the out
+            # edge of the first vertex as that is the only node without an
+            # edge directed into it.
+            for N, deg in arb.in_degree:
+                if deg == 0:
+                    # root found
+                    arb.add_edge(n, N, **{weight: G[n][N][weight]})
+                    arb_weight += G[n][N][weight]
+                    break
+
+            # We can pick the minimum weight in-edge for the vertex with
+            # a cycle. If there are multiple edges with the same, minimum
+            # weight, We need to add all of them.
+            #
+            # Delete the edge (N, v) so that we cannot pick it.
+            edge_data = G[N][n]
+            G.remove_edge(N, n)
+            min_weight = min(G.in_edges(n, data=weight), key=lambda x: x[2])[2]
+            min_edges = [
+                (u, v, d) for u, v, d in G.in_edges(n, data=weight) if d == min_weight
+            ]
+            for u, v, d in min_edges:
+                new_arb = arb.copy()
+                new_arb.add_edge(u, v, **{weight: d})
+                new_arb_weight = arb_weight + d
+                # Check to see the weight of the arborescence, if it is a
+                # new minimum, clear all of the old potential minimum
+                # 1-arborescences and add this is the only one. If its
+                # weight is above the known minimum, do not add it.
+                if new_arb_weight < minimum_1_arborescence_weight:
+                    minimum_1_arborescences.clear()
+                    minimum_1_arborescence_weight = new_arb_weight
+                # We have a 1-arborescence, add it to the set
+                if new_arb_weight == minimum_1_arborescence_weight:
+                    minimum_1_arborescences.add(new_arb)
+            G.add_edge(N, n, **edge_data)
+
+        return minimum_1_arborescences
+
+    def direction_of_ascent():
+        """
+        Find the direction of ascent at point pi.
+
+        See [1]_ for more information.
+
+        Returns
+        -------
+        dict
+            A mapping from the nodes of the graph which represents the direction
+            of ascent.
+
+        References
+        ----------
+        .. [1] M. Held, R. M. Karp, The traveling-salesman problem and minimum
+           spanning trees, Operations Research, 1970-11-01, Vol. 18 (6),
+           pp.1138-1162
+        """
+        # 1. Set d equal to the zero n-vector.
+        d = {}
+        for n in G:
+            d[n] = 0
+        del n
+        # 2. Find a 1-Arborescence T^k such that k is in K(pi, d).
+        minimum_1_arborescences = k_pi()
+        while True:
+            # Reduce K(pi) to K(pi, d)
+            # Find the arborescence in K(pi) which increases the lest in
+            # direction d
+            min_k_d_weight = math.inf
+            min_k_d = None
+            for arborescence in minimum_1_arborescences:
+                weighted_cost = 0
+                for n, deg in arborescence.degree:
+                    weighted_cost += d[n] * (deg - 2)
+                if weighted_cost < min_k_d_weight:
+                    min_k_d_weight = weighted_cost
+                    min_k_d = arborescence
+
+            # 3. If sum of d_i * v_{i, k} is greater than zero, terminate
+            if min_k_d_weight > 0:
+                return d, min_k_d
+            # 4. d_i = d_i + v_{i, k}
+            for n, deg in min_k_d.degree:
+                d[n] += deg - 2
+            # Check that we do not need to terminate because the direction
+            # of ascent does not exist. This is done with linear
+            # programming.
+            c = np.full(len(minimum_1_arborescences), -1, dtype=int)
+            a_eq = np.empty((len(G) + 1, len(minimum_1_arborescences)), dtype=int)
+            b_eq = np.zeros(len(G) + 1, dtype=int)
+            b_eq[len(G)] = 1
+            for arb_count, arborescence in enumerate(minimum_1_arborescences):
+                n_count = len(G) - 1
+                for n, deg in arborescence.degree:
+                    a_eq[n_count][arb_count] = deg - 2
+                    n_count -= 1
+                a_eq[len(G)][arb_count] = 1
+            program_result = optimize.linprog(
+                c, A_eq=a_eq, b_eq=b_eq, method="highs-ipm"
+            )
+            # If the constants exist, then the direction of ascent doesn't
+            if program_result.success:
+                # There is no direction of ascent
+                return None, minimum_1_arborescences
+
+            # 5. GO TO 2
+
+    def find_epsilon(k, d):
+        """
+        Given the direction of ascent at pi, find the maximum distance we can go
+        in that direction.
+
+        Parameters
+        ----------
+        k_xy : set
+            The set of 1-arborescences which have the minimum rate of increase
+            in the direction of ascent
+
+        d : dict
+            The direction of ascent
+
+        Returns
+        -------
+        float
+            The distance we can travel in direction `d`
+        """
+        min_epsilon = math.inf
+        for e_u, e_v, e_w in G.edges(data=weight):
+            if (e_u, e_v) in k.edges:
+                continue
+            # Now, I have found a condition which MUST be true for the edges to
+            # be a valid substitute. The edge in the graph which is the
+            # substitute is the one with the same terminated end. This can be
+            # checked rather simply.
+            #
+            # Find the edge within k which is the substitute. Because k is a
+            # 1-arborescence, we know that they is only one such edges
+            # leading into every vertex.
+            if len(k.in_edges(e_v, data=weight)) > 1:
+                raise Exception
+            sub_u, sub_v, sub_w = next(k.in_edges(e_v, data=weight).__iter__())
+            k.add_edge(e_u, e_v, **{weight: e_w})
+            k.remove_edge(sub_u, sub_v)
+            if (
+                max(d for n, d in k.in_degree()) <= 1
+                and len(G) == k.number_of_edges()
+                and nx.is_weakly_connected(k)
+            ):
+                # Ascent method calculation
+                if d[sub_u] == d[e_u] or sub_w == e_w:
+                    # Revert to the original graph
+                    k.remove_edge(e_u, e_v)
+                    k.add_edge(sub_u, sub_v, **{weight: sub_w})
+                    continue
+                epsilon = (sub_w - e_w) / (d[e_u] - d[sub_u])
+                if 0 < epsilon < min_epsilon:
+                    min_epsilon = epsilon
+            # Revert to the original graph
+            k.remove_edge(e_u, e_v)
+            k.add_edge(sub_u, sub_v, **{weight: sub_w})
+
+        return min_epsilon
+
+    # I have to know that the elements in pi correspond to the correct elements
+    # in the direction of ascent, even if the node labels are not integers.
+    # Thus, I will use dictionaries to made that mapping.
+    pi_dict = {}
+    for n in G:
+        pi_dict[n] = 0
+    del n
+    original_edge_weights = {}
+    for u, v, d in G.edges(data=True):
+        original_edge_weights[(u, v)] = d[weight]
+    dir_ascent, k_d = direction_of_ascent()
+    while dir_ascent is not None:
+        max_distance = find_epsilon(k_d, dir_ascent)
+        for n, v in dir_ascent.items():
+            pi_dict[n] += max_distance * v
+        for u, v, d in G.edges(data=True):
+            d[weight] = original_edge_weights[(u, v)] + pi_dict[u]
+        dir_ascent, k_d = direction_of_ascent()
+    nx._clear_cache(G)
+    # k_d is no longer an individual 1-arborescence but rather a set of
+    # minimal 1-arborescences at the maximum point of the polytope and should
+    # be reflected as such
+    k_max = k_d
+
+    # Search for a cycle within k_max. If a cycle exists, return it as the
+    # solution
+    for k in k_max:
+        if len([n for n in k if k.degree(n) == 2]) == G.order():
+            # Tour found
+            # TODO: this branch does not restore original_edge_weights of G!
+            return k.size(weight), k
+
+    # Write the original edge weights back to G and every member of k_max at
+    # the maximum point. Also average the number of times that edge appears in
+    # the set of minimal 1-arborescences.
+    x_star = {}
+    size_k_max = len(k_max)
+    for u, v, d in G.edges(data=True):
+        edge_count = 0
+        d[weight] = original_edge_weights[(u, v)]
+        for k in k_max:
+            if (u, v) in k.edges():
+                edge_count += 1
+                k[u][v][weight] = original_edge_weights[(u, v)]
+        x_star[(u, v)] = edge_count / size_k_max
+    # Now symmetrize the edges in x_star and scale them according to (5) in
+    # reference [1]
+    z_star = {}
+    scale_factor = (G.order() - 1) / G.order()
+    for u, v in x_star:
+        frequency = x_star[(u, v)] + x_star[(v, u)]
+        if frequency > 0:
+            z_star[(u, v)] = scale_factor * frequency
+    del x_star
+    # Return the optimal weight and the z dict
+    return next(k_max.__iter__()).size(weight), z_star
+
+
+@nx._dispatchable
+def spanning_tree_distribution(G, z):
+    """
+    Find the asadpour exponential distribution of spanning trees.
+
+    Solves the Maximum Entropy Convex Program in the Asadpour algorithm [1]_
+    using the approach in section 7 to build an exponential distribution of
+    undirected spanning trees.
+
+    This algorithm ensures that the probability of any edge in a spanning
+    tree is proportional to the sum of the probabilities of the tress
+    containing that edge over the sum of the probabilities of all spanning
+    trees of the graph.
+
+    Parameters
+    ----------
+    G : nx.MultiGraph
+        The undirected support graph for the Held Karp relaxation
+
+    z : dict
+        The output of `held_karp_ascent()`, a scaled version of the Held-Karp
+        solution.
+
+    Returns
+    -------
+    gamma : dict
+        The probability distribution which approximately preserves the marginal
+        probabilities of `z`.
+    """
+    from math import exp
+    from math import log as ln
+
+    def q(e):
+        """
+        The value of q(e) is described in the Asadpour paper is "the
+        probability that edge e will be included in a spanning tree T that is
+        chosen with probability proportional to exp(gamma(T))" which
+        basically means that it is the total probability of the edge appearing
+        across the whole distribution.
+
+        Parameters
+        ----------
+        e : tuple
+            The `(u, v)` tuple describing the edge we are interested in
+
+        Returns
+        -------
+        float
+            The probability that a spanning tree chosen according to the
+            current values of gamma will include edge `e`.
+        """
+        # Create the laplacian matrices
+        for u, v, d in G.edges(data=True):
+            d[lambda_key] = exp(gamma[(u, v)])
+        G_Kirchhoff = nx.total_spanning_tree_weight(G, lambda_key)
+        G_e = nx.contracted_edge(G, e, self_loops=False)
+        G_e_Kirchhoff = nx.total_spanning_tree_weight(G_e, lambda_key)
+
+        # Multiply by the weight of the contracted edge since it is not included
+        # in the total weight of the contracted graph.
+        return exp(gamma[(e[0], e[1])]) * G_e_Kirchhoff / G_Kirchhoff
+
+    # initialize gamma to the zero dict
+    gamma = {}
+    for u, v, _ in G.edges:
+        gamma[(u, v)] = 0
+
+    # set epsilon
+    EPSILON = 0.2
+
+    # pick an edge attribute name that is unlikely to be in the graph
+    lambda_key = "spanning_tree_distribution's secret attribute name for lambda"
+
+    while True:
+        # We need to know that know that no values of q_e are greater than
+        # (1 + epsilon) * z_e, however changing one gamma value can increase the
+        # value of a different q_e, so we have to complete the for loop without
+        # changing anything for the condition to be meet
+        in_range_count = 0
+        # Search for an edge with q_e > (1 + epsilon) * z_e
+        for u, v in gamma:
+            e = (u, v)
+            q_e = q(e)
+            z_e = z[e]
+            if q_e > (1 + EPSILON) * z_e:
+                delta = ln(
+                    (q_e * (1 - (1 + EPSILON / 2) * z_e))
+                    / ((1 - q_e) * (1 + EPSILON / 2) * z_e)
+                )
+                gamma[e] -= delta
+                # Check that delta had the desired effect
+                new_q_e = q(e)
+                desired_q_e = (1 + EPSILON / 2) * z_e
+                if round(new_q_e, 8) != round(desired_q_e, 8):
+                    raise nx.NetworkXError(
+                        f"Unable to modify probability for edge ({u}, {v})"
+                    )
+            else:
+                in_range_count += 1
+        # Check if the for loop terminated without changing any gamma
+        if in_range_count == len(gamma):
+            break
+
+    # Remove the new edge attributes
+    for _, _, d in G.edges(data=True):
+        if lambda_key in d:
+            del d[lambda_key]
+
+    return gamma
+
+
+@nx._dispatchable(edge_attrs="weight")
+def greedy_tsp(G, weight="weight", source=None):
+    """Return a low cost cycle starting at `source` and its cost.
+
+    This approximates a solution to the traveling salesman problem.
+    It finds a cycle of all the nodes that a salesman can visit in order
+    to visit many nodes while minimizing total distance.
+    It uses a simple greedy algorithm.
+    In essence, this function returns a large cycle given a source point
+    for which the total cost of the cycle is minimized.
+
+    Parameters
+    ----------
+    G : Graph
+        The Graph should be a complete weighted undirected graph.
+        The distance between all pairs of nodes should be included.
+
+    weight : string, optional (default="weight")
+        Edge data key corresponding to the edge weight.
+        If any edge does not have this attribute the weight is set to 1.
+
+    source : node, optional (default: first node in list(G))
+        Starting node.  If None, defaults to ``next(iter(G))``
+
+    Returns
+    -------
+    cycle : list of nodes
+        Returns the cycle (list of nodes) that a salesman
+        can follow to minimize total weight of the trip.
+
+    Raises
+    ------
+    NetworkXError
+        If `G` is not complete, the algorithm raises an exception.
+
+    Examples
+    --------
+    >>> from networkx.algorithms import approximation as approx
+    >>> G = nx.DiGraph()
+    >>> G.add_weighted_edges_from(
+    ...     {
+    ...         ("A", "B", 3),
+    ...         ("A", "C", 17),
+    ...         ("A", "D", 14),
+    ...         ("B", "A", 3),
+    ...         ("B", "C", 12),
+    ...         ("B", "D", 16),
+    ...         ("C", "A", 13),
+    ...         ("C", "B", 12),
+    ...         ("C", "D", 4),
+    ...         ("D", "A", 14),
+    ...         ("D", "B", 15),
+    ...         ("D", "C", 2),
+    ...     }
+    ... )
+    >>> cycle = approx.greedy_tsp(G, source="D")
+    >>> cost = sum(G[n][nbr]["weight"] for n, nbr in nx.utils.pairwise(cycle))
+    >>> cycle
+    ['D', 'C', 'B', 'A', 'D']
+    >>> cost
+    31
+
+    Notes
+    -----
+    This implementation of a greedy algorithm is based on the following:
+
+    - The algorithm adds a node to the solution at every iteration.
+    - The algorithm selects a node not already in the cycle whose connection
+      to the previous node adds the least cost to the cycle.
+
+    A greedy algorithm does not always give the best solution.
+    However, it can construct a first feasible solution which can
+    be passed as a parameter to an iterative improvement algorithm such
+    as Simulated Annealing, or Threshold Accepting.
+
+    Time complexity: It has a running time $O(|V|^2)$
+    """
+    # Check that G is a complete graph
+    N = len(G) - 1
+    # This check ignores selfloops which is what we want here.
+    if any(len(nbrdict) - (n in nbrdict) != N for n, nbrdict in G.adj.items()):
+        raise nx.NetworkXError("G must be a complete graph.")
+
+    if source is None:
+        source = nx.utils.arbitrary_element(G)
+
+    if G.number_of_nodes() == 2:
+        neighbor = next(G.neighbors(source))
+        return [source, neighbor, source]
+
+    nodeset = set(G)
+    nodeset.remove(source)
+    cycle = [source]
+    next_node = source
+    while nodeset:
+        nbrdict = G[next_node]
+        next_node = min(nodeset, key=lambda n: nbrdict[n].get(weight, 1))
+        cycle.append(next_node)
+        nodeset.remove(next_node)
+    cycle.append(cycle[0])
+    return cycle
+
+
+@py_random_state(9)
+@nx._dispatchable(edge_attrs="weight")
+def simulated_annealing_tsp(
+    G,
+    init_cycle,
+    weight="weight",
+    source=None,
+    temp=100,
+    move="1-1",
+    max_iterations=10,
+    N_inner=100,
+    alpha=0.01,
+    seed=None,
+):
+    """Returns an approximate solution to the traveling salesman problem.
+
+    This function uses simulated annealing to approximate the minimal cost
+    cycle through the nodes. Starting from a suboptimal solution, simulated
+    annealing perturbs that solution, occasionally accepting changes that make
+    the solution worse to escape from a locally optimal solution. The chance
+    of accepting such changes decreases over the iterations to encourage
+    an optimal result.  In summary, the function returns a cycle starting
+    at `source` for which the total cost is minimized. It also returns the cost.
+
+    The chance of accepting a proposed change is related to a parameter called
+    the temperature (annealing has a physical analogue of steel hardening
+    as it cools). As the temperature is reduced, the chance of moves that
+    increase cost goes down.
+
+    Parameters
+    ----------
+    G : Graph
+        `G` should be a complete weighted graph.
+        The distance between all pairs of nodes should be included.
+
+    init_cycle : list of all nodes or "greedy"
+        The initial solution (a cycle through all nodes returning to the start).
+        This argument has no default to make you think about it.
+        If "greedy", use `greedy_tsp(G, weight)`.
+        Other common starting cycles are `list(G) + [next(iter(G))]` or the final
+        result of `simulated_annealing_tsp` when doing `threshold_accepting_tsp`.
+
+    weight : string, optional (default="weight")
+        Edge data key corresponding to the edge weight.
+        If any edge does not have this attribute the weight is set to 1.
+
+    source : node, optional (default: first node in list(G))
+        Starting node.  If None, defaults to ``next(iter(G))``
+
+    temp : int, optional (default=100)
+        The algorithm's temperature parameter. It represents the initial
+        value of temperature
+
+    move : "1-1" or "1-0" or function, optional (default="1-1")
+        Indicator of what move to use when finding new trial solutions.
+        Strings indicate two special built-in moves:
+
+        - "1-1": 1-1 exchange which transposes the position
+          of two elements of the current solution.
+          The function called is :func:`swap_two_nodes`.
+          For example if we apply 1-1 exchange in the solution
+          ``A = [3, 2, 1, 4, 3]``
+          we can get the following by the transposition of 1 and 4 elements:
+          ``A' = [3, 2, 4, 1, 3]``
+        - "1-0": 1-0 exchange which moves an node in the solution
+          to a new position.
+          The function called is :func:`move_one_node`.
+          For example if we apply 1-0 exchange in the solution
+          ``A = [3, 2, 1, 4, 3]``
+          we can transfer the fourth element to the second position:
+          ``A' = [3, 4, 2, 1, 3]``
+
+        You may provide your own functions to enact a move from
+        one solution to a neighbor solution. The function must take
+        the solution as input along with a `seed` input to control
+        random number generation (see the `seed` input here).
+        Your function should maintain the solution as a cycle with
+        equal first and last node and all others appearing once.
+        Your function should return the new solution.
+
+    max_iterations : int, optional (default=10)
+        Declared done when this number of consecutive iterations of
+        the outer loop occurs without any change in the best cost solution.
+
+    N_inner : int, optional (default=100)
+        The number of iterations of the inner loop.
+
+    alpha : float between (0, 1), optional (default=0.01)
+        Percentage of temperature decrease in each iteration
+        of outer loop
+
+    seed : integer, random_state, or None (default)
+        Indicator of random number generation state.
+        See :ref:`Randomness<randomness>`.
+
+    Returns
+    -------
+    cycle : list of nodes
+        Returns the cycle (list of nodes) that a salesman
+        can follow to minimize total weight of the trip.
+
+    Raises
+    ------
+    NetworkXError
+        If `G` is not complete the algorithm raises an exception.
+
+    Examples
+    --------
+    >>> from networkx.algorithms import approximation as approx
+    >>> G = nx.DiGraph()
+    >>> G.add_weighted_edges_from(
+    ...     {
+    ...         ("A", "B", 3),
+    ...         ("A", "C", 17),
+    ...         ("A", "D", 14),
+    ...         ("B", "A", 3),
+    ...         ("B", "C", 12),
+    ...         ("B", "D", 16),
+    ...         ("C", "A", 13),
+    ...         ("C", "B", 12),
+    ...         ("C", "D", 4),
+    ...         ("D", "A", 14),
+    ...         ("D", "B", 15),
+    ...         ("D", "C", 2),
+    ...     }
+    ... )
+    >>> cycle = approx.simulated_annealing_tsp(G, "greedy", source="D")
+    >>> cost = sum(G[n][nbr]["weight"] for n, nbr in nx.utils.pairwise(cycle))
+    >>> cycle
+    ['D', 'C', 'B', 'A', 'D']
+    >>> cost
+    31
+    >>> incycle = ["D", "B", "A", "C", "D"]
+    >>> cycle = approx.simulated_annealing_tsp(G, incycle, source="D")
+    >>> cost = sum(G[n][nbr]["weight"] for n, nbr in nx.utils.pairwise(cycle))
+    >>> cycle
+    ['D', 'C', 'B', 'A', 'D']
+    >>> cost
+    31
+
+    Notes
+    -----
+    Simulated Annealing is a metaheuristic local search algorithm.
+    The main characteristic of this algorithm is that it accepts
+    even solutions which lead to the increase of the cost in order
+    to escape from low quality local optimal solutions.
+
+    This algorithm needs an initial solution. If not provided, it is
+    constructed by a simple greedy algorithm. At every iteration, the
+    algorithm selects thoughtfully a neighbor solution.
+    Consider $c(x)$ cost of current solution and $c(x')$ cost of a
+    neighbor solution.
+    If $c(x') - c(x) <= 0$ then the neighbor solution becomes the current
+    solution for the next iteration. Otherwise, the algorithm accepts
+    the neighbor solution with probability $p = exp - ([c(x') - c(x)] / temp)$.
+    Otherwise the current solution is retained.
+
+    `temp` is a parameter of the algorithm and represents temperature.
+
+    Time complexity:
+    For $N_i$ iterations of the inner loop and $N_o$ iterations of the
+    outer loop, this algorithm has running time $O(N_i * N_o * |V|)$.
+
+    For more information and how the algorithm is inspired see:
+    http://en.wikipedia.org/wiki/Simulated_annealing
+    """
+    if move == "1-1":
+        move = swap_two_nodes
+    elif move == "1-0":
+        move = move_one_node
+    if init_cycle == "greedy":
+        # Construct an initial solution using a greedy algorithm.
+        cycle = greedy_tsp(G, weight=weight, source=source)
+        if G.number_of_nodes() == 2:
+            return cycle
+
+    else:
+        cycle = list(init_cycle)
+        if source is None:
+            source = cycle[0]
+        elif source != cycle[0]:
+            raise nx.NetworkXError("source must be first node in init_cycle")
+        if cycle[0] != cycle[-1]:
+            raise nx.NetworkXError("init_cycle must be a cycle. (return to start)")
+
+        if len(cycle) - 1 != len(G) or len(set(G.nbunch_iter(cycle))) != len(G):
+            raise nx.NetworkXError("init_cycle should be a cycle over all nodes in G.")
+
+        # Check that G is a complete graph
+        N = len(G) - 1
+        # This check ignores selfloops which is what we want here.
+        if any(len(nbrdict) - (n in nbrdict) != N for n, nbrdict in G.adj.items()):
+            raise nx.NetworkXError("G must be a complete graph.")
+
+        if G.number_of_nodes() == 2:
+            neighbor = next(G.neighbors(source))
+            return [source, neighbor, source]
+
+    # Find the cost of initial solution
+    cost = sum(G[u][v].get(weight, 1) for u, v in pairwise(cycle))
+
+    count = 0
+    best_cycle = cycle.copy()
+    best_cost = cost
+    while count <= max_iterations and temp > 0:
+        count += 1
+        for i in range(N_inner):
+            adj_sol = move(cycle, seed)
+            adj_cost = sum(G[u][v].get(weight, 1) for u, v in pairwise(adj_sol))
+            delta = adj_cost - cost
+            if delta <= 0:
+                # Set current solution the adjacent solution.
+                cycle = adj_sol
+                cost = adj_cost
+
+                if cost < best_cost:
+                    count = 0
+                    best_cycle = cycle.copy()
+                    best_cost = cost
+            else:
+                # Accept even a worse solution with probability p.
+                p = math.exp(-delta / temp)
+                if p >= seed.random():
+                    cycle = adj_sol
+                    cost = adj_cost
+        temp -= temp * alpha
+
+    return best_cycle
+
+
+@py_random_state(9)
+@nx._dispatchable(edge_attrs="weight")
+def threshold_accepting_tsp(
+    G,
+    init_cycle,
+    weight="weight",
+    source=None,
+    threshold=1,
+    move="1-1",
+    max_iterations=10,
+    N_inner=100,
+    alpha=0.1,
+    seed=None,
+):
+    """Returns an approximate solution to the traveling salesman problem.
+
+    This function uses threshold accepting methods to approximate the minimal cost
+    cycle through the nodes. Starting from a suboptimal solution, threshold
+    accepting methods perturb that solution, accepting any changes that make
+    the solution no worse than increasing by a threshold amount. Improvements
+    in cost are accepted, but so are changes leading to small increases in cost.
+    This allows the solution to leave suboptimal local minima in solution space.
+    The threshold is decreased slowly as iterations proceed helping to ensure
+    an optimum. In summary, the function returns a cycle starting at `source`
+    for which the total cost is minimized.
+
+    Parameters
+    ----------
+    G : Graph
+        `G` should be a complete weighted graph.
+        The distance between all pairs of nodes should be included.
+
+    init_cycle : list or "greedy"
+        The initial solution (a cycle through all nodes returning to the start).
+        This argument has no default to make you think about it.
+        If "greedy", use `greedy_tsp(G, weight)`.
+        Other common starting cycles are `list(G) + [next(iter(G))]` or the final
+        result of `simulated_annealing_tsp` when doing `threshold_accepting_tsp`.
+
+    weight : string, optional (default="weight")
+        Edge data key corresponding to the edge weight.
+        If any edge does not have this attribute the weight is set to 1.
+
+    source : node, optional (default: first node in list(G))
+        Starting node.  If None, defaults to ``next(iter(G))``
+
+    threshold : int, optional (default=1)
+        The algorithm's threshold parameter. It represents the initial
+        threshold's value
+
+    move : "1-1" or "1-0" or function, optional (default="1-1")
+        Indicator of what move to use when finding new trial solutions.
+        Strings indicate two special built-in moves:
+
+        - "1-1": 1-1 exchange which transposes the position
+          of two elements of the current solution.
+          The function called is :func:`swap_two_nodes`.
+          For example if we apply 1-1 exchange in the solution
+          ``A = [3, 2, 1, 4, 3]``
+          we can get the following by the transposition of 1 and 4 elements:
+          ``A' = [3, 2, 4, 1, 3]``
+        - "1-0": 1-0 exchange which moves an node in the solution
+          to a new position.
+          The function called is :func:`move_one_node`.
+          For example if we apply 1-0 exchange in the solution
+          ``A = [3, 2, 1, 4, 3]``
+          we can transfer the fourth element to the second position:
+          ``A' = [3, 4, 2, 1, 3]``
+
+        You may provide your own functions to enact a move from
+        one solution to a neighbor solution. The function must take
+        the solution as input along with a `seed` input to control
+        random number generation (see the `seed` input here).
+        Your function should maintain the solution as a cycle with
+        equal first and last node and all others appearing once.
+        Your function should return the new solution.
+
+    max_iterations : int, optional (default=10)
+        Declared done when this number of consecutive iterations of
+        the outer loop occurs without any change in the best cost solution.
+
+    N_inner : int, optional (default=100)
+        The number of iterations of the inner loop.
+
+    alpha : float between (0, 1), optional (default=0.1)
+        Percentage of threshold decrease when there is at
+        least one acceptance of a neighbor solution.
+        If no inner loop moves are accepted the threshold remains unchanged.
+
+    seed : integer, random_state, or None (default)
+        Indicator of random number generation state.
+        See :ref:`Randomness<randomness>`.
+
+    Returns
+    -------
+    cycle : list of nodes
+        Returns the cycle (list of nodes) that a salesman
+        can follow to minimize total weight of the trip.
+
+    Raises
+    ------
+    NetworkXError
+        If `G` is not complete the algorithm raises an exception.
+
+    Examples
+    --------
+    >>> from networkx.algorithms import approximation as approx
+    >>> G = nx.DiGraph()
+    >>> G.add_weighted_edges_from(
+    ...     {
+    ...         ("A", "B", 3),
+    ...         ("A", "C", 17),
+    ...         ("A", "D", 14),
+    ...         ("B", "A", 3),
+    ...         ("B", "C", 12),
+    ...         ("B", "D", 16),
+    ...         ("C", "A", 13),
+    ...         ("C", "B", 12),
+    ...         ("C", "D", 4),
+    ...         ("D", "A", 14),
+    ...         ("D", "B", 15),
+    ...         ("D", "C", 2),
+    ...     }
+    ... )
+    >>> cycle = approx.threshold_accepting_tsp(G, "greedy", source="D")
+    >>> cost = sum(G[n][nbr]["weight"] for n, nbr in nx.utils.pairwise(cycle))
+    >>> cycle
+    ['D', 'C', 'B', 'A', 'D']
+    >>> cost
+    31
+    >>> incycle = ["D", "B", "A", "C", "D"]
+    >>> cycle = approx.threshold_accepting_tsp(G, incycle, source="D")
+    >>> cost = sum(G[n][nbr]["weight"] for n, nbr in nx.utils.pairwise(cycle))
+    >>> cycle
+    ['D', 'C', 'B', 'A', 'D']
+    >>> cost
+    31
+
+    Notes
+    -----
+    Threshold Accepting is a metaheuristic local search algorithm.
+    The main characteristic of this algorithm is that it accepts
+    even solutions which lead to the increase of the cost in order
+    to escape from low quality local optimal solutions.
+
+    This algorithm needs an initial solution. This solution can be
+    constructed by a simple greedy algorithm. At every iteration, it
+    selects thoughtfully a neighbor solution.
+    Consider $c(x)$ cost of current solution and $c(x')$ cost of
+    neighbor solution.
+    If $c(x') - c(x) <= threshold$ then the neighbor solution becomes the current
+    solution for the next iteration, where the threshold is named threshold.
+
+    In comparison to the Simulated Annealing algorithm, the Threshold
+    Accepting algorithm does not accept very low quality solutions
+    (due to the presence of the threshold value). In the case of
+    Simulated Annealing, even a very low quality solution can
+    be accepted with probability $p$.
+
+    Time complexity:
+    It has a running time $O(m * n * |V|)$ where $m$ and $n$ are the number
+    of times the outer and inner loop run respectively.
+
+    For more information and how algorithm is inspired see:
+    https://doi.org/10.1016/0021-9991(90)90201-B
+
+    See Also
+    --------
+    simulated_annealing_tsp
+
+    """
+    if move == "1-1":
+        move = swap_two_nodes
+    elif move == "1-0":
+        move = move_one_node
+    if init_cycle == "greedy":
+        # Construct an initial solution using a greedy algorithm.
+        cycle = greedy_tsp(G, weight=weight, source=source)
+        if G.number_of_nodes() == 2:
+            return cycle
+
+    else:
+        cycle = list(init_cycle)
+        if source is None:
+            source = cycle[0]
+        elif source != cycle[0]:
+            raise nx.NetworkXError("source must be first node in init_cycle")
+        if cycle[0] != cycle[-1]:
+            raise nx.NetworkXError("init_cycle must be a cycle. (return to start)")
+
+        if len(cycle) - 1 != len(G) or len(set(G.nbunch_iter(cycle))) != len(G):
+            raise nx.NetworkXError("init_cycle is not all and only nodes.")
+
+        # Check that G is a complete graph
+        N = len(G) - 1
+        # This check ignores selfloops which is what we want here.
+        if any(len(nbrdict) - (n in nbrdict) != N for n, nbrdict in G.adj.items()):
+            raise nx.NetworkXError("G must be a complete graph.")
+
+        if G.number_of_nodes() == 2:
+            neighbor = list(G.neighbors(source))[0]
+            return [source, neighbor, source]
+
+    # Find the cost of initial solution
+    cost = sum(G[u][v].get(weight, 1) for u, v in pairwise(cycle))
+
+    count = 0
+    best_cycle = cycle.copy()
+    best_cost = cost
+    while count <= max_iterations:
+        count += 1
+        accepted = False
+        for i in range(N_inner):
+            adj_sol = move(cycle, seed)
+            adj_cost = sum(G[u][v].get(weight, 1) for u, v in pairwise(adj_sol))
+            delta = adj_cost - cost
+            if delta <= threshold:
+                accepted = True
+
+                # Set current solution the adjacent solution.
+                cycle = adj_sol
+                cost = adj_cost
+
+                if cost < best_cost:
+                    count = 0
+                    best_cycle = cycle.copy()
+                    best_cost = cost
+        if accepted:
+            threshold -= threshold * alpha
+
+    return best_cycle

venv/lib/python3.10/site-packages/networkx/algorithms/approximation/treewidth.py

@@ -0,0 +1,252 @@
+"""Functions for computing treewidth decomposition.
+
+Treewidth of an undirected graph is a number associated with the graph.
+It can be defined as the size of the largest vertex set (bag) in a tree
+decomposition of the graph minus one.
+
+`Wikipedia: Treewidth <https://en.wikipedia.org/wiki/Treewidth>`_
+
+The notions of treewidth and tree decomposition have gained their
+attractiveness partly because many graph and network problems that are
+intractable (e.g., NP-hard) on arbitrary graphs become efficiently
+solvable (e.g., with a linear time algorithm) when the treewidth of the
+input graphs is bounded by a constant [1]_ [2]_.
+
+There are two different functions for computing a tree decomposition:
+:func:`treewidth_min_degree` and :func:`treewidth_min_fill_in`.
+
+.. [1] Hans L. Bodlaender and Arie M. C. A. Koster. 2010. "Treewidth
+      computations I.Upper bounds". Inf. Comput. 208, 3 (March 2010),259-275.
+      http://dx.doi.org/10.1016/j.ic.2009.03.008
+
+.. [2] Hans L. Bodlaender. "Discovering Treewidth". Institute of Information
+      and Computing Sciences, Utrecht University.
+      Technical Report UU-CS-2005-018.
+      http://www.cs.uu.nl
+
+.. [3] K. Wang, Z. Lu, and J. Hicks *Treewidth*.
+      https://web.archive.org/web/20210507025929/http://web.eecs.utk.edu/~cphill25/cs594_spring2015_projects/treewidth.pdf
+
+"""
+
+import itertools
+import sys
+from heapq import heapify, heappop, heappush
+
+import networkx as nx
+from networkx.utils import not_implemented_for
+
+__all__ = ["treewidth_min_degree", "treewidth_min_fill_in"]
+
+
+@not_implemented_for("directed")
+@not_implemented_for("multigraph")
+@nx._dispatchable(returns_graph=True)
+def treewidth_min_degree(G):
+    """Returns a treewidth decomposition using the Minimum Degree heuristic.
+
+    The heuristic chooses the nodes according to their degree, i.e., first
+    the node with the lowest degree is chosen, then the graph is updated
+    and the corresponding node is removed. Next, a new node with the lowest
+    degree is chosen, and so on.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+
+    Returns
+    -------
+    Treewidth decomposition : (int, Graph) tuple
+          2-tuple with treewidth and the corresponding decomposed tree.
+    """
+    deg_heuristic = MinDegreeHeuristic(G)
+    return treewidth_decomp(G, lambda graph: deg_heuristic.best_node(graph))
+
+
+@not_implemented_for("directed")
+@not_implemented_for("multigraph")
+@nx._dispatchable(returns_graph=True)
+def treewidth_min_fill_in(G):
+    """Returns a treewidth decomposition using the Minimum Fill-in heuristic.
+
+    The heuristic chooses a node from the graph, where the number of edges
+    added turning the neighborhood of the chosen node into clique is as
+    small as possible.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+
+    Returns
+    -------
+    Treewidth decomposition : (int, Graph) tuple
+        2-tuple with treewidth and the corresponding decomposed tree.
+    """
+    return treewidth_decomp(G, min_fill_in_heuristic)
+
+
+class MinDegreeHeuristic:
+    """Implements the Minimum Degree heuristic.
+
+    The heuristic chooses the nodes according to their degree
+    (number of neighbors), i.e., first the node with the lowest degree is
+    chosen, then the graph is updated and the corresponding node is
+    removed. Next, a new node with the lowest degree is chosen, and so on.
+    """
+
+    def __init__(self, graph):
+        self._graph = graph
+
+        # nodes that have to be updated in the heap before each iteration
+        self._update_nodes = []
+
+        self._degreeq = []  # a heapq with 3-tuples (degree,unique_id,node)
+        self.count = itertools.count()
+
+        # build heap with initial degrees
+        for n in graph:
+            self._degreeq.append((len(graph[n]), next(self.count), n))
+        heapify(self._degreeq)
+
+    def best_node(self, graph):
+        # update nodes in self._update_nodes
+        for n in self._update_nodes:
+            # insert changed degrees into degreeq
+            heappush(self._degreeq, (len(graph[n]), next(self.count), n))
+
+        # get the next valid (minimum degree) node
+        while self._degreeq:
+            (min_degree, _, elim_node) = heappop(self._degreeq)
+            if elim_node not in graph or len(graph[elim_node]) != min_degree:
+                # outdated entry in degreeq
+                continue
+            elif min_degree == len(graph) - 1:
+                # fully connected: abort condition
+                return None
+
+            # remember to update nodes in the heap before getting the next node
+            self._update_nodes = graph[elim_node]
+            return elim_node
+
+        # the heap is empty: abort
+        return None
+
+
+def min_fill_in_heuristic(graph):
+    """Implements the Minimum Degree heuristic.
+
+    Returns the node from the graph, where the number of edges added when
+    turning the neighborhood of the chosen node into clique is as small as
+    possible. This algorithm chooses the nodes using the Minimum Fill-In
+    heuristic. The running time of the algorithm is :math:`O(V^3)` and it uses
+    additional constant memory."""
+
+    if len(graph) == 0:
+        return None
+
+    min_fill_in_node = None
+
+    min_fill_in = sys.maxsize
+
+    # sort nodes by degree
+    nodes_by_degree = sorted(graph, key=lambda x: len(graph[x]))
+    min_degree = len(graph[nodes_by_degree[0]])
+
+    # abort condition (handle complete graph)
+    if min_degree == len(graph) - 1:
+        return None
+
+    for node in nodes_by_degree:
+        num_fill_in = 0
+        nbrs = graph[node]
+        for nbr in nbrs:
+            # count how many nodes in nbrs current nbr is not connected to
+            # subtract 1 for the node itself
+            num_fill_in += len(nbrs - graph[nbr]) - 1
+            if num_fill_in >= 2 * min_fill_in:
+                break
+
+        num_fill_in /= 2  # divide by 2 because of double counting
+
+        if num_fill_in < min_fill_in:  # update min-fill-in node
+            if num_fill_in == 0:
+                return node
+            min_fill_in = num_fill_in
+            min_fill_in_node = node
+
+    return min_fill_in_node
+
+
+@nx._dispatchable(returns_graph=True)
+def treewidth_decomp(G, heuristic=min_fill_in_heuristic):
+    """Returns a treewidth decomposition using the passed heuristic.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+    heuristic : heuristic function
+
+    Returns
+    -------
+    Treewidth decomposition : (int, Graph) tuple
+        2-tuple with treewidth and the corresponding decomposed tree.
+    """
+
+    # make dict-of-sets structure
+    graph = {n: set(G[n]) - {n} for n in G}
+
+    # stack containing nodes and neighbors in the order from the heuristic
+    node_stack = []
+
+    # get first node from heuristic
+    elim_node = heuristic(graph)
+    while elim_node is not None:
+        # connect all neighbors with each other
+        nbrs = graph[elim_node]
+        for u, v in itertools.permutations(nbrs, 2):
+            if v not in graph[u]:
+                graph[u].add(v)
+
+        # push node and its current neighbors on stack
+        node_stack.append((elim_node, nbrs))
+
+        # remove node from graph
+        for u in graph[elim_node]:
+            graph[u].remove(elim_node)
+
+        del graph[elim_node]
+        elim_node = heuristic(graph)
+
+    # the abort condition is met; put all remaining nodes into one bag
+    decomp = nx.Graph()
+    first_bag = frozenset(graph.keys())
+    decomp.add_node(first_bag)
+
+    treewidth = len(first_bag) - 1
+
+    while node_stack:
+        # get node and its neighbors from the stack
+        (curr_node, nbrs) = node_stack.pop()
+
+        # find a bag all neighbors are in
+        old_bag = None
+        for bag in decomp.nodes:
+            if nbrs <= bag:
+                old_bag = bag
+                break
+
+        if old_bag is None:
+            # no old_bag was found: just connect to the first_bag
+            old_bag = first_bag
+
+        # create new node for decomposition
+        nbrs.add(curr_node)
+        new_bag = frozenset(nbrs)
+
+        # update treewidth
+        treewidth = max(treewidth, len(new_bag) - 1)
+
+        # add edge to decomposition (implicitly also adds the new node)
+        decomp.add_edge(old_bag, new_bag)
+
+    return treewidth, decomp

venv/lib/python3.10/site-packages/networkx/algorithms/approximation/vertex_cover.py

@@ -0,0 +1,82 @@
+"""Functions for computing an approximate minimum weight vertex cover.
+
+A |vertex cover|_ is a subset of nodes such that each edge in the graph
+is incident to at least one node in the subset.
+
+.. _vertex cover: https://en.wikipedia.org/wiki/Vertex_cover
+.. |vertex cover| replace:: *vertex cover*
+
+"""
+import networkx as nx
+
+__all__ = ["min_weighted_vertex_cover"]
+
+
+@nx._dispatchable(node_attrs="weight")
+def min_weighted_vertex_cover(G, weight=None):
+    r"""Returns an approximate minimum weighted vertex cover.
+
+    The set of nodes returned by this function is guaranteed to be a
+    vertex cover, and the total weight of the set is guaranteed to be at
+    most twice the total weight of the minimum weight vertex cover. In
+    other words,
+
+    .. math::
+
+       w(S) \leq 2 * w(S^*),
+
+    where $S$ is the vertex cover returned by this function,
+    $S^*$ is the vertex cover of minimum weight out of all vertex
+    covers of the graph, and $w$ is the function that computes the
+    sum of the weights of each node in that given set.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+
+    weight : string, optional (default = None)
+        If None, every node has weight 1. If a string, use this node
+        attribute as the node weight. A node without this attribute is
+        assumed to have weight 1.
+
+    Returns
+    -------
+    min_weighted_cover : set
+        Returns a set of nodes whose weight sum is no more than twice
+        the weight sum of the minimum weight vertex cover.
+
+    Notes
+    -----
+    For a directed graph, a vertex cover has the same definition: a set
+    of nodes such that each edge in the graph is incident to at least
+    one node in the set. Whether the node is the head or tail of the
+    directed edge is ignored.
+
+    This is the local-ratio algorithm for computing an approximate
+    vertex cover. The algorithm greedily reduces the costs over edges,
+    iteratively building a cover. The worst-case runtime of this
+    implementation is $O(m \log n)$, where $n$ is the number
+    of nodes and $m$ the number of edges in the graph.
+
+    References
+    ----------
+    .. [1] Bar-Yehuda, R., and Even, S. (1985). "A local-ratio theorem for
+       approximating the weighted vertex cover problem."
+       *Annals of Discrete Mathematics*, 25, 27–46
+       <http://www.cs.technion.ac.il/~reuven/PDF/vc_lr.pdf>
+
+    """
+    cost = dict(G.nodes(data=weight, default=1))
+    # While there are uncovered edges, choose an uncovered and update
+    # the cost of the remaining edges.
+    cover = set()
+    for u, v in G.edges():
+        if u in cover or v in cover:
+            continue
+        if cost[u] <= cost[v]:
+            cover.add(u)
+            cost[v] -= cost[u]
+        else:
+            cover.add(v)
+            cost[u] -= cost[v]
+    return cover

venv/lib/python3.10/site-packages/networkx/algorithms/boundary.py

@@ -0,0 +1,167 @@
+"""Routines to find the boundary of a set of nodes.
+
+An edge boundary is a set of edges, each of which has exactly one
+endpoint in a given set of nodes (or, in the case of directed graphs,
+the set of edges whose source node is in the set).
+
+A node boundary of a set *S* of nodes is the set of (out-)neighbors of
+nodes in *S* that are outside *S*.
+
+"""
+from itertools import chain
+
+import networkx as nx
+
+__all__ = ["edge_boundary", "node_boundary"]
+
+
+@nx._dispatchable(edge_attrs={"data": "default"}, preserve_edge_attrs="data")
+def edge_boundary(G, nbunch1, nbunch2=None, data=False, keys=False, default=None):
+    """Returns the edge boundary of `nbunch1`.
+
+    The *edge boundary* of a set *S* with respect to a set *T* is the
+    set of edges (*u*, *v*) such that *u* is in *S* and *v* is in *T*.
+    If *T* is not specified, it is assumed to be the set of all nodes
+    not in *S*.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+
+    nbunch1 : iterable
+        Iterable of nodes in the graph representing the set of nodes
+        whose edge boundary will be returned. (This is the set *S* from
+        the definition above.)
+
+    nbunch2 : iterable
+        Iterable of nodes representing the target (or "exterior") set of
+        nodes. (This is the set *T* from the definition above.) If not
+        specified, this is assumed to be the set of all nodes in `G`
+        not in `nbunch1`.
+
+    keys : bool
+        This parameter has the same meaning as in
+        :meth:`MultiGraph.edges`.
+
+    data : bool or object
+        This parameter has the same meaning as in
+        :meth:`MultiGraph.edges`.
+
+    default : object
+        This parameter has the same meaning as in
+        :meth:`MultiGraph.edges`.
+
+    Returns
+    -------
+    iterator
+        An iterator over the edges in the boundary of `nbunch1` with
+        respect to `nbunch2`. If `keys`, `data`, or `default`
+        are specified and `G` is a multigraph, then edges are returned
+        with keys and/or data, as in :meth:`MultiGraph.edges`.
+
+    Examples
+    --------
+    >>> G = nx.wheel_graph(6)
+
+    When nbunch2=None:
+
+    >>> list(nx.edge_boundary(G, (1, 3)))
+    [(1, 0), (1, 2), (1, 5), (3, 0), (3, 2), (3, 4)]
+
+    When nbunch2 is given:
+
+    >>> list(nx.edge_boundary(G, (1, 3), (2, 0)))
+    [(1, 0), (1, 2), (3, 0), (3, 2)]
+
+    Notes
+    -----
+    Any element of `nbunch` that is not in the graph `G` will be
+    ignored.
+
+    `nbunch1` and `nbunch2` are usually meant to be disjoint, but in
+    the interest of speed and generality, that is not required here.
+
+    """
+    nset1 = {n for n in nbunch1 if n in G}
+    # Here we create an iterator over edges incident to nodes in the set
+    # `nset1`. The `Graph.edges()` method does not provide a guarantee
+    # on the orientation of the edges, so our algorithm below must
+    # handle the case in which exactly one orientation, either (u, v) or
+    # (v, u), appears in this iterable.
+    if G.is_multigraph():
+        edges = G.edges(nset1, data=data, keys=keys, default=default)
+    else:
+        edges = G.edges(nset1, data=data, default=default)
+    # If `nbunch2` is not provided, then it is assumed to be the set
+    # complement of `nbunch1`. For the sake of efficiency, this is
+    # implemented by using the `not in` operator, instead of by creating
+    # an additional set and using the `in` operator.
+    if nbunch2 is None:
+        return (e for e in edges if (e[0] in nset1) ^ (e[1] in nset1))
+    nset2 = set(nbunch2)
+    return (
+        e
+        for e in edges
+        if (e[0] in nset1 and e[1] in nset2) or (e[1] in nset1 and e[0] in nset2)
+    )
+
+
+@nx._dispatchable
+def node_boundary(G, nbunch1, nbunch2=None):
+    """Returns the node boundary of `nbunch1`.
+
+    The *node boundary* of a set *S* with respect to a set *T* is the
+    set of nodes *v* in *T* such that for some *u* in *S*, there is an
+    edge joining *u* to *v*. If *T* is not specified, it is assumed to
+    be the set of all nodes not in *S*.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+
+    nbunch1 : iterable
+        Iterable of nodes in the graph representing the set of nodes
+        whose node boundary will be returned. (This is the set *S* from
+        the definition above.)
+
+    nbunch2 : iterable
+        Iterable of nodes representing the target (or "exterior") set of
+        nodes. (This is the set *T* from the definition above.) If not
+        specified, this is assumed to be the set of all nodes in `G`
+        not in `nbunch1`.
+
+    Returns
+    -------
+    set
+        The node boundary of `nbunch1` with respect to `nbunch2`.
+
+    Examples
+    --------
+    >>> G = nx.wheel_graph(6)
+
+    When nbunch2=None:
+
+    >>> list(nx.node_boundary(G, (3, 4)))
+    [0, 2, 5]
+
+    When nbunch2 is given:
+
+    >>> list(nx.node_boundary(G, (3, 4), (0, 1, 5)))
+    [0, 5]
+
+    Notes
+    -----
+    Any element of `nbunch` that is not in the graph `G` will be
+    ignored.
+
+    `nbunch1` and `nbunch2` are usually meant to be disjoint, but in
+    the interest of speed and generality, that is not required here.
+
+    """
+    nset1 = {n for n in nbunch1 if n in G}
+    bdy = set(chain.from_iterable(G[v] for v in nset1)) - nset1
+    # If `nbunch2` is not specified, it is assumed to be the set
+    # complement of `nbunch1`.
+    if nbunch2 is not None:
+        bdy &= set(nbunch2)
+    return bdy

venv/lib/python3.10/site-packages/networkx/algorithms/bridges.py

@@ -0,0 +1,205 @@
+"""Bridge-finding algorithms."""
+from itertools import chain
+
+import networkx as nx
+from networkx.utils import not_implemented_for
+
+__all__ = ["bridges", "has_bridges", "local_bridges"]
+
+
+@not_implemented_for("directed")
+@nx._dispatchable
+def bridges(G, root=None):
+    """Generate all bridges in a graph.
+
+    A *bridge* in a graph is an edge whose removal causes the number of
+    connected components of the graph to increase.  Equivalently, a bridge is an
+    edge that does not belong to any cycle. Bridges are also known as cut-edges,
+    isthmuses, or cut arcs.
+
+    Parameters
+    ----------
+    G : undirected graph
+
+    root : node (optional)
+       A node in the graph `G`. If specified, only the bridges in the
+       connected component containing this node will be returned.
+
+    Yields
+    ------
+    e : edge
+       An edge in the graph whose removal disconnects the graph (or
+       causes the number of connected components to increase).
+
+    Raises
+    ------
+    NodeNotFound
+       If `root` is not in the graph `G`.
+
+    NetworkXNotImplemented
+        If `G` is a directed graph.
+
+    Examples
+    --------
+    The barbell graph with parameter zero has a single bridge:
+
+    >>> G = nx.barbell_graph(10, 0)
+    >>> list(nx.bridges(G))
+    [(9, 10)]
+
+    Notes
+    -----
+    This is an implementation of the algorithm described in [1]_.  An edge is a
+    bridge if and only if it is not contained in any chain. Chains are found
+    using the :func:`networkx.chain_decomposition` function.
+
+    The algorithm described in [1]_ requires a simple graph. If the provided
+    graph is a multigraph, we convert it to a simple graph and verify that any
+    bridges discovered by the chain decomposition algorithm are not multi-edges.
+
+    Ignoring polylogarithmic factors, the worst-case time complexity is the
+    same as the :func:`networkx.chain_decomposition` function,
+    $O(m + n)$, where $n$ is the number of nodes in the graph and $m$ is
+    the number of edges.
+
+    References
+    ----------
+    .. [1] https://en.wikipedia.org/wiki/Bridge_%28graph_theory%29#Bridge-Finding_with_Chain_Decompositions
+    """
+    multigraph = G.is_multigraph()
+    H = nx.Graph(G) if multigraph else G
+    chains = nx.chain_decomposition(H, root=root)
+    chain_edges = set(chain.from_iterable(chains))
+    H_copy = H.copy()
+    if root is not None:
+        H = H.subgraph(nx.node_connected_component(H, root)).copy()
+    for u, v in H.edges():
+        if (u, v) not in chain_edges and (v, u) not in chain_edges:
+            if multigraph and len(G[u][v]) > 1:
+                continue
+            yield u, v
+
+
+@not_implemented_for("directed")
+@nx._dispatchable
+def has_bridges(G, root=None):
+    """Decide whether a graph has any bridges.
+
+    A *bridge* in a graph is an edge whose removal causes the number of
+    connected components of the graph to increase.
+
+    Parameters
+    ----------
+    G : undirected graph
+
+    root : node (optional)
+       A node in the graph `G`. If specified, only the bridges in the
+       connected component containing this node will be considered.
+
+    Returns
+    -------
+    bool
+       Whether the graph (or the connected component containing `root`)
+       has any bridges.
+
+    Raises
+    ------
+    NodeNotFound
+       If `root` is not in the graph `G`.
+
+    NetworkXNotImplemented
+        If `G` is a directed graph.
+
+    Examples
+    --------
+    The barbell graph with parameter zero has a single bridge::
+
+        >>> G = nx.barbell_graph(10, 0)
+        >>> nx.has_bridges(G)
+        True
+
+    On the other hand, the cycle graph has no bridges::
+
+        >>> G = nx.cycle_graph(5)
+        >>> nx.has_bridges(G)
+        False
+
+    Notes
+    -----
+    This implementation uses the :func:`networkx.bridges` function, so
+    it shares its worst-case time complexity, $O(m + n)$, ignoring
+    polylogarithmic factors, where $n$ is the number of nodes in the
+    graph and $m$ is the number of edges.
+
+    """
+    try:
+        next(bridges(G, root=root))
+    except StopIteration:
+        return False
+    else:
+        return True
+
+
+@not_implemented_for("multigraph")
+@not_implemented_for("directed")
+@nx._dispatchable(edge_attrs="weight")
+def local_bridges(G, with_span=True, weight=None):
+    """Iterate over local bridges of `G` optionally computing the span
+
+    A *local bridge* is an edge whose endpoints have no common neighbors.
+    That is, the edge is not part of a triangle in the graph.
+
+    The *span* of a *local bridge* is the shortest path length between
+    the endpoints if the local bridge is removed.
+
+    Parameters
+    ----------
+    G : undirected graph
+
+    with_span : bool
+        If True, yield a 3-tuple `(u, v, span)`
+
+    weight : function, string or None (default: None)
+        If function, used to compute edge weights for the span.
+        If string, the edge data attribute used in calculating span.
+        If None, all edges have weight 1.
+
+    Yields
+    ------
+    e : edge
+        The local bridges as an edge 2-tuple of nodes `(u, v)` or
+        as a 3-tuple `(u, v, span)` when `with_span is True`.
+
+    Raises
+    ------
+    NetworkXNotImplemented
+        If `G` is a directed graph or multigraph.
+
+    Examples
+    --------
+    A cycle graph has every edge a local bridge with span N-1.
+
+       >>> G = nx.cycle_graph(9)
+       >>> (0, 8, 8) in set(nx.local_bridges(G))
+       True
+    """
+    if with_span is not True:
+        for u, v in G.edges:
+            if not (set(G[u]) & set(G[v])):
+                yield u, v
+    else:
+        wt = nx.weighted._weight_function(G, weight)
+        for u, v in G.edges:
+            if not (set(G[u]) & set(G[v])):
+                enodes = {u, v}
+
+                def hide_edge(n, nbr, d):
+                    if n not in enodes or nbr not in enodes:
+                        return wt(n, nbr, d)
+                    return None
+
+                try:
+                    span = nx.shortest_path_length(G, u, v, weight=hide_edge)
+                    yield u, v, span
+                except nx.NetworkXNoPath:
+                    yield u, v, float("inf")

venv/lib/python3.10/site-packages/networkx/algorithms/broadcasting.py

@@ -0,0 +1,155 @@
+"""Routines to calculate the broadcast time of certain graphs.
+
+Broadcasting is an information dissemination problem in which a node in a graph,
+called the originator, must distribute a message to all other nodes by placing
+a series of calls along the edges of the graph. Once informed, other nodes aid
+the originator in distributing the message.
+
+The broadcasting must be completed as quickly as possible subject to the
+following constraints:
+- Each call requires one unit of time.
+- A node can only participate in one call per unit of time.
+- Each call only involves two adjacent nodes: a sender and a receiver.
+"""
+
+import networkx as nx
+from networkx import NetworkXError
+from networkx.utils import not_implemented_for
+
+__all__ = [
+    "tree_broadcast_center",
+    "tree_broadcast_time",
+]
+
+
+def _get_max_broadcast_value(G, U, v, values):
+    adj = sorted(set(G.neighbors(v)) & U, key=values.get, reverse=True)
+    return max(values[u] + i for i, u in enumerate(adj, start=1))
+
+
+def _get_broadcast_centers(G, v, values, target):
+    adj = sorted(G.neighbors(v), key=values.get, reverse=True)
+    j = next(i for i, u in enumerate(adj, start=1) if values[u] + i == target)
+    return set([v] + adj[:j])
+
+
+@not_implemented_for("directed")
+@not_implemented_for("multigraph")
+@nx._dispatchable
+def tree_broadcast_center(G):
+    """Return the Broadcast Center of the tree `G`.
+
+    The broadcast center of a graph G denotes the set of nodes having
+    minimum broadcast time [1]_. This is a linear algorithm for determining
+    the broadcast center of a tree with ``N`` nodes, as a by-product it also
+    determines the broadcast time from the broadcast center.
+
+    Parameters
+    ----------
+    G : undirected graph
+        The graph should be an undirected tree
+
+    Returns
+    -------
+    BC : (int, set) tuple
+        minimum broadcast number of the tree, set of broadcast centers
+
+    Raises
+    ------
+    NetworkXNotImplemented
+        If the graph is directed or is a multigraph.
+
+    References
+    ----------
+    .. [1] Slater, P.J., Cockayne, E.J., Hedetniemi, S.T,
+       Information dissemination in trees. SIAM J.Comput. 10(4), 692–701 (1981)
+    """
+    # Assert that the graph G is a tree
+    if not nx.is_tree(G):
+        NetworkXError("Input graph is not a tree")
+    # step 0
+    if G.number_of_nodes() == 2:
+        return 1, set(G.nodes())
+    if G.number_of_nodes() == 1:
+        return 0, set(G.nodes())
+
+    # step 1
+    U = {node for node, deg in G.degree if deg == 1}
+    values = {n: 0 for n in U}
+    T = G.copy()
+    T.remove_nodes_from(U)
+
+    # step 2
+    W = {node for node, deg in T.degree if deg == 1}
+    values.update((w, G.degree[w] - 1) for w in W)
+
+    # step 3
+    while T.number_of_nodes() >= 2:
+        # step 4
+        w = min(W, key=lambda n: values[n])
+        v = next(T.neighbors(w))
+
+        # step 5
+        U.add(w)
+        W.remove(w)
+        T.remove_node(w)
+
+        # step 6
+        if T.degree(v) == 1:
+            # update t(v)
+            values.update({v: _get_max_broadcast_value(G, U, v, values)})
+            W.add(v)
+
+    # step 7
+    v = nx.utils.arbitrary_element(T)
+    b_T = _get_max_broadcast_value(G, U, v, values)
+    return b_T, _get_broadcast_centers(G, v, values, b_T)
+
+
+@not_implemented_for("directed")
+@not_implemented_for("multigraph")
+@nx._dispatchable
+def tree_broadcast_time(G, node=None):
+    """Return the Broadcast Time of the tree `G`.
+
+    The minimum broadcast time of a node is defined as the minimum amount
+    of time required to complete broadcasting starting from the
+    originator. The broadcast time of a graph is the maximum over
+    all nodes of the minimum broadcast time from that node [1]_.
+    This function returns the minimum broadcast time of `node`.
+    If `node` is None the broadcast time for the graph is returned.
+
+    Parameters
+    ----------
+    G : undirected graph
+        The graph should be an undirected tree
+    node: int, optional
+        index of starting node. If `None`, the algorithm returns the broadcast
+        time of the tree.
+
+    Returns
+    -------
+    BT : int
+        Broadcast Time of a node in a tree
+
+    Raises
+    ------
+    NetworkXNotImplemented
+        If the graph is directed or is a multigraph.
+
+    References
+    ----------
+    .. [1] Harutyunyan, H. A. and Li, Z.
+        "A Simple Construction of Broadcast Graphs."
+        In Computing and Combinatorics. COCOON 2019
+        (Ed. D. Z. Du and C. Tian.) Springer, pp. 240-253, 2019.
+    """
+    b_T, b_C = tree_broadcast_center(G)
+    if node is not None:
+        return b_T + min(nx.shortest_path_length(G, node, u) for u in b_C)
+    dist_from_center = dict.fromkeys(G, len(G))
+    for u in b_C:
+        for v, dist in nx.shortest_path_length(G, u).items():
+            if dist < dist_from_center[v]:
+                dist_from_center[v] = dist
+    return b_T + max(dist_from_center.values())

venv/lib/python3.10/site-packages/networkx/algorithms/chordal.py

@@ -0,0 +1,442 @@
+"""
+Algorithms for chordal graphs.
+
+A graph is chordal if every cycle of length at least 4 has a chord
+(an edge joining two nodes not adjacent in the cycle).
+https://en.wikipedia.org/wiki/Chordal_graph
+"""
+import sys
+
+import networkx as nx
+from networkx.algorithms.components import connected_components
+from networkx.utils import arbitrary_element, not_implemented_for
+
+__all__ = [
+    "is_chordal",
+    "find_induced_nodes",
+    "chordal_graph_cliques",
+    "chordal_graph_treewidth",
+    "NetworkXTreewidthBoundExceeded",
+    "complete_to_chordal_graph",
+]
+
+
+class NetworkXTreewidthBoundExceeded(nx.NetworkXException):
+    """Exception raised when a treewidth bound has been provided and it has
+    been exceeded"""
+
+
+@not_implemented_for("directed")
+@not_implemented_for("multigraph")
+@nx._dispatchable
+def is_chordal(G):
+    """Checks whether G is a chordal graph.
+
+    A graph is chordal if every cycle of length at least 4 has a chord
+    (an edge joining two nodes not adjacent in the cycle).
+
+    Parameters
+    ----------
+    G : graph
+      A NetworkX graph.
+
+    Returns
+    -------
+    chordal : bool
+      True if G is a chordal graph and False otherwise.
+
+    Raises
+    ------
+    NetworkXNotImplemented
+        The algorithm does not support DiGraph, MultiGraph and MultiDiGraph.
+
+    Examples
+    --------
+    >>> e = [
+    ...     (1, 2),
+    ...     (1, 3),
+    ...     (2, 3),
+    ...     (2, 4),
+    ...     (3, 4),
+    ...     (3, 5),
+    ...     (3, 6),
+    ...     (4, 5),
+    ...     (4, 6),
+    ...     (5, 6),
+    ... ]
+    >>> G = nx.Graph(e)
+    >>> nx.is_chordal(G)
+    True
+
+    Notes
+    -----
+    The routine tries to go through every node following maximum cardinality
+    search. It returns False when it finds that the separator for any node
+    is not a clique.  Based on the algorithms in [1]_.
+
+    Self loops are ignored.
+
+    References
+    ----------
+    .. [1] R. E. Tarjan and M. Yannakakis, Simple linear-time algorithms
+       to test chordality of graphs, test acyclicity of hypergraphs, and
+       selectively reduce acyclic hypergraphs, SIAM J. Comput., 13 (1984),
+       pp. 566–579.
+    """
+    if len(G.nodes) <= 3:
+        return True
+    return len(_find_chordality_breaker(G)) == 0
+
+
+@nx._dispatchable
+def find_induced_nodes(G, s, t, treewidth_bound=sys.maxsize):
+    """Returns the set of induced nodes in the path from s to t.
+
+    Parameters
+    ----------
+    G : graph
+      A chordal NetworkX graph
+    s : node
+        Source node to look for induced nodes
+    t : node
+        Destination node to look for induced nodes
+    treewidth_bound: float
+        Maximum treewidth acceptable for the graph H. The search
+        for induced nodes will end as soon as the treewidth_bound is exceeded.
+
+    Returns
+    -------
+    induced_nodes : Set of nodes
+        The set of induced nodes in the path from s to t in G
+
+    Raises
+    ------
+    NetworkXError
+        The algorithm does not support DiGraph, MultiGraph and MultiDiGraph.
+        If the input graph is an instance of one of these classes, a
+        :exc:`NetworkXError` is raised.
+        The algorithm can only be applied to chordal graphs. If the input
+        graph is found to be non-chordal, a :exc:`NetworkXError` is raised.
+
+    Examples
+    --------
+    >>> G = nx.Graph()
+    >>> G = nx.generators.classic.path_graph(10)
+    >>> induced_nodes = nx.find_induced_nodes(G, 1, 9, 2)
+    >>> sorted(induced_nodes)
+    [1, 2, 3, 4, 5, 6, 7, 8, 9]
+
+    Notes
+    -----
+    G must be a chordal graph and (s,t) an edge that is not in G.
+
+    If a treewidth_bound is provided, the search for induced nodes will end
+    as soon as the treewidth_bound is exceeded.
+
+    The algorithm is inspired by Algorithm 4 in [1]_.
+    A formal definition of induced node can also be found on that reference.
+
+    Self Loops are ignored
+
+    References
+    ----------
+    .. [1] Learning Bounded Treewidth Bayesian Networks.
+       Gal Elidan, Stephen Gould; JMLR, 9(Dec):2699--2731, 2008.
+       http://jmlr.csail.mit.edu/papers/volume9/elidan08a/elidan08a.pdf
+    """
+    if not is_chordal(G):
+        raise nx.NetworkXError("Input graph is not chordal.")
+
+    H = nx.Graph(G)
+    H.add_edge(s, t)
+    induced_nodes = set()
+    triplet = _find_chordality_breaker(H, s, treewidth_bound)
+    while triplet:
+        (u, v, w) = triplet
+        induced_nodes.update(triplet)
+        for n in triplet:
+            if n != s:
+                H.add_edge(s, n)
+        triplet = _find_chordality_breaker(H, s, treewidth_bound)
+    if induced_nodes:
+        # Add t and the second node in the induced path from s to t.
+        induced_nodes.add(t)
+        for u in G[s]:
+            if len(induced_nodes & set(G[u])) == 2:
+                induced_nodes.add(u)
+                break
+    return induced_nodes
+
+
+@nx._dispatchable
+def chordal_graph_cliques(G):
+    """Returns all maximal cliques of a chordal graph.
+
+    The algorithm breaks the graph in connected components and performs a
+    maximum cardinality search in each component to get the cliques.
+
+    Parameters
+    ----------
+    G : graph
+      A NetworkX graph
+
+    Yields
+    ------
+    frozenset of nodes
+        Maximal cliques, each of which is a frozenset of
+        nodes in `G`. The order of cliques is arbitrary.
+
+    Raises
+    ------
+    NetworkXError
+        The algorithm does not support DiGraph, MultiGraph and MultiDiGraph.
+        The algorithm can only be applied to chordal graphs. If the input
+        graph is found to be non-chordal, a :exc:`NetworkXError` is raised.
+
+    Examples
+    --------
+    >>> e = [
+    ...     (1, 2),
+    ...     (1, 3),
+    ...     (2, 3),
+    ...     (2, 4),
+    ...     (3, 4),
+    ...     (3, 5),
+    ...     (3, 6),
+    ...     (4, 5),
+    ...     (4, 6),
+    ...     (5, 6),
+    ...     (7, 8),
+    ... ]
+    >>> G = nx.Graph(e)
+    >>> G.add_node(9)
+    >>> cliques = [c for c in chordal_graph_cliques(G)]
+    >>> cliques[0]
+    frozenset({1, 2, 3})
+    """
+    for C in (G.subgraph(c).copy() for c in connected_components(G)):
+        if C.number_of_nodes() == 1:
+            if nx.number_of_selfloops(C) > 0:
+                raise nx.NetworkXError("Input graph is not chordal.")
+            yield frozenset(C.nodes())
+        else:
+            unnumbered = set(C.nodes())
+            v = arbitrary_element(C)
+            unnumbered.remove(v)
+            numbered = {v}
+            clique_wanna_be = {v}
+            while unnumbered:
+                v = _max_cardinality_node(C, unnumbered, numbered)
+                unnumbered.remove(v)
+                numbered.add(v)
+                new_clique_wanna_be = set(C.neighbors(v)) & numbered
+                sg = C.subgraph(clique_wanna_be)
+                if _is_complete_graph(sg):
+                    new_clique_wanna_be.add(v)
+                    if not new_clique_wanna_be >= clique_wanna_be:
+                        yield frozenset(clique_wanna_be)
+                    clique_wanna_be = new_clique_wanna_be
+                else:
+                    raise nx.NetworkXError("Input graph is not chordal.")
+            yield frozenset(clique_wanna_be)
+
+
+@nx._dispatchable
+def chordal_graph_treewidth(G):
+    """Returns the treewidth of the chordal graph G.
+
+    Parameters
+    ----------
+    G : graph
+      A NetworkX graph
+
+    Returns
+    -------
+    treewidth : int
+        The size of the largest clique in the graph minus one.
+
+    Raises
+    ------
+    NetworkXError
+        The algorithm does not support DiGraph, MultiGraph and MultiDiGraph.
+        The algorithm can only be applied to chordal graphs. If the input
+        graph is found to be non-chordal, a :exc:`NetworkXError` is raised.
+
+    Examples
+    --------
+    >>> e = [
+    ...     (1, 2),
+    ...     (1, 3),
+    ...     (2, 3),
+    ...     (2, 4),
+    ...     (3, 4),
+    ...     (3, 5),
+    ...     (3, 6),
+    ...     (4, 5),
+    ...     (4, 6),
+    ...     (5, 6),
+    ...     (7, 8),
+    ... ]
+    >>> G = nx.Graph(e)
+    >>> G.add_node(9)
+    >>> nx.chordal_graph_treewidth(G)
+    3
+
+    References
+    ----------
+    .. [1] https://en.wikipedia.org/wiki/Tree_decomposition#Treewidth
+    """
+    if not is_chordal(G):
+        raise nx.NetworkXError("Input graph is not chordal.")
+
+    max_clique = -1
+    for clique in nx.chordal_graph_cliques(G):
+        max_clique = max(max_clique, len(clique))
+    return max_clique - 1
+
+
+def _is_complete_graph(G):
+    """Returns True if G is a complete graph."""
+    if nx.number_of_selfloops(G) > 0:
+        raise nx.NetworkXError("Self loop found in _is_complete_graph()")
+    n = G.number_of_nodes()
+    if n < 2:
+        return True
+    e = G.number_of_edges()
+    max_edges = (n * (n - 1)) / 2
+    return e == max_edges
+
+
+def _find_missing_edge(G):
+    """Given a non-complete graph G, returns a missing edge."""
+    nodes = set(G)
+    for u in G:
+        missing = nodes - set(list(G[u].keys()) + [u])
+        if missing:
+            return (u, missing.pop())
+
+
+def _max_cardinality_node(G, choices, wanna_connect):
+    """Returns a the node in choices that has more connections in G
+    to nodes in wanna_connect.
+    """
+    max_number = -1
+    for x in choices:
+        number = len([y for y in G[x] if y in wanna_connect])
+        if number > max_number:
+            max_number = number
+            max_cardinality_node = x
+    return max_cardinality_node
+
+
+def _find_chordality_breaker(G, s=None, treewidth_bound=sys.maxsize):
+    """Given a graph G, starts a max cardinality search
+    (starting from s if s is given and from an arbitrary node otherwise)
+    trying to find a non-chordal cycle.
+
+    If it does find one, it returns (u,v,w) where u,v,w are the three
+    nodes that together with s are involved in the cycle.
+
+    It ignores any self loops.
+    """
+    if len(G) == 0:
+        raise nx.NetworkXPointlessConcept("Graph has no nodes.")
+    unnumbered = set(G)
+    if s is None:
+        s = arbitrary_element(G)
+    unnumbered.remove(s)
+    numbered = {s}
+    current_treewidth = -1
+    while unnumbered:  # and current_treewidth <= treewidth_bound:
+        v = _max_cardinality_node(G, unnumbered, numbered)
+        unnumbered.remove(v)
+        numbered.add(v)
+        clique_wanna_be = set(G[v]) & numbered
+        sg = G.subgraph(clique_wanna_be)
+        if _is_complete_graph(sg):
+            # The graph seems to be chordal by now. We update the treewidth
+            current_treewidth = max(current_treewidth, len(clique_wanna_be))
+            if current_treewidth > treewidth_bound:
+                raise nx.NetworkXTreewidthBoundExceeded(
+                    f"treewidth_bound exceeded: {current_treewidth}"
+                )
+        else:
+            # sg is not a clique,
+            # look for an edge that is not included in sg
+            (u, w) = _find_missing_edge(sg)
+            return (u, v, w)
+    return ()
+
+
+@not_implemented_for("directed")
+@nx._dispatchable(returns_graph=True)
+def complete_to_chordal_graph(G):
+    """Return a copy of G completed to a chordal graph
+
+    Adds edges to a copy of G to create a chordal graph. A graph G=(V,E) is
+    called chordal if for each cycle with length bigger than 3, there exist
+    two non-adjacent nodes connected by an edge (called a chord).
+
+    Parameters
+    ----------
+    G : NetworkX graph
+        Undirected graph
+
+    Returns
+    -------
+    H : NetworkX graph
+        The chordal enhancement of G
+    alpha : Dictionary
+            The elimination ordering of nodes of G
+
+    Notes
+    -----
+    There are different approaches to calculate the chordal
+    enhancement of a graph. The algorithm used here is called
+    MCS-M and gives at least minimal (local) triangulation of graph. Note
+    that this triangulation is not necessarily a global minimum.
+
+    https://en.wikipedia.org/wiki/Chordal_graph
+
+    References
+    ----------
+    .. [1] Berry, Anne & Blair, Jean & Heggernes, Pinar & Peyton, Barry. (2004)
+           Maximum Cardinality Search for Computing Minimal Triangulations of
+           Graphs.  Algorithmica. 39. 287-298. 10.1007/s00453-004-1084-3.
+
+    Examples
+    --------
+    >>> from networkx.algorithms.chordal import complete_to_chordal_graph
+    >>> G = nx.wheel_graph(10)
+    >>> H, alpha = complete_to_chordal_graph(G)
+    """
+    H = G.copy()
+    alpha = {node: 0 for node in H}
+    if nx.is_chordal(H):
+        return H, alpha
+    chords = set()
+    weight = {node: 0 for node in H.nodes()}
+    unnumbered_nodes = list(H.nodes())
+    for i in range(len(H.nodes()), 0, -1):
+        # get the node in unnumbered_nodes with the maximum weight
+        z = max(unnumbered_nodes, key=lambda node: weight[node])
+        unnumbered_nodes.remove(z)
+        alpha[z] = i
+        update_nodes = []
+        for y in unnumbered_nodes:
+            if G.has_edge(y, z):
+                update_nodes.append(y)
+            else:
+                # y_weight will be bigger than node weights between y and z
+                y_weight = weight[y]
+                lower_nodes = [
+                    node for node in unnumbered_nodes if weight[node] < y_weight
+                ]
+                if nx.has_path(H.subgraph(lower_nodes + [z, y]), y, z):
+                    update_nodes.append(y)
+                    chords.add((z, y))
+        # during calculation of paths the weights should not be updated
+        for node in update_nodes:
+            weight[node] += 1
+    H.add_edges_from(chords)
+    return H, alpha

venv/lib/python3.10/site-packages/networkx/algorithms/communicability_alg.py

@@ -0,0 +1,162 @@
+"""
+Communicability.
+"""
+import networkx as nx
+from networkx.utils import not_implemented_for
+
+__all__ = ["communicability", "communicability_exp"]
+
+
+@not_implemented_for("directed")
+@not_implemented_for("multigraph")
+@nx._dispatchable
+def communicability(G):
+    r"""Returns communicability between all pairs of nodes in G.
+
+    The communicability between pairs of nodes in G is the sum of
+    walks of different lengths starting at node u and ending at node v.
+
+    Parameters
+    ----------
+    G: graph
+
+    Returns
+    -------
+    comm: dictionary of dictionaries
+        Dictionary of dictionaries keyed by nodes with communicability
+        as the value.
+
+    Raises
+    ------
+    NetworkXError
+       If the graph is not undirected and simple.
+
+    See Also
+    --------
+    communicability_exp:
+       Communicability between all pairs of nodes in G  using spectral
+       decomposition.
+    communicability_betweenness_centrality:
+       Communicability betweenness centrality for each node in G.
+
+    Notes
+    -----
+    This algorithm uses a spectral decomposition of the adjacency matrix.
+    Let G=(V,E) be a simple undirected graph.  Using the connection between
+    the powers  of the adjacency matrix and the number of walks in the graph,
+    the communicability  between nodes `u` and `v` based on the graph spectrum
+    is [1]_
+
+    .. math::
+        C(u,v)=\sum_{j=1}^{n}\phi_{j}(u)\phi_{j}(v)e^{\lambda_{j}},
+
+    where `\phi_{j}(u)` is the `u\rm{th}` element of the `j\rm{th}` orthonormal
+    eigenvector of the adjacency matrix associated with the eigenvalue
+    `\lambda_{j}`.
+
+    References
+    ----------
+    .. [1] Ernesto Estrada, Naomichi Hatano,
+       "Communicability in complex networks",
+       Phys. Rev. E 77, 036111 (2008).
+       https://arxiv.org/abs/0707.0756
+
+    Examples
+    --------
+    >>> G = nx.Graph([(0, 1), (1, 2), (1, 5), (5, 4), (2, 4), (2, 3), (4, 3), (3, 6)])
+    >>> c = nx.communicability(G)
+    """
+    import numpy as np
+
+    nodelist = list(G)  # ordering of nodes in matrix
+    A = nx.to_numpy_array(G, nodelist)
+    # convert to 0-1 matrix
+    A[A != 0.0] = 1
+    w, vec = np.linalg.eigh(A)
+    expw = np.exp(w)
+    mapping = dict(zip(nodelist, range(len(nodelist))))
+    c = {}
+    # computing communicabilities
+    for u in G:
+        c[u] = {}
+        for v in G:
+            s = 0
+            p = mapping[u]
+            q = mapping[v]
+            for j in range(len(nodelist)):
+                s += vec[:, j][p] * vec[:, j][q] * expw[j]
+            c[u][v] = float(s)
+    return c
+
+
+@not_implemented_for("directed")
+@not_implemented_for("multigraph")
+@nx._dispatchable
+def communicability_exp(G):
+    r"""Returns communicability between all pairs of nodes in G.
+
+    Communicability between pair of node (u,v) of node in G is the sum of
+    walks of different lengths starting at node u and ending at node v.
+
+    Parameters
+    ----------
+    G: graph
+
+    Returns
+    -------
+    comm: dictionary of dictionaries
+        Dictionary of dictionaries keyed by nodes with communicability
+        as the value.
+
+    Raises
+    ------
+    NetworkXError
+        If the graph is not undirected and simple.
+
+    See Also
+    --------
+    communicability:
+       Communicability between pairs of nodes in G.
+    communicability_betweenness_centrality:
+       Communicability betweenness centrality for each node in G.
+
+    Notes
+    -----
+    This algorithm uses matrix exponentiation of the adjacency matrix.
+
+    Let G=(V,E) be a simple undirected graph.  Using the connection between
+    the powers  of the adjacency matrix and the number of walks in the graph,
+    the communicability between nodes u and v is [1]_,
+
+    .. math::
+        C(u,v) = (e^A)_{uv},
+
+    where `A` is the adjacency matrix of G.
+
+    References
+    ----------
+    .. [1] Ernesto Estrada, Naomichi Hatano,
+       "Communicability in complex networks",
+       Phys. Rev. E 77, 036111 (2008).
+       https://arxiv.org/abs/0707.0756
+
+    Examples
+    --------
+    >>> G = nx.Graph([(0, 1), (1, 2), (1, 5), (5, 4), (2, 4), (2, 3), (4, 3), (3, 6)])
+    >>> c = nx.communicability_exp(G)
+    """
+    import scipy as sp
+
+    nodelist = list(G)  # ordering of nodes in matrix
+    A = nx.to_numpy_array(G, nodelist)
+    # convert to 0-1 matrix
+    A[A != 0.0] = 1
+    # communicability matrix
+    expA = sp.linalg.expm(A)
+    mapping = dict(zip(nodelist, range(len(nodelist))))
+    c = {}
+    for u in G:
+        c[u] = {}
+        for v in G:
+            c[u][v] = float(expA[mapping[u], mapping[v]])
+    return c

venv/lib/python3.10/site-packages/networkx/algorithms/covering.py

@@ -0,0 +1,142 @@
+""" Functions related to graph covers."""
+
+from functools import partial
+from itertools import chain
+
+import networkx as nx
+from networkx.utils import arbitrary_element, not_implemented_for
+
+__all__ = ["min_edge_cover", "is_edge_cover"]
+
+
+@not_implemented_for("directed")
+@not_implemented_for("multigraph")
+@nx._dispatchable
+def min_edge_cover(G, matching_algorithm=None):
+    """Returns the min cardinality edge cover of the graph as a set of edges.
+
+    A smallest edge cover can be found in polynomial time by finding
+    a maximum matching and extending it greedily so that all nodes
+    are covered. This function follows that process. A maximum matching
+    algorithm can be specified for the first step of the algorithm.
+    The resulting set may return a set with one 2-tuple for each edge,
+    (the usual case) or with both 2-tuples `(u, v)` and `(v, u)` for
+    each edge. The latter is only done when a bipartite matching algorithm
+    is specified as `matching_algorithm`.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+        An undirected graph.
+
+    matching_algorithm : function
+        A function that returns a maximum cardinality matching for `G`.
+        The function must take one input, the graph `G`, and return
+        either a set of edges (with only one direction for the pair of nodes)
+        or a dictionary mapping each node to its mate. If not specified,
+        :func:`~networkx.algorithms.matching.max_weight_matching` is used.
+        Common bipartite matching functions include
+        :func:`~networkx.algorithms.bipartite.matching.hopcroft_karp_matching`
+        or
+        :func:`~networkx.algorithms.bipartite.matching.eppstein_matching`.
+
+    Returns
+    -------
+    min_cover : set
+
+        A set of the edges in a minimum edge cover in the form of tuples.
+        It contains only one of the equivalent 2-tuples `(u, v)` and `(v, u)`
+        for each edge. If a bipartite method is used to compute the matching,
+        the returned set contains both the 2-tuples `(u, v)` and `(v, u)`
+        for each edge of a minimum edge cover.
+
+    Examples
+    --------
+    >>> G = nx.Graph([(0, 1), (0, 2), (0, 3), (1, 2), (1, 3)])
+    >>> sorted(nx.min_edge_cover(G))
+    [(2, 1), (3, 0)]
+
+    Notes
+    -----
+    An edge cover of a graph is a set of edges such that every node of
+    the graph is incident to at least one edge of the set.
+    The minimum edge cover is an edge covering of smallest cardinality.
+
+    Due to its implementation, the worst-case running time of this algorithm
+    is bounded by the worst-case running time of the function
+    ``matching_algorithm``.
+
+    Minimum edge cover for `G` can also be found using the `min_edge_covering`
+    function in :mod:`networkx.algorithms.bipartite.covering` which is
+    simply this function with a default matching algorithm of
+    :func:`~networkx.algorithms.bipartite.matching.hopcraft_karp_matching`
+    """
+    if len(G) == 0:
+        return set()
+    if nx.number_of_isolates(G) > 0:
+        # ``min_cover`` does not exist as there is an isolated node
+        raise nx.NetworkXException(
+            "Graph has a node with no edge incident on it, so no edge cover exists."
+        )
+    if matching_algorithm is None:
+        matching_algorithm = partial(nx.max_weight_matching, maxcardinality=True)
+    maximum_matching = matching_algorithm(G)
+    # ``min_cover`` is superset of ``maximum_matching``
+    try:
+        # bipartite matching algs return dict so convert if needed
+        min_cover = set(maximum_matching.items())
+        bipartite_cover = True
+    except AttributeError:
+        min_cover = maximum_matching
+        bipartite_cover = False
+    # iterate for uncovered nodes
+    uncovered_nodes = set(G) - {v for u, v in min_cover} - {u for u, v in min_cover}
+    for v in uncovered_nodes:
+        # Since `v` is uncovered, each edge incident to `v` will join it
+        # with a covered node (otherwise, if there were an edge joining
+        # uncovered nodes `u` and `v`, the maximum matching algorithm
+        # would have found it), so we can choose an arbitrary edge
+        # incident to `v`. (This applies only in a simple graph, not a
+        # multigraph.)
+        u = arbitrary_element(G[v])
+        min_cover.add((u, v))
+        if bipartite_cover:
+            min_cover.add((v, u))
+    return min_cover
+
+
+@not_implemented_for("directed")
+@nx._dispatchable
+def is_edge_cover(G, cover):
+    """Decides whether a set of edges is a valid edge cover of the graph.
+
+    Given a set of edges, whether it is an edge covering can
+    be decided if we just check whether all nodes of the graph
+    has an edge from the set, incident on it.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+        An undirected bipartite graph.
+
+    cover : set
+        Set of edges to be checked.
+
+    Returns
+    -------
+    bool
+        Whether the set of edges is a valid edge cover of the graph.
+
+    Examples
+    --------
+    >>> G = nx.Graph([(0, 1), (0, 2), (0, 3), (1, 2), (1, 3)])
+    >>> cover = {(2, 1), (3, 0)}
+    >>> nx.is_edge_cover(G, cover)
+    True
+
+    Notes
+    -----
+    An edge cover of a graph is a set of edges such that every node of
+    the graph is incident to at least one edge of the set.
+    """
+    return set(G) <= set(chain.from_iterable(cover))

venv/lib/python3.10/site-packages/networkx/algorithms/distance_measures.py

@@ -0,0 +1,951 @@
+"""Graph diameter, radius, eccentricity and other properties."""
+
+import networkx as nx
+from networkx.utils import not_implemented_for
+
+__all__ = [
+    "eccentricity",
+    "diameter",
+    "radius",
+    "periphery",
+    "center",
+    "barycenter",
+    "resistance_distance",
+    "kemeny_constant",
+    "effective_graph_resistance",
+]
+
+
+def _extrema_bounding(G, compute="diameter", weight=None):
+    """Compute requested extreme distance metric of undirected graph G
+
+    Computation is based on smart lower and upper bounds, and in practice
+    linear in the number of nodes, rather than quadratic (except for some
+    border cases such as complete graphs or circle shaped graphs).
+
+    Parameters
+    ----------
+    G : NetworkX graph
+       An undirected graph
+
+    compute : string denoting the requesting metric
+       "diameter" for the maximal eccentricity value,
+       "radius" for the minimal eccentricity value,
+       "periphery" for the set of nodes with eccentricity equal to the diameter,
+       "center" for the set of nodes with eccentricity equal to the radius,
+       "eccentricities" for the maximum distance from each node to all other nodes in G
+
+    weight : string, function, or None
+        If this is a string, then edge weights will be accessed via the
+        edge attribute with this key (that is, the weight of the edge
+        joining `u` to `v` will be ``G.edges[u, v][weight]``). If no
+        such edge attribute exists, the weight of the edge is assumed to
+        be one.
+
+        If this is a function, the weight of an edge is the value
+        returned by the function. The function must accept exactly three
+        positional arguments: the two endpoints of an edge and the
+        dictionary of edge attributes for that edge. The function must
+        return a number.
+
+        If this is None, every edge has weight/distance/cost 1.
+
+        Weights stored as floating point values can lead to small round-off
+        errors in distances. Use integer weights to avoid this.
+
+        Weights should be positive, since they are distances.
+
+    Returns
+    -------
+    value : value of the requested metric
+       int for "diameter" and "radius" or
+       list of nodes for "center" and "periphery" or
+       dictionary of eccentricity values keyed by node for "eccentricities"
+
+    Raises
+    ------
+    NetworkXError
+        If the graph consists of multiple components
+    ValueError
+        If `compute` is not one of "diameter", "radius", "periphery", "center", or "eccentricities".
+
+    Notes
+    -----
+    This algorithm was proposed in [1]_ and discussed further in [2]_ and [3]_.
+
+    References
+    ----------
+    .. [1] F. W. Takes, W. A. Kosters,
+       "Determining the diameter of small world networks."
+       Proceedings of the 20th ACM international conference on Information and knowledge management, 2011
+       https://dl.acm.org/doi/abs/10.1145/2063576.2063748
+    .. [2] F. W. Takes, W. A. Kosters,
+       "Computing the Eccentricity Distribution of Large Graphs."
+       Algorithms, 2013
+       https://www.mdpi.com/1999-4893/6/1/100
+    .. [3] M. Borassi, P. Crescenzi, M. Habib, W. A. Kosters, A. Marino, F. W. Takes,
+       "Fast diameter and radius BFS-based computation in (weakly connected) real-world graphs: With an application to the six degrees of separation games. "
+       Theoretical Computer Science, 2015
+       https://www.sciencedirect.com/science/article/pii/S0304397515001644
+    """
+    # init variables
+    degrees = dict(G.degree())  # start with the highest degree node
+    minlowernode = max(degrees, key=degrees.get)
+    N = len(degrees)  # number of nodes
+    # alternate between smallest lower and largest upper bound
+    high = False
+    # status variables
+    ecc_lower = dict.fromkeys(G, 0)
+    ecc_upper = dict.fromkeys(G, N)
+    candidates = set(G)
+
+    # (re)set bound extremes
+    minlower = N
+    maxlower = 0
+    minupper = N
+    maxupper = 0
+
+    # repeat the following until there are no more candidates
+    while candidates:
+        if high:
+            current = maxuppernode  # select node with largest upper bound
+        else:
+            current = minlowernode  # select node with smallest lower bound
+        high = not high
+
+        # get distances from/to current node and derive eccentricity
+        dist = nx.shortest_path_length(G, source=current, weight=weight)
+
+        if len(dist) != N:
+            msg = "Cannot compute metric because graph is not connected."
+            raise nx.NetworkXError(msg)
+        current_ecc = max(dist.values())
+
+        # print status update
+        #        print ("ecc of " + str(current) + " (" + str(ecc_lower[current]) + "/"
+        #        + str(ecc_upper[current]) + ", deg: " + str(dist[current]) + ") is "
+        #        + str(current_ecc))
+        #        print(ecc_upper)
+
+        # (re)set bound extremes
+        maxuppernode = None
+        minlowernode = None
+
+        # update node bounds
+        for i in candidates:
+            # update eccentricity bounds
+            d = dist[i]
+            ecc_lower[i] = low = max(ecc_lower[i], max(d, (current_ecc - d)))
+            ecc_upper[i] = upp = min(ecc_upper[i], current_ecc + d)
+
+            # update min/max values of lower and upper bounds
+            minlower = min(ecc_lower[i], minlower)
+            maxlower = max(ecc_lower[i], maxlower)
+            minupper = min(ecc_upper[i], minupper)
+            maxupper = max(ecc_upper[i], maxupper)
+
+        # update candidate set
+        if compute == "diameter":
+            ruled_out = {
+                i
+                for i in candidates
+                if ecc_upper[i] <= maxlower and 2 * ecc_lower[i] >= maxupper
+            }
+        elif compute == "radius":
+            ruled_out = {
+                i
+                for i in candidates
+                if ecc_lower[i] >= minupper and ecc_upper[i] + 1 <= 2 * minlower
+            }
+        elif compute == "periphery":
+            ruled_out = {
+                i
+                for i in candidates
+                if ecc_upper[i] < maxlower
+                and (maxlower == maxupper or ecc_lower[i] > maxupper)
+            }
+        elif compute == "center":
+            ruled_out = {
+                i
+                for i in candidates
+                if ecc_lower[i] > minupper
+                and (minlower == minupper or ecc_upper[i] + 1 < 2 * minlower)
+            }
+        elif compute == "eccentricities":
+            ruled_out = set()
+        else:
+            msg = "compute must be one of 'diameter', 'radius', 'periphery', 'center', 'eccentricities'"
+            raise ValueError(msg)
+
+        ruled_out.update(i for i in candidates if ecc_lower[i] == ecc_upper[i])
+        candidates -= ruled_out
+
+        #        for i in ruled_out:
+        #            print("removing %g: ecc_u: %g maxl: %g ecc_l: %g maxu: %g"%
+        #                    (i,ecc_upper[i],maxlower,ecc_lower[i],maxupper))
+        #        print("node %g: ecc_u: %g maxl: %g ecc_l: %g maxu: %g"%
+        #                    (4,ecc_upper[4],maxlower,ecc_lower[4],maxupper))
+        #        print("NODE 4: %g"%(ecc_upper[4] <= maxlower))
+        #        print("NODE 4: %g"%(2 * ecc_lower[4] >= maxupper))
+        #        print("NODE 4: %g"%(ecc_upper[4] <= maxlower
+        #                            and 2 * ecc_lower[4] >= maxupper))
+
+        # updating maxuppernode and minlowernode for selection in next round
+        for i in candidates:
+            if (
+                minlowernode is None
+                or (
+                    ecc_lower[i] == ecc_lower[minlowernode]
+                    and degrees[i] > degrees[minlowernode]
+                )
+                or (ecc_lower[i] < ecc_lower[minlowernode])
+            ):
+                minlowernode = i
+
+            if (
+                maxuppernode is None
+                or (
+                    ecc_upper[i] == ecc_upper[maxuppernode]
+                    and degrees[i] > degrees[maxuppernode]
+                )
+                or (ecc_upper[i] > ecc_upper[maxuppernode])
+            ):
+                maxuppernode = i
+
+        # print status update
+    #        print (" min=" + str(minlower) + "/" + str(minupper) +
+    #        " max=" + str(maxlower) + "/" + str(maxupper) +
+    #        " candidates: " + str(len(candidates)))
+    #        print("cand:",candidates)
+    #        print("ecc_l",ecc_lower)
+    #        print("ecc_u",ecc_upper)
+    #        wait = input("press Enter to continue")
+
+    # return the correct value of the requested metric
+    if compute == "diameter":
+        return maxlower
+    if compute == "radius":
+        return minupper
+    if compute == "periphery":
+        p = [v for v in G if ecc_lower[v] == maxlower]
+        return p
+    if compute == "center":
+        c = [v for v in G if ecc_upper[v] == minupper]
+        return c
+    if compute == "eccentricities":
+        return ecc_lower
+    return None
+
+
+@nx._dispatchable(edge_attrs="weight")
+def eccentricity(G, v=None, sp=None, weight=None):
+    """Returns the eccentricity of nodes in G.
+
+    The eccentricity of a node v is the maximum distance from v to
+    all other nodes in G.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+       A graph
+
+    v : node, optional
+       Return value of specified node
+
+    sp : dict of dicts, optional
+       All pairs shortest path lengths as a dictionary of dictionaries
+
+    weight : string, function, or None (default=None)
+        If this is a string, then edge weights will be accessed via the
+        edge attribute with this key (that is, the weight of the edge
+        joining `u` to `v` will be ``G.edges[u, v][weight]``). If no
+        such edge attribute exists, the weight of the edge is assumed to
+        be one.
+
+        If this is a function, the weight of an edge is the value
+        returned by the function. The function must accept exactly three
+        positional arguments: the two endpoints of an edge and the
+        dictionary of edge attributes for that edge. The function must
+        return a number.
+
+        If this is None, every edge has weight/distance/cost 1.
+
+        Weights stored as floating point values can lead to small round-off
+        errors in distances. Use integer weights to avoid this.
+
+        Weights should be positive, since they are distances.
+
+    Returns
+    -------
+    ecc : dictionary
+       A dictionary of eccentricity values keyed by node.
+
+    Examples
+    --------
+    >>> G = nx.Graph([(1, 2), (1, 3), (1, 4), (3, 4), (3, 5), (4, 5)])
+    >>> dict(nx.eccentricity(G))
+    {1: 2, 2: 3, 3: 2, 4: 2, 5: 3}
+
+    >>> dict(nx.eccentricity(G, v=[1, 5]))  # This returns the eccentricity of node 1 & 5
+    {1: 2, 5: 3}
+
+    """
+    #    if v is None:                # none, use entire graph
+    #        nodes=G.nodes()
+    #    elif v in G:               # is v a single node
+    #        nodes=[v]
+    #    else:                      # assume v is a container of nodes
+    #        nodes=v
+    order = G.order()
+    e = {}
+    for n in G.nbunch_iter(v):
+        if sp is None:
+            length = nx.shortest_path_length(G, source=n, weight=weight)
+
+            L = len(length)
+        else:
+            try:
+                length = sp[n]
+                L = len(length)
+            except TypeError as err:
+                raise nx.NetworkXError('Format of "sp" is invalid.') from err
+        if L != order:
+            if G.is_directed():
+                msg = (
+                    "Found infinite path length because the digraph is not"
+                    " strongly connected"
+                )
+            else:
+                msg = "Found infinite path length because the graph is not" " connected"
+            raise nx.NetworkXError(msg)
+
+        e[n] = max(length.values())
+
+    if v in G:
+        return e[v]  # return single value
+    return e
+
+
+@nx._dispatchable(edge_attrs="weight")
+def diameter(G, e=None, usebounds=False, weight=None):
+    """Returns the diameter of the graph G.
+
+    The diameter is the maximum eccentricity.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+       A graph
+
+    e : eccentricity dictionary, optional
+      A precomputed dictionary of eccentricities.
+
+    weight : string, function, or None
+        If this is a string, then edge weights will be accessed via the
+        edge attribute with this key (that is, the weight of the edge
+        joining `u` to `v` will be ``G.edges[u, v][weight]``). If no
+        such edge attribute exists, the weight of the edge is assumed to
+        be one.
+
+        If this is a function, the weight of an edge is the value
+        returned by the function. The function must accept exactly three
+        positional arguments: the two endpoints of an edge and the
+        dictionary of edge attributes for that edge. The function must
+        return a number.
+
+        If this is None, every edge has weight/distance/cost 1.
+
+        Weights stored as floating point values can lead to small round-off
+        errors in distances. Use integer weights to avoid this.
+
+        Weights should be positive, since they are distances.
+
+    Returns
+    -------
+    d : integer
+       Diameter of graph
+
+    Examples
+    --------
+    >>> G = nx.Graph([(1, 2), (1, 3), (1, 4), (3, 4), (3, 5), (4, 5)])
+    >>> nx.diameter(G)
+    3
+
+    See Also
+    --------
+    eccentricity
+    """
+    if usebounds is True and e is None and not G.is_directed():
+        return _extrema_bounding(G, compute="diameter", weight=weight)
+    if e is None:
+        e = eccentricity(G, weight=weight)
+    return max(e.values())
+
+
+@nx._dispatchable(edge_attrs="weight")
+def periphery(G, e=None, usebounds=False, weight=None):
+    """Returns the periphery of the graph G.
+
+    The periphery is the set of nodes with eccentricity equal to the diameter.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+       A graph
+
+    e : eccentricity dictionary, optional
+      A precomputed dictionary of eccentricities.
+
+    weight : string, function, or None
+        If this is a string, then edge weights will be accessed via the
+        edge attribute with this key (that is, the weight of the edge
+        joining `u` to `v` will be ``G.edges[u, v][weight]``). If no
+        such edge attribute exists, the weight of the edge is assumed to
+        be one.
+
+        If this is a function, the weight of an edge is the value
+        returned by the function. The function must accept exactly three
+        positional arguments: the two endpoints of an edge and the
+        dictionary of edge attributes for that edge. The function must
+        return a number.
+
+        If this is None, every edge has weight/distance/cost 1.
+
+        Weights stored as floating point values can lead to small round-off
+        errors in distances. Use integer weights to avoid this.
+
+        Weights should be positive, since they are distances.
+
+    Returns
+    -------
+    p : list
+       List of nodes in periphery
+
+    Examples
+    --------
+    >>> G = nx.Graph([(1, 2), (1, 3), (1, 4), (3, 4), (3, 5), (4, 5)])
+    >>> nx.periphery(G)
+    [2, 5]
+
+    See Also
+    --------
+    barycenter
+    center
+    """
+    if usebounds is True and e is None and not G.is_directed():
+        return _extrema_bounding(G, compute="periphery", weight=weight)
+    if e is None:
+        e = eccentricity(G, weight=weight)
+    diameter = max(e.values())
+    p = [v for v in e if e[v] == diameter]
+    return p
+
+
+@nx._dispatchable(edge_attrs="weight")
+def radius(G, e=None, usebounds=False, weight=None):
+    """Returns the radius of the graph G.
+
+    The radius is the minimum eccentricity.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+       A graph
+
+    e : eccentricity dictionary, optional
+      A precomputed dictionary of eccentricities.
+
+    weight : string, function, or None
+        If this is a string, then edge weights will be accessed via the
+        edge attribute with this key (that is, the weight of the edge
+        joining `u` to `v` will be ``G.edges[u, v][weight]``). If no
+        such edge attribute exists, the weight of the edge is assumed to
+        be one.
+
+        If this is a function, the weight of an edge is the value
+        returned by the function. The function must accept exactly three
+        positional arguments: the two endpoints of an edge and the
+        dictionary of edge attributes for that edge. The function must
+        return a number.
+
+        If this is None, every edge has weight/distance/cost 1.
+
+        Weights stored as floating point values can lead to small round-off
+        errors in distances. Use integer weights to avoid this.
+
+        Weights should be positive, since they are distances.
+
+    Returns
+    -------
+    r : integer
+       Radius of graph
+
+    Examples
+    --------
+    >>> G = nx.Graph([(1, 2), (1, 3), (1, 4), (3, 4), (3, 5), (4, 5)])
+    >>> nx.radius(G)
+    2
+
+    """
+    if usebounds is True and e is None and not G.is_directed():
+        return _extrema_bounding(G, compute="radius", weight=weight)
+    if e is None:
+        e = eccentricity(G, weight=weight)
+    return min(e.values())
+
+
+@nx._dispatchable(edge_attrs="weight")
+def center(G, e=None, usebounds=False, weight=None):
+    """Returns the center of the graph G.
+
+    The center is the set of nodes with eccentricity equal to radius.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+       A graph
+
+    e : eccentricity dictionary, optional
+      A precomputed dictionary of eccentricities.
+
+    weight : string, function, or None
+        If this is a string, then edge weights will be accessed via the
+        edge attribute with this key (that is, the weight of the edge
+        joining `u` to `v` will be ``G.edges[u, v][weight]``). If no
+        such edge attribute exists, the weight of the edge is assumed to
+        be one.
+
+        If this is a function, the weight of an edge is the value
+        returned by the function. The function must accept exactly three
+        positional arguments: the two endpoints of an edge and the
+        dictionary of edge attributes for that edge. The function must
+        return a number.
+
+        If this is None, every edge has weight/distance/cost 1.
+
+        Weights stored as floating point values can lead to small round-off
+        errors in distances. Use integer weights to avoid this.
+
+        Weights should be positive, since they are distances.
+
+    Returns
+    -------
+    c : list
+       List of nodes in center
+
+    Examples
+    --------
+    >>> G = nx.Graph([(1, 2), (1, 3), (1, 4), (3, 4), (3, 5), (4, 5)])
+    >>> list(nx.center(G))
+    [1, 3, 4]
+
+    See Also
+    --------
+    barycenter
+    periphery
+    """
+    if usebounds is True and e is None and not G.is_directed():
+        return _extrema_bounding(G, compute="center", weight=weight)
+    if e is None:
+        e = eccentricity(G, weight=weight)
+    radius = min(e.values())
+    p = [v for v in e if e[v] == radius]
+    return p
+
+
+@nx._dispatchable(edge_attrs="weight", mutates_input={"attr": 2})
+def barycenter(G, weight=None, attr=None, sp=None):
+    r"""Calculate barycenter of a connected graph, optionally with edge weights.
+
+    The :dfn:`barycenter` a
+    :func:`connected <networkx.algorithms.components.is_connected>` graph
+    :math:`G` is the subgraph induced by the set of its nodes :math:`v`
+    minimizing the objective function
+
+    .. math::
+
+        \sum_{u \in V(G)} d_G(u, v),
+
+    where :math:`d_G` is the (possibly weighted) :func:`path length
+    <networkx.algorithms.shortest_paths.generic.shortest_path_length>`.
+    The barycenter is also called the :dfn:`median`. See [West01]_, p. 78.
+
+    Parameters
+    ----------
+    G : :class:`networkx.Graph`
+        The connected graph :math:`G`.
+    weight : :class:`str`, optional
+        Passed through to
+        :func:`~networkx.algorithms.shortest_paths.generic.shortest_path_length`.
+    attr : :class:`str`, optional
+        If given, write the value of the objective function to each node's
+        `attr` attribute. Otherwise do not store the value.
+    sp : dict of dicts, optional
+       All pairs shortest path lengths as a dictionary of dictionaries
+
+    Returns
+    -------
+    list
+        Nodes of `G` that induce the barycenter of `G`.
+
+    Raises
+    ------
+    NetworkXNoPath
+        If `G` is disconnected. `G` may appear disconnected to
+        :func:`barycenter` if `sp` is given but is missing shortest path
+        lengths for any pairs.
+    ValueError
+        If `sp` and `weight` are both given.
+
+    Examples
+    --------
+    >>> G = nx.Graph([(1, 2), (1, 3), (1, 4), (3, 4), (3, 5), (4, 5)])
+    >>> nx.barycenter(G)
+    [1, 3, 4]
+
+    See Also
+    --------
+    center
+    periphery
+    """
+    if sp is None:
+        sp = nx.shortest_path_length(G, weight=weight)
+    else:
+        sp = sp.items()
+        if weight is not None:
+            raise ValueError("Cannot use both sp, weight arguments together")
+    smallest, barycenter_vertices, n = float("inf"), [], len(G)
+    for v, dists in sp:
+        if len(dists) < n:
+            raise nx.NetworkXNoPath(
+                f"Input graph {G} is disconnected, so every induced subgraph "
+                "has infinite barycentricity."
+            )
+        barycentricity = sum(dists.values())
+        if attr is not None:
+            G.nodes[v][attr] = barycentricity
+        if barycentricity < smallest:
+            smallest = barycentricity
+            barycenter_vertices = [v]
+        elif barycentricity == smallest:
+            barycenter_vertices.append(v)
+    if attr is not None:
+        nx._clear_cache(G)
+    return barycenter_vertices
+
+
+@not_implemented_for("directed")
+@nx._dispatchable(edge_attrs="weight")
+def resistance_distance(G, nodeA=None, nodeB=None, weight=None, invert_weight=True):
+    """Returns the resistance distance between pairs of nodes in graph G.
+
+    The resistance distance between two nodes of a graph is akin to treating
+    the graph as a grid of resistors with a resistance equal to the provided
+    weight [1]_, [2]_.
+
+    If weight is not provided, then a weight of 1 is used for all edges.
+
+    If two nodes are the same, the resistance distance is zero.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+       A graph
+
+    nodeA : node or None, optional (default=None)
+      A node within graph G.
+      If None, compute resistance distance using all nodes as source nodes.
+
+    nodeB : node or None, optional (default=None)
+      A node within graph G.
+      If None, compute resistance distance using all nodes as target nodes.
+
+    weight : string or None, optional (default=None)
+       The edge data key used to compute the resistance distance.
+       If None, then each edge has weight 1.
+
+    invert_weight : boolean (default=True)
+        Proper calculation of resistance distance requires building the
+        Laplacian matrix with the reciprocal of the weight. Not required
+        if the weight is already inverted. Weight cannot be zero.
+
+    Returns
+    -------
+    rd : dict or float
+       If `nodeA` and `nodeB` are given, resistance distance between `nodeA`
+       and `nodeB`. If `nodeA` or `nodeB` is unspecified (the default), a
+       dictionary of nodes with resistance distances as the value.
+
+    Raises
+    ------
+    NetworkXNotImplemented
+        If `G` is a directed graph.
+
+    NetworkXError
+        If `G` is not connected, or contains no nodes,
+        or `nodeA` is not in `G` or `nodeB` is not in `G`.
+
+    Examples
+    --------
+    >>> G = nx.Graph([(1, 2), (1, 3), (1, 4), (3, 4), (3, 5), (4, 5)])
+    >>> round(nx.resistance_distance(G, 1, 3), 10)
+    0.625
+
+    Notes
+    -----
+    The implementation is based on Theorem A in [2]_. Self-loops are ignored.
+    Multi-edges are contracted in one edge with weight equal to the harmonic sum of the weights.
+
+    References
+    ----------
+    .. [1] Wikipedia
+       "Resistance distance."
+       https://en.wikipedia.org/wiki/Resistance_distance
+    .. [2] D. J. Klein and M. Randic.
+        Resistance distance.
+        J. of Math. Chem. 12:81-95, 1993.
+    """
+    import numpy as np
+
+    if len(G) == 0:
+        raise nx.NetworkXError("Graph G must contain at least one node.")
+    if not nx.is_connected(G):
+        raise nx.NetworkXError("Graph G must be strongly connected.")
+    if nodeA is not None and nodeA not in G:
+        raise nx.NetworkXError("Node A is not in graph G.")
+    if nodeB is not None and nodeB not in G:
+        raise nx.NetworkXError("Node B is not in graph G.")
+
+    G = G.copy()
+    node_list = list(G)
+
+    # Invert weights
+    if invert_weight and weight is not None:
+        if G.is_multigraph():
+            for u, v, k, d in G.edges(keys=True, data=True):
+                d[weight] = 1 / d[weight]
+        else:
+            for u, v, d in G.edges(data=True):
+                d[weight] = 1 / d[weight]
+
+    # Compute resistance distance using the Pseudo-inverse of the Laplacian
+    # Self-loops are ignored
+    L = nx.laplacian_matrix(G, weight=weight).todense()
+    Linv = np.linalg.pinv(L, hermitian=True)
+
+    # Return relevant distances
+    if nodeA is not None and nodeB is not None:
+        i = node_list.index(nodeA)
+        j = node_list.index(nodeB)
+        return Linv.item(i, i) + Linv.item(j, j) - Linv.item(i, j) - Linv.item(j, i)
+
+    elif nodeA is not None:
+        i = node_list.index(nodeA)
+        d = {}
+        for n in G:
+            j = node_list.index(n)
+            d[n] = Linv.item(i, i) + Linv.item(j, j) - Linv.item(i, j) - Linv.item(j, i)
+        return d
+
+    elif nodeB is not None:
+        j = node_list.index(nodeB)
+        d = {}
+        for n in G:
+            i = node_list.index(n)
+            d[n] = Linv.item(i, i) + Linv.item(j, j) - Linv.item(i, j) - Linv.item(j, i)
+        return d
+
+    else:
+        d = {}
+        for n in G:
+            i = node_list.index(n)
+            d[n] = {}
+            for n2 in G:
+                j = node_list.index(n2)
+                d[n][n2] = (
+                    Linv.item(i, i)
+                    + Linv.item(j, j)
+                    - Linv.item(i, j)
+                    - Linv.item(j, i)
+                )
+        return d
+
+
+@not_implemented_for("directed")
+@nx._dispatchable(edge_attrs="weight")
+def effective_graph_resistance(G, weight=None, invert_weight=True):
+    """Returns the Effective graph resistance of G.
+
+    Also known as the Kirchhoff index.
+
+    The effective graph resistance is defined as the sum
+    of the resistance distance of every node pair in G [1]_.
+
+    If weight is not provided, then a weight of 1 is used for all edges.
+
+    The effective graph resistance of a disconnected graph is infinite.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+       A graph
+
+    weight : string or None, optional (default=None)
+       The edge data key used to compute the effective graph resistance.
+       If None, then each edge has weight 1.
+
+    invert_weight : boolean (default=True)
+        Proper calculation of resistance distance requires building the
+        Laplacian matrix with the reciprocal of the weight. Not required
+        if the weight is already inverted. Weight cannot be zero.
+
+    Returns
+    -------
+    RG : float
+        The effective graph resistance of `G`.
+
+    Raises
+    ------
+    NetworkXNotImplemented
+        If `G` is a directed graph.
+
+    NetworkXError
+        If `G` does not contain any nodes.
+
+    Examples
+    --------
+    >>> G = nx.Graph([(1, 2), (1, 3), (1, 4), (3, 4), (3, 5), (4, 5)])
+    >>> round(nx.effective_graph_resistance(G), 10)
+    10.25
+
+    Notes
+    -----
+    The implementation is based on Theorem 2.2 in [2]_. Self-loops are ignored.
+    Multi-edges are contracted in one edge with weight equal to the harmonic sum of the weights.
+
+    References
+    ----------
+    .. [1] Wolfram
+       "Kirchhoff Index."
+       https://mathworld.wolfram.com/KirchhoffIndex.html
+    .. [2] W. Ellens, F. M. Spieksma, P. Van Mieghem, A. Jamakovic, R. E. Kooij.
+        Effective graph resistance.
+        Lin. Alg. Appl. 435:2491-2506, 2011.
+    """
+    import numpy as np
+
+    if len(G) == 0:
+        raise nx.NetworkXError("Graph G must contain at least one node.")
+
+    # Disconnected graphs have infinite Effective graph resistance
+    if not nx.is_connected(G):
+        return float("inf")
+
+    # Invert weights
+    G = G.copy()
+    if invert_weight and weight is not None:
+        if G.is_multigraph():
+            for u, v, k, d in G.edges(keys=True, data=True):
+                d[weight] = 1 / d[weight]
+        else:
+            for u, v, d in G.edges(data=True):
+                d[weight] = 1 / d[weight]
+
+    # Get Laplacian eigenvalues
+    mu = np.sort(nx.laplacian_spectrum(G, weight=weight))
+
+    # Compute Effective graph resistance based on spectrum of the Laplacian
+    # Self-loops are ignored
+    return float(np.sum(1 / mu[1:]) * G.number_of_nodes())
+
+
+@nx.utils.not_implemented_for("directed")
+@nx._dispatchable(edge_attrs="weight")
+def kemeny_constant(G, *, weight=None):
+    """Returns the Kemeny constant of the given graph.
+
+    The *Kemeny constant* (or Kemeny's constant) of a graph `G`
+    can be computed by regarding the graph as a Markov chain.
+    The Kemeny constant is then the expected number of time steps
+    to transition from a starting state i to a random destination state
+    sampled from the Markov chain's stationary distribution.
+    The Kemeny constant is independent of the chosen initial state [1]_.
+
+    The Kemeny constant measures the time needed for spreading
+    across a graph. Low values indicate a closely connected graph
+    whereas high values indicate a spread-out graph.
+
+    If weight is not provided, then a weight of 1 is used for all edges.
+
+    Since `G` represents a Markov chain, the weights must be positive.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+
+    weight : string or None, optional (default=None)
+       The edge data key used to compute the Kemeny constant.
+       If None, then each edge has weight 1.
+
+    Returns
+    -------
+    float
+        The Kemeny constant of the graph `G`.
+
+    Raises
+    ------
+    NetworkXNotImplemented
+        If the graph `G` is directed.
+
+    NetworkXError
+        If the graph `G` is not connected, or contains no nodes,
+        or has edges with negative weights.
+
+    Examples
+    --------
+    >>> G = nx.complete_graph(5)
+    >>> round(nx.kemeny_constant(G), 10)
+    3.2
+
+    Notes
+    -----
+    The implementation is based on equation (3.3) in [2]_.
+    Self-loops are allowed and indicate a Markov chain where
+    the state can remain the same. Multi-edges are contracted
+    in one edge with weight equal to the sum of the weights.
+
+    References
+    ----------
+    .. [1] Wikipedia
+       "Kemeny's constant."
+       https://en.wikipedia.org/wiki/Kemeny%27s_constant
+    .. [2] Lovász L.
+        Random walks on graphs: A survey.
+        Paul Erdös is Eighty, vol. 2, Bolyai Society,
+        Mathematical Studies, Keszthely, Hungary (1993), pp. 1-46
+    """
+    import numpy as np
+    import scipy as sp
+
+    if len(G) == 0:
+        raise nx.NetworkXError("Graph G must contain at least one node.")
+    if not nx.is_connected(G):
+        raise nx.NetworkXError("Graph G must be connected.")
+    if nx.is_negatively_weighted(G, weight=weight):
+        raise nx.NetworkXError("The weights of graph G must be nonnegative.")
+
+    # Compute matrix H = D^-1/2 A D^-1/2
+    A = nx.adjacency_matrix(G, weight=weight)
+    n, m = A.shape
+    diags = A.sum(axis=1)
+    with np.errstate(divide="ignore"):
+        diags_sqrt = 1.0 / np.sqrt(diags)
+    diags_sqrt[np.isinf(diags_sqrt)] = 0
+    DH = sp.sparse.csr_array(sp.sparse.spdiags(diags_sqrt, 0, m, n, format="csr"))
+    H = DH @ (A @ DH)
+
+    # Compute eigenvalues of H
+    eig = np.sort(sp.linalg.eigvalsh(H.todense()))
+
+    # Compute the Kemeny constant
+    return float(np.sum(1 / (1 - eig[:-1])))

venv/lib/python3.10/site-packages/networkx/algorithms/distance_regular.py

@@ -0,0 +1,238 @@
+"""
+=======================
+Distance-regular graphs
+=======================
+"""
+
+import networkx as nx
+from networkx.utils import not_implemented_for
+
+from .distance_measures import diameter
+
+__all__ = [
+    "is_distance_regular",
+    "is_strongly_regular",
+    "intersection_array",
+    "global_parameters",
+]
+
+
+@nx._dispatchable
+def is_distance_regular(G):
+    """Returns True if the graph is distance regular, False otherwise.
+
+    A connected graph G is distance-regular if for any nodes x,y
+    and any integers i,j=0,1,...,d (where d is the graph
+    diameter), the number of vertices at distance i from x and
+    distance j from y depends only on i,j and the graph distance
+    between x and y, independently of the choice of x and y.
+
+    Parameters
+    ----------
+    G: Networkx graph (undirected)
+
+    Returns
+    -------
+    bool
+      True if the graph is Distance Regular, False otherwise
+
+    Examples
+    --------
+    >>> G = nx.hypercube_graph(6)
+    >>> nx.is_distance_regular(G)
+    True
+
+    See Also
+    --------
+    intersection_array, global_parameters
+
+    Notes
+    -----
+    For undirected and simple graphs only
+
+    References
+    ----------
+    .. [1] Brouwer, A. E.; Cohen, A. M.; and Neumaier, A.
+        Distance-Regular Graphs. New York: Springer-Verlag, 1989.
+    .. [2] Weisstein, Eric W. "Distance-Regular Graph."
+        http://mathworld.wolfram.com/Distance-RegularGraph.html
+
+    """
+    try:
+        intersection_array(G)
+        return True
+    except nx.NetworkXError:
+        return False
+
+
+def global_parameters(b, c):
+    """Returns global parameters for a given intersection array.
+
+    Given a distance-regular graph G with integers b_i, c_i,i = 0,....,d
+    such that for any 2 vertices x,y in G at a distance i=d(x,y), there
+    are exactly c_i neighbors of y at a distance of i-1 from x and b_i
+    neighbors of y at a distance of i+1 from x.
+
+    Thus, a distance regular graph has the global parameters,
+    [[c_0,a_0,b_0],[c_1,a_1,b_1],......,[c_d,a_d,b_d]] for the
+    intersection array  [b_0,b_1,.....b_{d-1};c_1,c_2,.....c_d]
+    where a_i+b_i+c_i=k , k= degree of every vertex.
+
+    Parameters
+    ----------
+    b : list
+
+    c : list
+
+    Returns
+    -------
+    iterable
+       An iterable over three tuples.
+
+    Examples
+    --------
+    >>> G = nx.dodecahedral_graph()
+    >>> b, c = nx.intersection_array(G)
+    >>> list(nx.global_parameters(b, c))
+    [(0, 0, 3), (1, 0, 2), (1, 1, 1), (1, 1, 1), (2, 0, 1), (3, 0, 0)]
+
+    References
+    ----------
+    .. [1] Weisstein, Eric W. "Global Parameters."
+       From MathWorld--A Wolfram Web Resource.
+       http://mathworld.wolfram.com/GlobalParameters.html
+
+    See Also
+    --------
+    intersection_array
+    """
+    return ((y, b[0] - x - y, x) for x, y in zip(b + [0], [0] + c))
+
+
+@not_implemented_for("directed")
+@not_implemented_for("multigraph")
+@nx._dispatchable
+def intersection_array(G):
+    """Returns the intersection array of a distance-regular graph.
+
+    Given a distance-regular graph G with integers b_i, c_i,i = 0,....,d
+    such that for any 2 vertices x,y in G at a distance i=d(x,y), there
+    are exactly c_i neighbors of y at a distance of i-1 from x and b_i
+    neighbors of y at a distance of i+1 from x.
+
+    A distance regular graph's intersection array is given by,
+    [b_0,b_1,.....b_{d-1};c_1,c_2,.....c_d]
+
+    Parameters
+    ----------
+    G: Networkx graph (undirected)
+
+    Returns
+    -------
+    b,c: tuple of lists
+
+    Examples
+    --------
+    >>> G = nx.icosahedral_graph()
+    >>> nx.intersection_array(G)
+    ([5, 2, 1], [1, 2, 5])
+
+    References
+    ----------
+    .. [1] Weisstein, Eric W. "Intersection Array."
+       From MathWorld--A Wolfram Web Resource.
+       http://mathworld.wolfram.com/IntersectionArray.html
+
+    See Also
+    --------
+    global_parameters
+    """
+    # test for regular graph (all degrees must be equal)
+    if len(G) == 0:
+        raise nx.NetworkXPointlessConcept("Graph has no nodes.")
+    degree = iter(G.degree())
+    (_, k) = next(degree)
+    for _, knext in degree:
+        if knext != k:
+            raise nx.NetworkXError("Graph is not distance regular.")
+        k = knext
+    path_length = dict(nx.all_pairs_shortest_path_length(G))
+    diameter = max(max(path_length[n].values()) for n in path_length)
+    bint = {}  # 'b' intersection array
+    cint = {}  # 'c' intersection array
+    for u in G:
+        for v in G:
+            try:
+                i = path_length[u][v]
+            except KeyError as err:  # graph must be connected
+                raise nx.NetworkXError("Graph is not distance regular.") from err
+            # number of neighbors of v at a distance of i-1 from u
+            c = len([n for n in G[v] if path_length[n][u] == i - 1])
+            # number of neighbors of v at a distance of i+1 from u
+            b = len([n for n in G[v] if path_length[n][u] == i + 1])
+            # b,c are independent of u and v
+            if cint.get(i, c) != c or bint.get(i, b) != b:
+                raise nx.NetworkXError("Graph is not distance regular")
+            bint[i] = b
+            cint[i] = c
+    return (
+        [bint.get(j, 0) for j in range(diameter)],
+        [cint.get(j + 1, 0) for j in range(diameter)],
+    )
+
+
+# TODO There is a definition for directed strongly regular graphs.
+@not_implemented_for("directed")
+@not_implemented_for("multigraph")
+@nx._dispatchable
+def is_strongly_regular(G):
+    """Returns True if and only if the given graph is strongly
+    regular.
+
+    An undirected graph is *strongly regular* if
+
+    * it is regular,
+    * each pair of adjacent vertices has the same number of neighbors in
+      common,
+    * each pair of nonadjacent vertices has the same number of neighbors
+      in common.
+
+    Each strongly regular graph is a distance-regular graph.
+    Conversely, if a distance-regular graph has diameter two, then it is
+    a strongly regular graph. For more information on distance-regular
+    graphs, see :func:`is_distance_regular`.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+        An undirected graph.
+
+    Returns
+    -------
+    bool
+        Whether `G` is strongly regular.
+
+    Examples
+    --------
+
+    The cycle graph on five vertices is strongly regular. It is
+    two-regular, each pair of adjacent vertices has no shared neighbors,
+    and each pair of nonadjacent vertices has one shared neighbor::
+
+        >>> G = nx.cycle_graph(5)
+        >>> nx.is_strongly_regular(G)
+        True
+
+    """
+    # Here is an alternate implementation based directly on the
+    # definition of strongly regular graphs:
+    #
+    #     return (all_equal(G.degree().values())
+    #             and all_equal(len(common_neighbors(G, u, v))
+    #                           for u, v in G.edges())
+    #             and all_equal(len(common_neighbors(G, u, v))
+    #                           for u, v in non_edges(G)))
+    #
+    # We instead use the fact that a distance-regular graph of diameter
+    # two is strongly regular.
+    return is_distance_regular(G) and diameter(G) == 2

venv/lib/python3.10/site-packages/networkx/algorithms/hierarchy.py

@@ -0,0 +1,48 @@
+"""
+Flow Hierarchy.
+"""
+import networkx as nx
+
+__all__ = ["flow_hierarchy"]
+
+
+@nx._dispatchable(edge_attrs="weight")
+def flow_hierarchy(G, weight=None):
+    """Returns the flow hierarchy of a directed network.
+
+    Flow hierarchy is defined as the fraction of edges not participating
+    in cycles in a directed graph [1]_.
+
+    Parameters
+    ----------
+    G : DiGraph or MultiDiGraph
+       A directed graph
+
+    weight : string, optional (default=None)
+       Attribute to use for edge weights. If None the weight defaults to 1.
+
+    Returns
+    -------
+    h : float
+       Flow hierarchy value
+
+    Notes
+    -----
+    The algorithm described in [1]_ computes the flow hierarchy through
+    exponentiation of the adjacency matrix.  This function implements an
+    alternative approach that finds strongly connected components.
+    An edge is in a cycle if and only if it is in a strongly connected
+    component, which can be found in $O(m)$ time using Tarjan's algorithm.
+
+    References
+    ----------
+    .. [1] Luo, J.; Magee, C.L. (2011),
+       Detecting evolving patterns of self-organizing networks by flow
+       hierarchy measurement, Complexity, Volume 16 Issue 6 53-61.
+       DOI: 10.1002/cplx.20368
+       http://web.mit.edu/~cmagee/www/documents/28-DetectingEvolvingPatterns_FlowHierarchy.pdf
+    """
+    if not G.is_directed():
+        raise nx.NetworkXError("G must be a digraph in flow_hierarchy")
+    scc = nx.strongly_connected_components(G)
+    return 1 - sum(G.subgraph(c).size(weight) for c in scc) / G.size(weight)

venv/lib/python3.10/site-packages/networkx/algorithms/isolate.py

@@ -0,0 +1,107 @@
+"""
+Functions for identifying isolate (degree zero) nodes.
+"""
+import networkx as nx
+
+__all__ = ["is_isolate", "isolates", "number_of_isolates"]
+
+
+@nx._dispatchable
+def is_isolate(G, n):
+    """Determines whether a node is an isolate.
+
+    An *isolate* is a node with no neighbors (that is, with degree
+    zero). For directed graphs, this means no in-neighbors and no
+    out-neighbors.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+
+    n : node
+        A node in `G`.
+
+    Returns
+    -------
+    is_isolate : bool
+       True if and only if `n` has no neighbors.
+
+    Examples
+    --------
+    >>> G = nx.Graph()
+    >>> G.add_edge(1, 2)
+    >>> G.add_node(3)
+    >>> nx.is_isolate(G, 2)
+    False
+    >>> nx.is_isolate(G, 3)
+    True
+    """
+    return G.degree(n) == 0
+
+
+@nx._dispatchable
+def isolates(G):
+    """Iterator over isolates in the graph.
+
+    An *isolate* is a node with no neighbors (that is, with degree
+    zero). For directed graphs, this means no in-neighbors and no
+    out-neighbors.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+
+    Returns
+    -------
+    iterator
+        An iterator over the isolates of `G`.
+
+    Examples
+    --------
+    To get a list of all isolates of a graph, use the :class:`list`
+    constructor::
+
+        >>> G = nx.Graph()
+        >>> G.add_edge(1, 2)
+        >>> G.add_node(3)
+        >>> list(nx.isolates(G))
+        [3]
+
+    To remove all isolates in the graph, first create a list of the
+    isolates, then use :meth:`Graph.remove_nodes_from`::
+
+        >>> G.remove_nodes_from(list(nx.isolates(G)))
+        >>> list(G)
+        [1, 2]
+
+    For digraphs, isolates have zero in-degree and zero out_degre::
+
+        >>> G = nx.DiGraph([(0, 1), (1, 2)])
+        >>> G.add_node(3)
+        >>> list(nx.isolates(G))
+        [3]
+
+    """
+    return (n for n, d in G.degree() if d == 0)
+
+
+@nx._dispatchable
+def number_of_isolates(G):
+    """Returns the number of isolates in the graph.
+
+    An *isolate* is a node with no neighbors (that is, with degree
+    zero). For directed graphs, this means no in-neighbors and no
+    out-neighbors.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+
+    Returns
+    -------
+    int
+        The number of degree zero nodes in the graph `G`.
+
+    """
+    # TODO This can be parallelized.
+    return sum(1 for v in isolates(G))

venv/lib/python3.10/site-packages/networkx/algorithms/isomorphism/__init__.py

@@ -0,0 +1,7 @@
+from networkx.algorithms.isomorphism.isomorph import *
+from networkx.algorithms.isomorphism.vf2userfunc import *
+from networkx.algorithms.isomorphism.matchhelpers import *
+from networkx.algorithms.isomorphism.temporalisomorphvf2 import *
+from networkx.algorithms.isomorphism.ismags import *
+from networkx.algorithms.isomorphism.tree_isomorphism import *
+from networkx.algorithms.isomorphism.vf2pp import *

venv/lib/python3.10/site-packages/networkx/algorithms/isomorphism/ismags.py

@@ -0,0 +1,1163 @@
+"""
+ISMAGS Algorithm
+================
+
+Provides a Python implementation of the ISMAGS algorithm. [1]_
+
+It is capable of finding (subgraph) isomorphisms between two graphs, taking the
+symmetry of the subgraph into account. In most cases the VF2 algorithm is
+faster (at least on small graphs) than this implementation, but in some cases
+there is an exponential number of isomorphisms that are symmetrically
+equivalent. In that case, the ISMAGS algorithm will provide only one solution
+per symmetry group.
+
+>>> petersen = nx.petersen_graph()
+>>> ismags = nx.isomorphism.ISMAGS(petersen, petersen)
+>>> isomorphisms = list(ismags.isomorphisms_iter(symmetry=False))
+>>> len(isomorphisms)
+120
+>>> isomorphisms = list(ismags.isomorphisms_iter(symmetry=True))
+>>> answer = [{0: 0, 1: 1, 2: 2, 3: 3, 4: 4, 5: 5, 6: 6, 7: 7, 8: 8, 9: 9}]
+>>> answer == isomorphisms
+True
+
+In addition, this implementation also provides an interface to find the
+largest common induced subgraph [2]_ between any two graphs, again taking
+symmetry into account. Given `graph` and `subgraph` the algorithm will remove
+nodes from the `subgraph` until `subgraph` is isomorphic to a subgraph of
+`graph`. Since only the symmetry of `subgraph` is taken into account it is
+worth thinking about how you provide your graphs:
+
+>>> graph1 = nx.path_graph(4)
+>>> graph2 = nx.star_graph(3)
+>>> ismags = nx.isomorphism.ISMAGS(graph1, graph2)
+>>> ismags.is_isomorphic()
+False
+>>> largest_common_subgraph = list(ismags.largest_common_subgraph())
+>>> answer = [{1: 0, 0: 1, 2: 2}, {2: 0, 1: 1, 3: 2}]
+>>> answer == largest_common_subgraph
+True
+>>> ismags2 = nx.isomorphism.ISMAGS(graph2, graph1)
+>>> largest_common_subgraph = list(ismags2.largest_common_subgraph())
+>>> answer = [
+...     {1: 0, 0: 1, 2: 2},
+...     {1: 0, 0: 1, 3: 2},
+...     {2: 0, 0: 1, 1: 2},
+...     {2: 0, 0: 1, 3: 2},
+...     {3: 0, 0: 1, 1: 2},
+...     {3: 0, 0: 1, 2: 2},
+... ]
+>>> answer == largest_common_subgraph
+True
+
+However, when not taking symmetry into account, it doesn't matter:
+
+>>> largest_common_subgraph = list(ismags.largest_common_subgraph(symmetry=False))
+>>> answer = [
+...     {1: 0, 0: 1, 2: 2},
+...     {1: 0, 2: 1, 0: 2},
+...     {2: 0, 1: 1, 3: 2},
+...     {2: 0, 3: 1, 1: 2},
+...     {1: 0, 0: 1, 2: 3},
+...     {1: 0, 2: 1, 0: 3},
+...     {2: 0, 1: 1, 3: 3},
+...     {2: 0, 3: 1, 1: 3},
+...     {1: 0, 0: 2, 2: 3},
+...     {1: 0, 2: 2, 0: 3},
+...     {2: 0, 1: 2, 3: 3},
+...     {2: 0, 3: 2, 1: 3},
+... ]
+>>> answer == largest_common_subgraph
+True
+>>> largest_common_subgraph = list(ismags2.largest_common_subgraph(symmetry=False))
+>>> answer = [
+...     {1: 0, 0: 1, 2: 2},
+...     {1: 0, 0: 1, 3: 2},
+...     {2: 0, 0: 1, 1: 2},
+...     {2: 0, 0: 1, 3: 2},
+...     {3: 0, 0: 1, 1: 2},
+...     {3: 0, 0: 1, 2: 2},
+...     {1: 1, 0: 2, 2: 3},
+...     {1: 1, 0: 2, 3: 3},
+...     {2: 1, 0: 2, 1: 3},
+...     {2: 1, 0: 2, 3: 3},
+...     {3: 1, 0: 2, 1: 3},
+...     {3: 1, 0: 2, 2: 3},
+... ]
+>>> answer == largest_common_subgraph
+True
+
+Notes
+-----
+- The current implementation works for undirected graphs only. The algorithm
+  in general should work for directed graphs as well though.
+- Node keys for both provided graphs need to be fully orderable as well as
+  hashable.
+- Node and edge equality is assumed to be transitive: if A is equal to B, and
+  B is equal to C, then A is equal to C.
+
+References
+----------
+.. [1] M. Houbraken, S. Demeyer, T. Michoel, P. Audenaert, D. Colle,
+   M. Pickavet, "The Index-Based Subgraph Matching Algorithm with General
+   Symmetries (ISMAGS): Exploiting Symmetry for Faster Subgraph
+   Enumeration", PLoS One 9(5): e97896, 2014.
+   https://doi.org/10.1371/journal.pone.0097896
+.. [2] https://en.wikipedia.org/wiki/Maximum_common_induced_subgraph
+"""
+
+__all__ = ["ISMAGS"]
+
+import itertools
+from collections import Counter, defaultdict
+from functools import reduce, wraps
+
+
+def are_all_equal(iterable):
+    """
+    Returns ``True`` if and only if all elements in `iterable` are equal; and
+    ``False`` otherwise.
+
+    Parameters
+    ----------
+    iterable: collections.abc.Iterable
+        The container whose elements will be checked.
+
+    Returns
+    -------
+    bool
+        ``True`` iff all elements in `iterable` compare equal, ``False``
+        otherwise.
+    """
+    try:
+        shape = iterable.shape
+    except AttributeError:
+        pass
+    else:
+        if len(shape) > 1:
+            message = "The function does not works on multidimensional arrays."
+            raise NotImplementedError(message) from None
+
+    iterator = iter(iterable)
+    first = next(iterator, None)
+    return all(item == first for item in iterator)
+
+
+def make_partitions(items, test):
+    """
+    Partitions items into sets based on the outcome of ``test(item1, item2)``.
+    Pairs of items for which `test` returns `True` end up in the same set.
+
+    Parameters
+    ----------
+    items : collections.abc.Iterable[collections.abc.Hashable]
+        Items to partition
+    test : collections.abc.Callable[collections.abc.Hashable, collections.abc.Hashable]
+        A function that will be called with 2 arguments, taken from items.
+        Should return `True` if those 2 items need to end up in the same
+        partition, and `False` otherwise.
+
+    Returns
+    -------
+    list[set]
+        A list of sets, with each set containing part of the items in `items`,
+        such that ``all(test(*pair) for pair in  itertools.combinations(set, 2))
+        == True``
+
+    Notes
+    -----
+    The function `test` is assumed to be transitive: if ``test(a, b)`` and
+    ``test(b, c)`` return ``True``, then ``test(a, c)`` must also be ``True``.
+    """
+    partitions = []
+    for item in items:
+        for partition in partitions:
+            p_item = next(iter(partition))
+            if test(item, p_item):
+                partition.add(item)
+                break
+        else:  # No break
+            partitions.append({item})
+    return partitions
+
+
+def partition_to_color(partitions):
+    """
+    Creates a dictionary that maps each item in each partition to the index of
+    the partition to which it belongs.
+
+    Parameters
+    ----------
+    partitions: collections.abc.Sequence[collections.abc.Iterable]
+        As returned by :func:`make_partitions`.
+
+    Returns
+    -------
+    dict
+    """
+    colors = {}
+    for color, keys in enumerate(partitions):
+        for key in keys:
+            colors[key] = color
+    return colors
+
+
+def intersect(collection_of_sets):
+    """
+    Given an collection of sets, returns the intersection of those sets.
+
+    Parameters
+    ----------
+    collection_of_sets: collections.abc.Collection[set]
+        A collection of sets.
+
+    Returns
+    -------
+    set
+        An intersection of all sets in `collection_of_sets`. Will have the same
+        type as the item initially taken from `collection_of_sets`.
+    """
+    collection_of_sets = list(collection_of_sets)
+    first = collection_of_sets.pop()
+    out = reduce(set.intersection, collection_of_sets, set(first))
+    return type(first)(out)
+
+
+class ISMAGS:
+    """
+    Implements the ISMAGS subgraph matching algorithm. [1]_ ISMAGS stands for
+    "Index-based Subgraph Matching Algorithm with General Symmetries". As the
+    name implies, it is symmetry aware and will only generate non-symmetric
+    isomorphisms.
+
+    Notes
+    -----
+    The implementation imposes additional conditions compared to the VF2
+    algorithm on the graphs provided and the comparison functions
+    (:attr:`node_equality` and :attr:`edge_equality`):
+
+     - Node keys in both graphs must be orderable as well as hashable.
+     - Equality must be transitive: if A is equal to B, and B is equal to C,
+       then A must be equal to C.
+
+    Attributes
+    ----------
+    graph: networkx.Graph
+    subgraph: networkx.Graph
+    node_equality: collections.abc.Callable
+        The function called to see if two nodes should be considered equal.
+        It's signature looks like this:
+        ``f(graph1: networkx.Graph, node1, graph2: networkx.Graph, node2) -> bool``.
+        `node1` is a node in `graph1`, and `node2` a node in `graph2`.
+        Constructed from the argument `node_match`.
+    edge_equality: collections.abc.Callable
+        The function called to see if two edges should be considered equal.
+        It's signature looks like this:
+        ``f(graph1: networkx.Graph, edge1, graph2: networkx.Graph, edge2) -> bool``.
+        `edge1` is an edge in `graph1`, and `edge2` an edge in `graph2`.
+        Constructed from the argument `edge_match`.
+
+    References
+    ----------
+    .. [1] M. Houbraken, S. Demeyer, T. Michoel, P. Audenaert, D. Colle,
+       M. Pickavet, "The Index-Based Subgraph Matching Algorithm with General
+       Symmetries (ISMAGS): Exploiting Symmetry for Faster Subgraph
+       Enumeration", PLoS One 9(5): e97896, 2014.
+       https://doi.org/10.1371/journal.pone.0097896
+    """
+
+    def __init__(self, graph, subgraph, node_match=None, edge_match=None, cache=None):
+        """
+        Parameters
+        ----------
+        graph: networkx.Graph
+        subgraph: networkx.Graph
+        node_match: collections.abc.Callable or None
+            Function used to determine whether two nodes are equivalent. Its
+            signature should look like ``f(n1: dict, n2: dict) -> bool``, with
+            `n1` and `n2` node property dicts. See also
+            :func:`~networkx.algorithms.isomorphism.categorical_node_match` and
+            friends.
+            If `None`, all nodes are considered equal.
+        edge_match: collections.abc.Callable or None
+            Function used to determine whether two edges are equivalent. Its
+            signature should look like ``f(e1: dict, e2: dict) -> bool``, with
+            `e1` and `e2` edge property dicts. See also
+            :func:`~networkx.algorithms.isomorphism.categorical_edge_match` and
+            friends.
+            If `None`, all edges are considered equal.
+        cache: collections.abc.Mapping
+            A cache used for caching graph symmetries.
+        """
+        # TODO: graph and subgraph setter methods that invalidate the caches.
+        # TODO: allow for precomputed partitions and colors
+        self.graph = graph
+        self.subgraph = subgraph
+        self._symmetry_cache = cache
+        # Naming conventions are taken from the original paper. For your
+        # sanity:
+        #   sg: subgraph
+        #   g: graph
+        #   e: edge(s)
+        #   n: node(s)
+        # So: sgn means "subgraph nodes".
+        self._sgn_partitions_ = None
+        self._sge_partitions_ = None
+
+        self._sgn_colors_ = None
+        self._sge_colors_ = None
+
+        self._gn_partitions_ = None
+        self._ge_partitions_ = None
+
+        self._gn_colors_ = None
+        self._ge_colors_ = None
+
+        self._node_compat_ = None
+        self._edge_compat_ = None
+
+        if node_match is None:
+            self.node_equality = self._node_match_maker(lambda n1, n2: True)
+            self._sgn_partitions_ = [set(self.subgraph.nodes)]
+            self._gn_partitions_ = [set(self.graph.nodes)]
+            self._node_compat_ = {0: 0}
+        else:
+            self.node_equality = self._node_match_maker(node_match)
+        if edge_match is None:
+            self.edge_equality = self._edge_match_maker(lambda e1, e2: True)
+            self._sge_partitions_ = [set(self.subgraph.edges)]
+            self._ge_partitions_ = [set(self.graph.edges)]
+            self._edge_compat_ = {0: 0}
+        else:
+            self.edge_equality = self._edge_match_maker(edge_match)
+
+    @property
+    def _sgn_partitions(self):
+        if self._sgn_partitions_ is None:
+
+            def nodematch(node1, node2):
+                return self.node_equality(self.subgraph, node1, self.subgraph, node2)
+
+            self._sgn_partitions_ = make_partitions(self.subgraph.nodes, nodematch)
+        return self._sgn_partitions_
+
+    @property
+    def _sge_partitions(self):
+        if self._sge_partitions_ is None:
+
+            def edgematch(edge1, edge2):
+                return self.edge_equality(self.subgraph, edge1, self.subgraph, edge2)
+
+            self._sge_partitions_ = make_partitions(self.subgraph.edges, edgematch)
+        return self._sge_partitions_
+
+    @property
+    def _gn_partitions(self):
+        if self._gn_partitions_ is None:
+
+            def nodematch(node1, node2):
+                return self.node_equality(self.graph, node1, self.graph, node2)
+
+            self._gn_partitions_ = make_partitions(self.graph.nodes, nodematch)
+        return self._gn_partitions_
+
+    @property
+    def _ge_partitions(self):
+        if self._ge_partitions_ is None:
+
+            def edgematch(edge1, edge2):
+                return self.edge_equality(self.graph, edge1, self.graph, edge2)
+
+            self._ge_partitions_ = make_partitions(self.graph.edges, edgematch)
+        return self._ge_partitions_
+
+    @property
+    def _sgn_colors(self):
+        if self._sgn_colors_ is None:
+            self._sgn_colors_ = partition_to_color(self._sgn_partitions)
+        return self._sgn_colors_
+
+    @property
+    def _sge_colors(self):
+        if self._sge_colors_ is None:
+            self._sge_colors_ = partition_to_color(self._sge_partitions)
+        return self._sge_colors_
+
+    @property
+    def _gn_colors(self):
+        if self._gn_colors_ is None:
+            self._gn_colors_ = partition_to_color(self._gn_partitions)
+        return self._gn_colors_
+
+    @property
+    def _ge_colors(self):
+        if self._ge_colors_ is None:
+            self._ge_colors_ = partition_to_color(self._ge_partitions)
+        return self._ge_colors_
+
+    @property
+    def _node_compatibility(self):
+        if self._node_compat_ is not None:
+            return self._node_compat_
+        self._node_compat_ = {}
+        for sgn_part_color, gn_part_color in itertools.product(
+            range(len(self._sgn_partitions)), range(len(self._gn_partitions))
+        ):
+            sgn = next(iter(self._sgn_partitions[sgn_part_color]))
+            gn = next(iter(self._gn_partitions[gn_part_color]))
+            if self.node_equality(self.subgraph, sgn, self.graph, gn):
+                self._node_compat_[sgn_part_color] = gn_part_color
+        return self._node_compat_
+
+    @property
+    def _edge_compatibility(self):
+        if self._edge_compat_ is not None:
+            return self._edge_compat_
+        self._edge_compat_ = {}
+        for sge_part_color, ge_part_color in itertools.product(
+            range(len(self._sge_partitions)), range(len(self._ge_partitions))
+        ):
+            sge = next(iter(self._sge_partitions[sge_part_color]))
+            ge = next(iter(self._ge_partitions[ge_part_color]))
+            if self.edge_equality(self.subgraph, sge, self.graph, ge):
+                self._edge_compat_[sge_part_color] = ge_part_color
+        return self._edge_compat_
+
+    @staticmethod
+    def _node_match_maker(cmp):
+        @wraps(cmp)
+        def comparer(graph1, node1, graph2, node2):
+            return cmp(graph1.nodes[node1], graph2.nodes[node2])
+
+        return comparer
+
+    @staticmethod
+    def _edge_match_maker(cmp):
+        @wraps(cmp)
+        def comparer(graph1, edge1, graph2, edge2):
+            return cmp(graph1.edges[edge1], graph2.edges[edge2])
+
+        return comparer
+
+    def find_isomorphisms(self, symmetry=True):
+        """Find all subgraph isomorphisms between subgraph and graph
+
+        Finds isomorphisms where :attr:`subgraph` <= :attr:`graph`.
+
+        Parameters
+        ----------
+        symmetry: bool
+            Whether symmetry should be taken into account. If False, found
+            isomorphisms may be symmetrically equivalent.
+
+        Yields
+        ------
+        dict
+            The found isomorphism mappings of {graph_node: subgraph_node}.
+        """
+        # The networkx VF2 algorithm is slightly funny in when it yields an
+        # empty dict and when not.
+        if not self.subgraph:
+            yield {}
+            return
+        elif not self.graph:
+            return
+        elif len(self.graph) < len(self.subgraph):
+            return
+
+        if symmetry:
+            _, cosets = self.analyze_symmetry(
+                self.subgraph, self._sgn_partitions, self._sge_colors
+            )
+            constraints = self._make_constraints(cosets)
+        else:
+            constraints = []
+
+        candidates = self._find_nodecolor_candidates()
+        la_candidates = self._get_lookahead_candidates()
+        for sgn in self.subgraph:
+            extra_candidates = la_candidates[sgn]
+            if extra_candidates:
+                candidates[sgn] = candidates[sgn] | {frozenset(extra_candidates)}
+
+        if any(candidates.values()):
+            start_sgn = min(candidates, key=lambda n: min(candidates[n], key=len))
+            candidates[start_sgn] = (intersect(candidates[start_sgn]),)
+            yield from self._map_nodes(start_sgn, candidates, constraints)
+        else:
+            return
+
+    @staticmethod
+    def _find_neighbor_color_count(graph, node, node_color, edge_color):
+        """
+        For `node` in `graph`, count the number of edges of a specific color
+        it has to nodes of a specific color.
+        """
+        counts = Counter()
+        neighbors = graph[node]
+        for neighbor in neighbors:
+            n_color = node_color[neighbor]
+            if (node, neighbor) in edge_color:
+                e_color = edge_color[node, neighbor]
+            else:
+                e_color = edge_color[neighbor, node]
+            counts[e_color, n_color] += 1
+        return counts
+
+    def _get_lookahead_candidates(self):
+        """
+        Returns a mapping of {subgraph node: collection of graph nodes} for
+        which the graph nodes are feasible candidates for the subgraph node, as
+        determined by looking ahead one edge.
+        """
+        g_counts = {}
+        for gn in self.graph:
+            g_counts[gn] = self._find_neighbor_color_count(
+                self.graph, gn, self._gn_colors, self._ge_colors
+            )
+        candidates = defaultdict(set)
+        for sgn in self.subgraph:
+            sg_count = self._find_neighbor_color_count(
+                self.subgraph, sgn, self._sgn_colors, self._sge_colors
+            )
+            new_sg_count = Counter()
+            for (sge_color, sgn_color), count in sg_count.items():
+                try:
+                    ge_color = self._edge_compatibility[sge_color]
+                    gn_color = self._node_compatibility[sgn_color]
+                except KeyError:
+                    pass
+                else:
+                    new_sg_count[ge_color, gn_color] = count
+
+            for gn, g_count in g_counts.items():
+                if all(new_sg_count[x] <= g_count[x] for x in new_sg_count):
+                    # Valid candidate
+                    candidates[sgn].add(gn)
+        return candidates
+
+    def largest_common_subgraph(self, symmetry=True):
+        """
+        Find the largest common induced subgraphs between :attr:`subgraph` and
+        :attr:`graph`.
+
+        Parameters
+        ----------
+        symmetry: bool
+            Whether symmetry should be taken into account. If False, found
+            largest common subgraphs may be symmetrically equivalent.
+
+        Yields
+        ------
+        dict
+            The found isomorphism mappings of {graph_node: subgraph_node}.
+        """
+        # The networkx VF2 algorithm is slightly funny in when it yields an
+        # empty dict and when not.
+        if not self.subgraph:
+            yield {}
+            return
+        elif not self.graph:
+            return
+
+        if symmetry:
+            _, cosets = self.analyze_symmetry(
+                self.subgraph, self._sgn_partitions, self._sge_colors
+            )
+            constraints = self._make_constraints(cosets)
+        else:
+            constraints = []
+
+        candidates = self._find_nodecolor_candidates()
+
+        if any(candidates.values()):
+            yield from self._largest_common_subgraph(candidates, constraints)
+        else:
+            return
+
+    def analyze_symmetry(self, graph, node_partitions, edge_colors):
+        """
+        Find a minimal set of permutations and corresponding co-sets that
+        describe the symmetry of `graph`, given the node and edge equalities
+        given by `node_partitions` and `edge_colors`, respectively.
+
+        Parameters
+        ----------
+        graph : networkx.Graph
+            The graph whose symmetry should be analyzed.
+        node_partitions : list of sets
+            A list of sets containing node keys. Node keys in the same set
+            are considered equivalent. Every node key in `graph` should be in
+            exactly one of the sets. If all nodes are equivalent, this should
+            be ``[set(graph.nodes)]``.
+        edge_colors : dict mapping edges to their colors
+            A dict mapping every edge in `graph` to its corresponding color.
+            Edges with the same color are considered equivalent. If all edges
+            are equivalent, this should be ``{e: 0 for e in graph.edges}``.
+
+
+        Returns
+        -------
+        set[frozenset]
+            The found permutations. This is a set of frozensets of pairs of node
+            keys which can be exchanged without changing :attr:`subgraph`.
+        dict[collections.abc.Hashable, set[collections.abc.Hashable]]
+            The found co-sets. The co-sets is a dictionary of
+            ``{node key: set of node keys}``.
+            Every key-value pair describes which ``values`` can be interchanged
+            without changing nodes less than ``key``.
+        """
+        if self._symmetry_cache is not None:
+            key = hash(
+                (
+                    tuple(graph.nodes),
+                    tuple(graph.edges),
+                    tuple(map(tuple, node_partitions)),
+                    tuple(edge_colors.items()),
+                )
+            )
+            if key in self._symmetry_cache:
+                return self._symmetry_cache[key]
+        node_partitions = list(
+            self._refine_node_partitions(graph, node_partitions, edge_colors)
+        )
+        assert len(node_partitions) == 1
+        node_partitions = node_partitions[0]
+        permutations, cosets = self._process_ordered_pair_partitions(
+            graph, node_partitions, node_partitions, edge_colors
+        )
+        if self._symmetry_cache is not None:
+            self._symmetry_cache[key] = permutations, cosets
+        return permutations, cosets
+
+    def is_isomorphic(self, symmetry=False):
+        """
+        Returns True if :attr:`graph` is isomorphic to :attr:`subgraph` and
+        False otherwise.
+
+        Returns
+        -------
+        bool
+        """
+        return len(self.subgraph) == len(self.graph) and self.subgraph_is_isomorphic(
+            symmetry
+        )
+
+    def subgraph_is_isomorphic(self, symmetry=False):
+        """
+        Returns True if a subgraph of :attr:`graph` is isomorphic to
+        :attr:`subgraph` and False otherwise.
+
+        Returns
+        -------
+        bool
+        """
+        # symmetry=False, since we only need to know whether there is any
+        # example; figuring out all symmetry elements probably costs more time
+        # than it gains.
+        isom = next(self.subgraph_isomorphisms_iter(symmetry=symmetry), None)
+        return isom is not None
+
+    def isomorphisms_iter(self, symmetry=True):
+        """
+        Does the same as :meth:`find_isomorphisms` if :attr:`graph` and
+        :attr:`subgraph` have the same number of nodes.
+        """
+        if len(self.graph) == len(self.subgraph):
+            yield from self.subgraph_isomorphisms_iter(symmetry=symmetry)
+
+    def subgraph_isomorphisms_iter(self, symmetry=True):
+        """Alternative name for :meth:`find_isomorphisms`."""
+        return self.find_isomorphisms(symmetry)
+
+    def _find_nodecolor_candidates(self):
+        """
+        Per node in subgraph find all nodes in graph that have the same color.
+        """
+        candidates = defaultdict(set)
+        for sgn in self.subgraph.nodes:
+            sgn_color = self._sgn_colors[sgn]
+            if sgn_color in self._node_compatibility:
+                gn_color = self._node_compatibility[sgn_color]
+                candidates[sgn].add(frozenset(self._gn_partitions[gn_color]))
+            else:
+                candidates[sgn].add(frozenset())
+        candidates = dict(candidates)
+        for sgn, options in candidates.items():
+            candidates[sgn] = frozenset(options)
+        return candidates
+
+    @staticmethod
+    def _make_constraints(cosets):
+        """
+        Turn cosets into constraints.
+        """
+        constraints = []
+        for node_i, node_ts in cosets.items():
+            for node_t in node_ts:
+                if node_i != node_t:
+                    # Node i must be smaller than node t.
+                    constraints.append((node_i, node_t))
+        return constraints
+
+    @staticmethod
+    def _find_node_edge_color(graph, node_colors, edge_colors):
+        """
+        For every node in graph, come up with a color that combines 1) the
+        color of the node, and 2) the number of edges of a color to each type
+        of node.
+        """
+        counts = defaultdict(lambda: defaultdict(int))
+        for node1, node2 in graph.edges:
+            if (node1, node2) in edge_colors:
+                # FIXME directed graphs
+                ecolor = edge_colors[node1, node2]
+            else:
+                ecolor = edge_colors[node2, node1]
+            # Count per node how many edges it has of what color to nodes of
+            # what color
+            counts[node1][ecolor, node_colors[node2]] += 1
+            counts[node2][ecolor, node_colors[node1]] += 1
+
+        node_edge_colors = {}
+        for node in graph.nodes:
+            node_edge_colors[node] = node_colors[node], set(counts[node].items())
+
+        return node_edge_colors
+
+    @staticmethod
+    def _get_permutations_by_length(items):
+        """
+        Get all permutations of items, but only permute items with the same
+        length.
+
+        >>> found = list(ISMAGS._get_permutations_by_length([[1], [2], [3, 4], [4, 5]]))
+        >>> answer = [
+        ...     (([1], [2]), ([3, 4], [4, 5])),
+        ...     (([1], [2]), ([4, 5], [3, 4])),
+        ...     (([2], [1]), ([3, 4], [4, 5])),
+        ...     (([2], [1]), ([4, 5], [3, 4])),
+        ... ]
+        >>> found == answer
+        True
+        """
+        by_len = defaultdict(list)
+        for item in items:
+            by_len[len(item)].append(item)
+
+        yield from itertools.product(
+            *(itertools.permutations(by_len[l]) for l in sorted(by_len))
+        )
+
+    @classmethod
+    def _refine_node_partitions(cls, graph, node_partitions, edge_colors, branch=False):
+        """
+        Given a partition of nodes in graph, make the partitions smaller such
+        that all nodes in a partition have 1) the same color, and 2) the same
+        number of edges to specific other partitions.
+        """
+
+        def equal_color(node1, node2):
+            return node_edge_colors[node1] == node_edge_colors[node2]
+
+        node_partitions = list(node_partitions)
+        node_colors = partition_to_color(node_partitions)
+        node_edge_colors = cls._find_node_edge_color(graph, node_colors, edge_colors)
+        if all(
+            are_all_equal(node_edge_colors[node] for node in partition)
+            for partition in node_partitions
+        ):
+            yield node_partitions
+            return
+
+        new_partitions = []
+        output = [new_partitions]
+        for partition in node_partitions:
+            if not are_all_equal(node_edge_colors[node] for node in partition):
+                refined = make_partitions(partition, equal_color)
+                if (
+                    branch
+                    and len(refined) != 1
+                    and len({len(r) for r in refined}) != len([len(r) for r in refined])
+                ):
+                    # This is where it breaks. There are multiple new cells
+                    # in refined with the same length, and their order
+                    # matters.
+                    # So option 1) Hit it with a big hammer and simply make all
+                    # orderings.
+                    permutations = cls._get_permutations_by_length(refined)
+                    new_output = []
+                    for n_p in output:
+                        for permutation in permutations:
+                            new_output.append(n_p + list(permutation[0]))
+                    output = new_output
+                else:
+                    for n_p in output:
+                        n_p.extend(sorted(refined, key=len))
+            else:
+                for n_p in output:
+                    n_p.append(partition)
+        for n_p in output:
+            yield from cls._refine_node_partitions(graph, n_p, edge_colors, branch)
+
+    def _edges_of_same_color(self, sgn1, sgn2):
+        """
+        Returns all edges in :attr:`graph` that have the same colour as the
+        edge between sgn1 and sgn2 in :attr:`subgraph`.
+        """
+        if (sgn1, sgn2) in self._sge_colors:
+            # FIXME directed graphs
+            sge_color = self._sge_colors[sgn1, sgn2]
+        else:
+            sge_color = self._sge_colors[sgn2, sgn1]
+        if sge_color in self._edge_compatibility:
+            ge_color = self._edge_compatibility[sge_color]
+            g_edges = self._ge_partitions[ge_color]
+        else:
+            g_edges = []
+        return g_edges
+
+    def _map_nodes(self, sgn, candidates, constraints, mapping=None, to_be_mapped=None):
+        """
+        Find all subgraph isomorphisms honoring constraints.
+        """
+        if mapping is None:
+            mapping = {}
+        else:
+            mapping = mapping.copy()
+        if to_be_mapped is None:
+            to_be_mapped = set(self.subgraph.nodes)
+
+        # Note, we modify candidates here. Doesn't seem to affect results, but
+        # remember this.
+        # candidates = candidates.copy()
+        sgn_candidates = intersect(candidates[sgn])
+        candidates[sgn] = frozenset([sgn_candidates])
+        for gn in sgn_candidates:
+            # We're going to try to map sgn to gn.
+            if gn in mapping.values() or sgn not in to_be_mapped:
+                # gn is already mapped to something
+                continue  # pragma: no cover
+
+            # REDUCTION and COMBINATION
+            mapping[sgn] = gn
+            # BASECASE
+            if to_be_mapped == set(mapping.keys()):
+                yield {v: k for k, v in mapping.items()}
+                continue
+            left_to_map = to_be_mapped - set(mapping.keys())
+
+            new_candidates = candidates.copy()
+            sgn_nbrs = set(self.subgraph[sgn])
+            not_gn_nbrs = set(self.graph.nodes) - set(self.graph[gn])
+            for sgn2 in left_to_map:
+                if sgn2 not in sgn_nbrs:
+                    gn2_options = not_gn_nbrs
+                else:
+                    # Get all edges to gn of the right color:
+                    g_edges = self._edges_of_same_color(sgn, sgn2)
+                    # FIXME directed graphs
+                    # And all nodes involved in those which are connected to gn
+                    gn2_options = {n for e in g_edges for n in e if gn in e}
+                # Node color compatibility should be taken care of by the
+                # initial candidate lists made by find_subgraphs
+
+                # Add gn2_options to the right collection. Since new_candidates
+                # is a dict of frozensets of frozensets of node indices it's
+                # a bit clunky. We can't do .add, and + also doesn't work. We
+                # could do |, but I deem union to be clearer.
+                new_candidates[sgn2] = new_candidates[sgn2].union(
+                    [frozenset(gn2_options)]
+                )
+
+                if (sgn, sgn2) in constraints:
+                    gn2_options = {gn2 for gn2 in self.graph if gn2 > gn}
+                elif (sgn2, sgn) in constraints:
+                    gn2_options = {gn2 for gn2 in self.graph if gn2 < gn}
+                else:
+                    continue  # pragma: no cover
+                new_candidates[sgn2] = new_candidates[sgn2].union(
+                    [frozenset(gn2_options)]
+                )
+
+            # The next node is the one that is unmapped and has fewest
+            # candidates
+            next_sgn = min(left_to_map, key=lambda n: min(new_candidates[n], key=len))
+            yield from self._map_nodes(
+                next_sgn,
+                new_candidates,
+                constraints,
+                mapping=mapping,
+                to_be_mapped=to_be_mapped,
+            )
+            # Unmap sgn-gn. Strictly not necessary since it'd get overwritten
+            # when making a new mapping for sgn.
+            # del mapping[sgn]
+
+    def _largest_common_subgraph(self, candidates, constraints, to_be_mapped=None):
+        """
+        Find all largest common subgraphs honoring constraints.
+        """
+        if to_be_mapped is None:
+            to_be_mapped = {frozenset(self.subgraph.nodes)}
+
+        # The LCS problem is basically a repeated subgraph isomorphism problem
+        # with smaller and smaller subgraphs. We store the nodes that are
+        # "part of" the subgraph in to_be_mapped, and we make it a little
+        # smaller every iteration.
+
+        current_size = len(next(iter(to_be_mapped), []))
+
+        found_iso = False
+        if current_size <= len(self.graph):
+            # There's no point in trying to find isomorphisms of
+            # graph >= subgraph if subgraph has more nodes than graph.
+
+            # Try the isomorphism first with the nodes with lowest ID. So sort
+            # them. Those are more likely to be part of the final
+            # correspondence. This makes finding the first answer(s) faster. In
+            # theory.
+            for nodes in sorted(to_be_mapped, key=sorted):
+                # Find the isomorphism between subgraph[to_be_mapped] <= graph
+                next_sgn = min(nodes, key=lambda n: min(candidates[n], key=len))
+                isomorphs = self._map_nodes(
+                    next_sgn, candidates, constraints, to_be_mapped=nodes
+                )
+
+                # This is effectively `yield from isomorphs`, except that we look
+                # whether an item was yielded.
+                try:
+                    item = next(isomorphs)
+                except StopIteration:
+                    pass
+                else:
+                    yield item
+                    yield from isomorphs
+                    found_iso = True
+
+        # BASECASE
+        if found_iso or current_size == 1:
+            # Shrinking has no point because either 1) we end up with a smaller
+            # common subgraph (and we want the largest), or 2) there'll be no
+            # more subgraph.
+            return
+
+        left_to_be_mapped = set()
+        for nodes in to_be_mapped:
+            for sgn in nodes:
+                # We're going to remove sgn from to_be_mapped, but subject to
+                # symmetry constraints. We know that for every constraint we
+                # have those subgraph nodes are equal. So whenever we would
+                # remove the lower part of a constraint, remove the higher
+                # instead. This is all dealth with by _remove_node. And because
+                # left_to_be_mapped is a set, we don't do double work.
+
+                # And finally, make the subgraph one node smaller.
+                # REDUCTION
+                new_nodes = self._remove_node(sgn, nodes, constraints)
+                left_to_be_mapped.add(new_nodes)
+        # COMBINATION
+        yield from self._largest_common_subgraph(
+            candidates, constraints, to_be_mapped=left_to_be_mapped
+        )
+
+    @staticmethod
+    def _remove_node(node, nodes, constraints):
+        """
+        Returns a new set where node has been removed from nodes, subject to
+        symmetry constraints. We know, that for every constraint we have
+        those subgraph nodes are equal. So whenever we would remove the
+        lower part of a constraint, remove the higher instead.
+        """
+        while True:
+            for low, high in constraints:
+                if low == node and high in nodes:
+                    node = high
+                    break
+            else:  # no break, couldn't find node in constraints
+                break
+        return frozenset(nodes - {node})
+
+    @staticmethod
+    def _find_permutations(top_partitions, bottom_partitions):
+        """
+        Return the pairs of top/bottom partitions where the partitions are
+        different. Ensures that all partitions in both top and bottom
+        partitions have size 1.
+        """
+        # Find permutations
+        permutations = set()
+        for top, bot in zip(top_partitions, bottom_partitions):
+            # top and bot have only one element
+            if len(top) != 1 or len(bot) != 1:
+                raise IndexError(
+                    "Not all nodes are coupled. This is"
+                    f" impossible: {top_partitions}, {bottom_partitions}"
+                )
+            if top != bot:
+                permutations.add(frozenset((next(iter(top)), next(iter(bot)))))
+        return permutations
+
+    @staticmethod
+    def _update_orbits(orbits, permutations):
+        """
+        Update orbits based on permutations. Orbits is modified in place.
+        For every pair of items in permutations their respective orbits are
+        merged.
+        """
+        for permutation in permutations:
+            node, node2 = permutation
+            # Find the orbits that contain node and node2, and replace the
+            # orbit containing node with the union
+            first = second = None
+            for idx, orbit in enumerate(orbits):
+                if first is not None and second is not None:
+                    break
+                if node in orbit:
+                    first = idx
+                if node2 in orbit:
+                    second = idx
+            if first != second:
+                orbits[first].update(orbits[second])
+                del orbits[second]
+
+    def _couple_nodes(
+        self,
+        top_partitions,
+        bottom_partitions,
+        pair_idx,
+        t_node,
+        b_node,
+        graph,
+        edge_colors,
+    ):
+        """
+        Generate new partitions from top and bottom_partitions where t_node is
+        coupled to b_node. pair_idx is the index of the partitions where t_ and
+        b_node can be found.
+        """
+        t_partition = top_partitions[pair_idx]
+        b_partition = bottom_partitions[pair_idx]
+        assert t_node in t_partition and b_node in b_partition
+        # Couple node to node2. This means they get their own partition
+        new_top_partitions = [top.copy() for top in top_partitions]
+        new_bottom_partitions = [bot.copy() for bot in bottom_partitions]
+        new_t_groups = {t_node}, t_partition - {t_node}
+        new_b_groups = {b_node}, b_partition - {b_node}
+        # Replace the old partitions with the coupled ones
+        del new_top_partitions[pair_idx]
+        del new_bottom_partitions[pair_idx]
+        new_top_partitions[pair_idx:pair_idx] = new_t_groups
+        new_bottom_partitions[pair_idx:pair_idx] = new_b_groups
+
+        new_top_partitions = self._refine_node_partitions(
+            graph, new_top_partitions, edge_colors
+        )
+        new_bottom_partitions = self._refine_node_partitions(
+            graph, new_bottom_partitions, edge_colors, branch=True
+        )
+        new_top_partitions = list(new_top_partitions)
+        assert len(new_top_partitions) == 1
+        new_top_partitions = new_top_partitions[0]
+        for bot in new_bottom_partitions:
+            yield list(new_top_partitions), bot
+
+    def _process_ordered_pair_partitions(
+        self,
+        graph,
+        top_partitions,
+        bottom_partitions,
+        edge_colors,
+        orbits=None,
+        cosets=None,
+    ):
+        """
+        Processes ordered pair partitions as per the reference paper. Finds and
+        returns all permutations and cosets that leave the graph unchanged.
+        """
+        if orbits is None:
+            orbits = [{node} for node in graph.nodes]
+        else:
+            # Note that we don't copy orbits when we are given one. This means
+            # we leak information between the recursive branches. This is
+            # intentional!
+            orbits = orbits
+        if cosets is None:
+            cosets = {}
+        else:
+            cosets = cosets.copy()
+
+        assert all(
+            len(t_p) == len(b_p) for t_p, b_p in zip(top_partitions, bottom_partitions)
+        )
+
+        # BASECASE
+        if all(len(top) == 1 for top in top_partitions):
+            # All nodes are mapped
+            permutations = self._find_permutations(top_partitions, bottom_partitions)
+            self._update_orbits(orbits, permutations)
+            if permutations:
+                return [permutations], cosets
+            else:
+                return [], cosets
+
+        permutations = []
+        unmapped_nodes = {
+            (node, idx)
+            for idx, t_partition in enumerate(top_partitions)
+            for node in t_partition
+            if len(t_partition) > 1
+        }
+        node, pair_idx = min(unmapped_nodes)
+        b_partition = bottom_partitions[pair_idx]
+
+        for node2 in sorted(b_partition):
+            if len(b_partition) == 1:
+                # Can never result in symmetry
+                continue
+            if node != node2 and any(
+                node in orbit and node2 in orbit for orbit in orbits
+            ):
+                # Orbit prune branch
+                continue
+            # REDUCTION
+            # Couple node to node2
+            partitions = self._couple_nodes(
+                top_partitions,
+                bottom_partitions,
+                pair_idx,
+                node,
+                node2,
+                graph,
+                edge_colors,
+            )
+            for opp in partitions:
+                new_top_partitions, new_bottom_partitions = opp
+
+                new_perms, new_cosets = self._process_ordered_pair_partitions(
+                    graph,
+                    new_top_partitions,
+                    new_bottom_partitions,
+                    edge_colors,
+                    orbits,
+                    cosets,
+                )
+                # COMBINATION
+                permutations += new_perms
+                cosets.update(new_cosets)
+
+        mapped = {
+            k
+            for top, bottom in zip(top_partitions, bottom_partitions)
+            for k in top
+            if len(top) == 1 and top == bottom
+        }
+        ks = {k for k in graph.nodes if k < node}
+        # Have all nodes with ID < node been mapped?
+        find_coset = ks <= mapped and node not in cosets
+        if find_coset:
+            # Find the orbit that contains node
+            for orbit in orbits:
+                if node in orbit:
+                    cosets[node] = orbit.copy()
+        return permutations, cosets

venv/lib/python3.10/site-packages/networkx/algorithms/isomorphism/isomorph.py

@@ -0,0 +1,248 @@
+"""
+Graph isomorphism functions.
+"""
+import networkx as nx
+from networkx.exception import NetworkXError
+
+__all__ = [
+    "could_be_isomorphic",
+    "fast_could_be_isomorphic",
+    "faster_could_be_isomorphic",
+    "is_isomorphic",
+]
+
+
+@nx._dispatchable(graphs={"G1": 0, "G2": 1})
+def could_be_isomorphic(G1, G2):
+    """Returns False if graphs are definitely not isomorphic.
+    True does NOT guarantee isomorphism.
+
+    Parameters
+    ----------
+    G1, G2 : graphs
+       The two graphs G1 and G2 must be the same type.
+
+    Notes
+    -----
+    Checks for matching degree, triangle, and number of cliques sequences.
+    The triangle sequence contains the number of triangles each node is part of.
+    The clique sequence contains for each node the number of maximal cliques
+    involving that node.
+
+    """
+
+    # Check global properties
+    if G1.order() != G2.order():
+        return False
+
+    # Check local properties
+    d1 = G1.degree()
+    t1 = nx.triangles(G1)
+    clqs_1 = list(nx.find_cliques(G1))
+    c1 = {n: sum(1 for c in clqs_1 if n in c) for n in G1}  # number of cliques
+    props1 = [[d, t1[v], c1[v]] for v, d in d1]
+    props1.sort()
+
+    d2 = G2.degree()
+    t2 = nx.triangles(G2)
+    clqs_2 = list(nx.find_cliques(G2))
+    c2 = {n: sum(1 for c in clqs_2 if n in c) for n in G2}  # number of cliques
+    props2 = [[d, t2[v], c2[v]] for v, d in d2]
+    props2.sort()
+
+    if props1 != props2:
+        return False
+
+    # OK...
+    return True
+
+
+graph_could_be_isomorphic = could_be_isomorphic
+
+
+@nx._dispatchable(graphs={"G1": 0, "G2": 1})
+def fast_could_be_isomorphic(G1, G2):
+    """Returns False if graphs are definitely not isomorphic.
+
+    True does NOT guarantee isomorphism.
+
+    Parameters
+    ----------
+    G1, G2 : graphs
+       The two graphs G1 and G2 must be the same type.
+
+    Notes
+    -----
+    Checks for matching degree and triangle sequences. The triangle
+    sequence contains the number of triangles each node is part of.
+    """
+    # Check global properties
+    if G1.order() != G2.order():
+        return False
+
+    # Check local properties
+    d1 = G1.degree()
+    t1 = nx.triangles(G1)
+    props1 = [[d, t1[v]] for v, d in d1]
+    props1.sort()
+
+    d2 = G2.degree()
+    t2 = nx.triangles(G2)
+    props2 = [[d, t2[v]] for v, d in d2]
+    props2.sort()
+
+    if props1 != props2:
+        return False
+
+    # OK...
+    return True
+
+
+fast_graph_could_be_isomorphic = fast_could_be_isomorphic
+
+
+@nx._dispatchable(graphs={"G1": 0, "G2": 1})
+def faster_could_be_isomorphic(G1, G2):
+    """Returns False if graphs are definitely not isomorphic.
+
+    True does NOT guarantee isomorphism.
+
+    Parameters
+    ----------
+    G1, G2 : graphs
+       The two graphs G1 and G2 must be the same type.
+
+    Notes
+    -----
+    Checks for matching degree sequences.
+    """
+    # Check global properties
+    if G1.order() != G2.order():
+        return False
+
+    # Check local properties
+    d1 = sorted(d for n, d in G1.degree())
+    d2 = sorted(d for n, d in G2.degree())
+
+    if d1 != d2:
+        return False
+
+    # OK...
+    return True
+
+
+faster_graph_could_be_isomorphic = faster_could_be_isomorphic
+
+
+@nx._dispatchable(
+    graphs={"G1": 0, "G2": 1},
+    preserve_edge_attrs="edge_match",
+    preserve_node_attrs="node_match",
+)
+def is_isomorphic(G1, G2, node_match=None, edge_match=None):
+    """Returns True if the graphs G1 and G2 are isomorphic and False otherwise.
+
+    Parameters
+    ----------
+    G1, G2: graphs
+        The two graphs G1 and G2 must be the same type.
+
+    node_match : callable
+        A function that returns True if node n1 in G1 and n2 in G2 should
+        be considered equal during the isomorphism test.
+        If node_match is not specified then node attributes are not considered.
+
+        The function will be called like
+
+           node_match(G1.nodes[n1], G2.nodes[n2]).
+
+        That is, the function will receive the node attribute dictionaries
+        for n1 and n2 as inputs.
+
+    edge_match : callable
+        A function that returns True if the edge attribute dictionary
+        for the pair of nodes (u1, v1) in G1 and (u2, v2) in G2 should
+        be considered equal during the isomorphism test.  If edge_match is
+        not specified then edge attributes are not considered.
+
+        The function will be called like
+
+           edge_match(G1[u1][v1], G2[u2][v2]).
+
+        That is, the function will receive the edge attribute dictionaries
+        of the edges under consideration.
+
+    Notes
+    -----
+    Uses the vf2 algorithm [1]_.
+
+    Examples
+    --------
+    >>> import networkx.algorithms.isomorphism as iso
+
+    For digraphs G1 and G2, using 'weight' edge attribute (default: 1)
+
+    >>> G1 = nx.DiGraph()
+    >>> G2 = nx.DiGraph()
+    >>> nx.add_path(G1, [1, 2, 3, 4], weight=1)
+    >>> nx.add_path(G2, [10, 20, 30, 40], weight=2)
+    >>> em = iso.numerical_edge_match("weight", 1)
+    >>> nx.is_isomorphic(G1, G2)  # no weights considered
+    True
+    >>> nx.is_isomorphic(G1, G2, edge_match=em)  # match weights
+    False
+
+    For multidigraphs G1 and G2, using 'fill' node attribute (default: '')
+
+    >>> G1 = nx.MultiDiGraph()
+    >>> G2 = nx.MultiDiGraph()
+    >>> G1.add_nodes_from([1, 2, 3], fill="red")
+    >>> G2.add_nodes_from([10, 20, 30, 40], fill="red")
+    >>> nx.add_path(G1, [1, 2, 3, 4], weight=3, linewidth=2.5)
+    >>> nx.add_path(G2, [10, 20, 30, 40], weight=3)
+    >>> nm = iso.categorical_node_match("fill", "red")
+    >>> nx.is_isomorphic(G1, G2, node_match=nm)
+    True
+
+    For multidigraphs G1 and G2, using 'weight' edge attribute (default: 7)
+
+    >>> G1.add_edge(1, 2, weight=7)
+    1
+    >>> G2.add_edge(10, 20)
+    1
+    >>> em = iso.numerical_multiedge_match("weight", 7, rtol=1e-6)
+    >>> nx.is_isomorphic(G1, G2, edge_match=em)
+    True
+
+    For multigraphs G1 and G2, using 'weight' and 'linewidth' edge attributes
+    with default values 7 and 2.5. Also using 'fill' node attribute with
+    default value 'red'.
+
+    >>> em = iso.numerical_multiedge_match(["weight", "linewidth"], [7, 2.5])
+    >>> nm = iso.categorical_node_match("fill", "red")
+    >>> nx.is_isomorphic(G1, G2, edge_match=em, node_match=nm)
+    True
+
+    See Also
+    --------
+    numerical_node_match, numerical_edge_match, numerical_multiedge_match
+    categorical_node_match, categorical_edge_match, categorical_multiedge_match
+
+    References
+    ----------
+    .. [1]  L. P. Cordella, P. Foggia, C. Sansone, M. Vento,
+       "An Improved Algorithm for Matching Large Graphs",
+       3rd IAPR-TC15 Workshop  on Graph-based Representations in
+       Pattern Recognition, Cuen, pp. 149-159, 2001.
+       https://www.researchgate.net/publication/200034365_An_Improved_Algorithm_for_Matching_Large_Graphs
+    """
+    if G1.is_directed() and G2.is_directed():
+        GM = nx.algorithms.isomorphism.DiGraphMatcher
+    elif (not G1.is_directed()) and (not G2.is_directed()):
+        GM = nx.algorithms.isomorphism.GraphMatcher
+    else:
+        raise NetworkXError("Graphs G1 and G2 are not of the same type.")
+
+    gm = GM(G1, G2, node_match=node_match, edge_match=edge_match)
+
+    return gm.is_isomorphic()

venv/lib/python3.10/site-packages/networkx/algorithms/isomorphism/isomorphvf2.py

@@ -0,0 +1,1065 @@
+"""
+*************
+VF2 Algorithm
+*************
+
+An implementation of VF2 algorithm for graph isomorphism testing.
+
+The simplest interface to use this module is to call the
+:func:`is_isomorphic <networkx.algorithms.isomorphism.is_isomorphic>`
+function.
+
+Introduction
+------------
+
+The GraphMatcher and DiGraphMatcher are responsible for matching
+graphs or directed graphs in a predetermined manner.  This
+usually means a check for an isomorphism, though other checks
+are also possible.  For example, a subgraph of one graph
+can be checked for isomorphism to a second graph.
+
+Matching is done via syntactic feasibility. It is also possible
+to check for semantic feasibility. Feasibility, then, is defined
+as the logical AND of the two functions.
+
+To include a semantic check, the (Di)GraphMatcher class should be
+subclassed, and the
+:meth:`semantic_feasibility <networkx.algorithms.isomorphism.GraphMatcher.semantic_feasibility>`
+function should be redefined.  By default, the semantic feasibility function always
+returns ``True``.  The effect of this is that semantics are not
+considered in the matching of G1 and G2.
+
+Examples
+--------
+
+Suppose G1 and G2 are isomorphic graphs. Verification is as follows:
+
+>>> from networkx.algorithms import isomorphism
+>>> G1 = nx.path_graph(4)
+>>> G2 = nx.path_graph(4)
+>>> GM = isomorphism.GraphMatcher(G1, G2)
+>>> GM.is_isomorphic()
+True
+
+GM.mapping stores the isomorphism mapping from G1 to G2.
+
+>>> GM.mapping
+{0: 0, 1: 1, 2: 2, 3: 3}
+
+
+Suppose G1 and G2 are isomorphic directed graphs.
+Verification is as follows:
+
+>>> G1 = nx.path_graph(4, create_using=nx.DiGraph())
+>>> G2 = nx.path_graph(4, create_using=nx.DiGraph())
+>>> DiGM = isomorphism.DiGraphMatcher(G1, G2)
+>>> DiGM.is_isomorphic()
+True
+
+DiGM.mapping stores the isomorphism mapping from G1 to G2.
+
+>>> DiGM.mapping
+{0: 0, 1: 1, 2: 2, 3: 3}
+
+
+
+Subgraph Isomorphism
+--------------------
+Graph theory literature can be ambiguous about the meaning of the
+above statement, and we seek to clarify it now.
+
+In the VF2 literature, a mapping `M` is said to be a graph-subgraph
+isomorphism iff `M` is an isomorphism between `G2` and a subgraph of `G1`.
+Thus, to say that `G1` and `G2` are graph-subgraph isomorphic is to say
+that a subgraph of `G1` is isomorphic to `G2`.
+
+Other literature uses the phrase 'subgraph isomorphic' as in '`G1` does
+not have a subgraph isomorphic to `G2`'.  Another use is as an in adverb
+for isomorphic.  Thus, to say that `G1` and `G2` are subgraph isomorphic
+is to say that a subgraph of `G1` is isomorphic to `G2`.
+
+Finally, the term 'subgraph' can have multiple meanings. In this
+context, 'subgraph' always means a 'node-induced subgraph'. Edge-induced
+subgraph isomorphisms are not directly supported, but one should be
+able to perform the check by making use of
+:func:`line_graph <networkx.generators.line.line_graph>`. For
+subgraphs which are not induced, the term 'monomorphism' is preferred
+over 'isomorphism'.
+
+Let ``G = (N, E)`` be a graph with a set of nodes `N` and set of edges `E`.
+
+If ``G' = (N', E')`` is a subgraph, then:
+    `N'` is a subset of `N` and
+    `E'` is a subset of `E`.
+
+If ``G' = (N', E')`` is a node-induced subgraph, then:
+    `N'` is a subset of `N` and
+    `E'` is the subset of edges in `E` relating nodes in `N'`.
+
+If `G' = (N', E')` is an edge-induced subgraph, then:
+    `N'` is the subset of nodes in `N` related by edges in `E'` and
+    `E'` is a subset of `E`.
+
+If `G' = (N', E')` is a monomorphism, then:
+    `N'` is a subset of `N` and
+    `E'` is a subset of the set of edges in `E` relating nodes in `N'`.
+
+Note that if `G'` is a node-induced subgraph of `G`, then it is always a
+subgraph monomorphism of `G`, but the opposite is not always true, as a
+monomorphism can have fewer edges.
+
+References
+----------
+[1]   Luigi P. Cordella, Pasquale Foggia, Carlo Sansone, Mario Vento,
+      "A (Sub)Graph Isomorphism Algorithm for Matching Large Graphs",
+      IEEE Transactions on Pattern Analysis and Machine Intelligence,
+      vol. 26,  no. 10,  pp. 1367-1372,  Oct.,  2004.
+      http://ieeexplore.ieee.org/iel5/34/29305/01323804.pdf
+
+[2]   L. P. Cordella, P. Foggia, C. Sansone, M. Vento, "An Improved
+      Algorithm for Matching Large Graphs", 3rd IAPR-TC15 Workshop
+      on Graph-based Representations in Pattern Recognition, Cuen,
+      pp. 149-159, 2001.
+      https://www.researchgate.net/publication/200034365_An_Improved_Algorithm_for_Matching_Large_Graphs
+
+See Also
+--------
+:meth:`semantic_feasibility <networkx.algorithms.isomorphism.GraphMatcher.semantic_feasibility>`
+:meth:`syntactic_feasibility <networkx.algorithms.isomorphism.GraphMatcher.syntactic_feasibility>`
+
+Notes
+-----
+
+The implementation handles both directed and undirected graphs as well
+as multigraphs.
+
+In general, the subgraph isomorphism problem is NP-complete whereas the
+graph isomorphism problem is most likely not NP-complete (although no
+polynomial-time algorithm is known to exist).
+
+"""
+
+# This work was originally coded by Christopher Ellison
+# as part of the Computational Mechanics Python (CMPy) project.
+# James P. Crutchfield, principal investigator.
+# Complexity Sciences Center and Physics Department, UC Davis.
+
+import sys
+
+__all__ = ["GraphMatcher", "DiGraphMatcher"]
+
+
+class GraphMatcher:
+    """Implementation of VF2 algorithm for matching undirected graphs.
+
+    Suitable for Graph and MultiGraph instances.
+    """
+
+    def __init__(self, G1, G2):
+        """Initialize GraphMatcher.
+
+        Parameters
+        ----------
+        G1,G2: NetworkX Graph or MultiGraph instances.
+           The two graphs to check for isomorphism or monomorphism.
+
+        Examples
+        --------
+        To create a GraphMatcher which checks for syntactic feasibility:
+
+        >>> from networkx.algorithms import isomorphism
+        >>> G1 = nx.path_graph(4)
+        >>> G2 = nx.path_graph(4)
+        >>> GM = isomorphism.GraphMatcher(G1, G2)
+        """
+        self.G1 = G1
+        self.G2 = G2
+        self.G1_nodes = set(G1.nodes())
+        self.G2_nodes = set(G2.nodes())
+        self.G2_node_order = {n: i for i, n in enumerate(G2)}
+
+        # Set recursion limit.
+        self.old_recursion_limit = sys.getrecursionlimit()
+        expected_max_recursion_level = len(self.G2)
+        if self.old_recursion_limit < 1.5 * expected_max_recursion_level:
+            # Give some breathing room.
+            sys.setrecursionlimit(int(1.5 * expected_max_recursion_level))
+
+        # Declare that we will be searching for a graph-graph isomorphism.
+        self.test = "graph"
+
+        # Initialize state
+        self.initialize()
+
+    def reset_recursion_limit(self):
+        """Restores the recursion limit."""
+        # TODO:
+        # Currently, we use recursion and set the recursion level higher.
+        # It would be nice to restore the level, but because the
+        # (Di)GraphMatcher classes make use of cyclic references, garbage
+        # collection will never happen when we define __del__() to
+        # restore the recursion level. The result is a memory leak.
+        # So for now, we do not automatically restore the recursion level,
+        # and instead provide a method to do this manually. Eventually,
+        # we should turn this into a non-recursive implementation.
+        sys.setrecursionlimit(self.old_recursion_limit)
+
+    def candidate_pairs_iter(self):
+        """Iterator over candidate pairs of nodes in G1 and G2."""
+
+        # All computations are done using the current state!
+
+        G1_nodes = self.G1_nodes
+        G2_nodes = self.G2_nodes
+        min_key = self.G2_node_order.__getitem__
+
+        # First we compute the inout-terminal sets.
+        T1_inout = [node for node in self.inout_1 if node not in self.core_1]
+        T2_inout = [node for node in self.inout_2 if node not in self.core_2]
+
+        # If T1_inout and T2_inout are both nonempty.
+        # P(s) = T1_inout x {min T2_inout}
+        if T1_inout and T2_inout:
+            node_2 = min(T2_inout, key=min_key)
+            for node_1 in T1_inout:
+                yield node_1, node_2
+
+        else:
+            # If T1_inout and T2_inout were both empty....
+            # P(s) = (N_1 - M_1) x {min (N_2 - M_2)}
+            # if not (T1_inout or T2_inout):  # as suggested by  [2], incorrect
+            if 1:  # as inferred from [1], correct
+                # First we determine the candidate node for G2
+                other_node = min(G2_nodes - set(self.core_2), key=min_key)
+                for node in self.G1:
+                    if node not in self.core_1:
+                        yield node, other_node
+
+        # For all other cases, we don't have any candidate pairs.
+
+    def initialize(self):
+        """Reinitializes the state of the algorithm.
+
+        This method should be redefined if using something other than GMState.
+        If only subclassing GraphMatcher, a redefinition is not necessary.
+
+        """
+
+        # core_1[n] contains the index of the node paired with n, which is m,
+        #           provided n is in the mapping.
+        # core_2[m] contains the index of the node paired with m, which is n,
+        #           provided m is in the mapping.
+        self.core_1 = {}
+        self.core_2 = {}
+
+        # See the paper for definitions of M_x and T_x^{y}
+
+        # inout_1[n]  is non-zero if n is in M_1 or in T_1^{inout}
+        # inout_2[m]  is non-zero if m is in M_2 or in T_2^{inout}
+        #
+        # The value stored is the depth of the SSR tree when the node became
+        # part of the corresponding set.
+        self.inout_1 = {}
+        self.inout_2 = {}
+        # Practically, these sets simply store the nodes in the subgraph.
+
+        self.state = GMState(self)
+
+        # Provide a convenient way to access the isomorphism mapping.
+        self.mapping = self.core_1.copy()
+
+    def is_isomorphic(self):
+        """Returns True if G1 and G2 are isomorphic graphs."""
+
+        # Let's do two very quick checks!
+        # QUESTION: Should we call faster_graph_could_be_isomorphic(G1,G2)?
+        # For now, I just copy the code.
+
+        # Check global properties
+        if self.G1.order() != self.G2.order():
+            return False
+
+        # Check local properties
+        d1 = sorted(d for n, d in self.G1.degree())
+        d2 = sorted(d for n, d in self.G2.degree())
+        if d1 != d2:
+            return False
+
+        try:
+            x = next(self.isomorphisms_iter())
+            return True
+        except StopIteration:
+            return False
+
+    def isomorphisms_iter(self):
+        """Generator over isomorphisms between G1 and G2."""
+        # Declare that we are looking for a graph-graph isomorphism.
+        self.test = "graph"
+        self.initialize()
+        yield from self.match()
+
+    def match(self):
+        """Extends the isomorphism mapping.
+
+        This function is called recursively to determine if a complete
+        isomorphism can be found between G1 and G2.  It cleans up the class
+        variables after each recursive call. If an isomorphism is found,
+        we yield the mapping.
+
+        """
+        if len(self.core_1) == len(self.G2):
+            # Save the final mapping, otherwise garbage collection deletes it.
+            self.mapping = self.core_1.copy()
+            # The mapping is complete.
+            yield self.mapping
+        else:
+            for G1_node, G2_node in self.candidate_pairs_iter():
+                if self.syntactic_feasibility(G1_node, G2_node):
+                    if self.semantic_feasibility(G1_node, G2_node):
+                        # Recursive call, adding the feasible state.
+                        newstate = self.state.__class__(self, G1_node, G2_node)
+                        yield from self.match()
+
+                        # restore data structures
+                        newstate.restore()
+
+    def semantic_feasibility(self, G1_node, G2_node):
+        """Returns True if adding (G1_node, G2_node) is semantically feasible.
+
+        The semantic feasibility function should return True if it is
+        acceptable to add the candidate pair (G1_node, G2_node) to the current
+        partial isomorphism mapping.   The logic should focus on semantic
+        information contained in the edge data or a formalized node class.
+
+        By acceptable, we mean that the subsequent mapping can still become a
+        complete isomorphism mapping.  Thus, if adding the candidate pair
+        definitely makes it so that the subsequent mapping cannot become a
+        complete isomorphism mapping, then this function must return False.
+
+        The default semantic feasibility function always returns True. The
+        effect is that semantics are not considered in the matching of G1
+        and G2.
+
+        The semantic checks might differ based on the what type of test is
+        being performed.  A keyword description of the test is stored in
+        self.test.  Here is a quick description of the currently implemented
+        tests::
+
+          test='graph'
+            Indicates that the graph matcher is looking for a graph-graph
+            isomorphism.
+
+          test='subgraph'
+            Indicates that the graph matcher is looking for a subgraph-graph
+            isomorphism such that a subgraph of G1 is isomorphic to G2.
+
+          test='mono'
+            Indicates that the graph matcher is looking for a subgraph-graph
+            monomorphism such that a subgraph of G1 is monomorphic to G2.
+
+        Any subclass which redefines semantic_feasibility() must maintain
+        the above form to keep the match() method functional. Implementations
+        should consider multigraphs.
+        """
+        return True
+
+    def subgraph_is_isomorphic(self):
+        """Returns True if a subgraph of G1 is isomorphic to G2."""
+        try:
+            x = next(self.subgraph_isomorphisms_iter())
+            return True
+        except StopIteration:
+            return False
+
+    def subgraph_is_monomorphic(self):
+        """Returns True if a subgraph of G1 is monomorphic to G2."""
+        try:
+            x = next(self.subgraph_monomorphisms_iter())
+            return True
+        except StopIteration:
+            return False
+
+    #    subgraph_is_isomorphic.__doc__ += "\n" + subgraph.replace('\n','\n'+indent)
+
+    def subgraph_isomorphisms_iter(self):
+        """Generator over isomorphisms between a subgraph of G1 and G2."""
+        # Declare that we are looking for graph-subgraph isomorphism.
+        self.test = "subgraph"
+        self.initialize()
+        yield from self.match()
+
+    def subgraph_monomorphisms_iter(self):
+        """Generator over monomorphisms between a subgraph of G1 and G2."""
+        # Declare that we are looking for graph-subgraph monomorphism.
+        self.test = "mono"
+        self.initialize()
+        yield from self.match()
+
+    #    subgraph_isomorphisms_iter.__doc__ += "\n" + subgraph.replace('\n','\n'+indent)
+
+    def syntactic_feasibility(self, G1_node, G2_node):
+        """Returns True if adding (G1_node, G2_node) is syntactically feasible.
+
+        This function returns True if it is adding the candidate pair
+        to the current partial isomorphism/monomorphism mapping is allowable.
+        The addition is allowable if the inclusion of the candidate pair does
+        not make it impossible for an isomorphism/monomorphism to be found.
+        """
+
+        # The VF2 algorithm was designed to work with graphs having, at most,
+        # one edge connecting any two nodes.  This is not the case when
+        # dealing with an MultiGraphs.
+        #
+        # Basically, when we test the look-ahead rules R_neighbor, we will
+        # make sure that the number of edges are checked. We also add
+        # a R_self check to verify that the number of selfloops is acceptable.
+        #
+        # Users might be comparing Graph instances with MultiGraph instances.
+        # So the generic GraphMatcher class must work with MultiGraphs.
+        # Care must be taken since the value in the innermost dictionary is a
+        # singlet for Graph instances.  For MultiGraphs, the value in the
+        # innermost dictionary is a list.
+
+        ###
+        # Test at each step to get a return value as soon as possible.
+        ###
+
+        # Look ahead 0
+
+        # R_self
+
+        # The number of selfloops for G1_node must equal the number of
+        # self-loops for G2_node. Without this check, we would fail on
+        # R_neighbor at the next recursion level. But it is good to prune the
+        # search tree now.
+
+        if self.test == "mono":
+            if self.G1.number_of_edges(G1_node, G1_node) < self.G2.number_of_edges(
+                G2_node, G2_node
+            ):
+                return False
+        else:
+            if self.G1.number_of_edges(G1_node, G1_node) != self.G2.number_of_edges(
+                G2_node, G2_node
+            ):
+                return False
+
+        # R_neighbor
+
+        # For each neighbor n' of n in the partial mapping, the corresponding
+        # node m' is a neighbor of m, and vice versa. Also, the number of
+        # edges must be equal.
+        if self.test != "mono":
+            for neighbor in self.G1[G1_node]:
+                if neighbor in self.core_1:
+                    if self.core_1[neighbor] not in self.G2[G2_node]:
+                        return False
+                    elif self.G1.number_of_edges(
+                        neighbor, G1_node
+                    ) != self.G2.number_of_edges(self.core_1[neighbor], G2_node):
+                        return False
+
+        for neighbor in self.G2[G2_node]:
+            if neighbor in self.core_2:
+                if self.core_2[neighbor] not in self.G1[G1_node]:
+                    return False
+                elif self.test == "mono":
+                    if self.G1.number_of_edges(
+                        self.core_2[neighbor], G1_node
+                    ) < self.G2.number_of_edges(neighbor, G2_node):
+                        return False
+                else:
+                    if self.G1.number_of_edges(
+                        self.core_2[neighbor], G1_node
+                    ) != self.G2.number_of_edges(neighbor, G2_node):
+                        return False
+
+        if self.test != "mono":
+            # Look ahead 1
+
+            # R_terminout
+            # The number of neighbors of n in T_1^{inout} is equal to the
+            # number of neighbors of m that are in T_2^{inout}, and vice versa.
+            num1 = 0
+            for neighbor in self.G1[G1_node]:
+                if (neighbor in self.inout_1) and (neighbor not in self.core_1):
+                    num1 += 1
+            num2 = 0
+            for neighbor in self.G2[G2_node]:
+                if (neighbor in self.inout_2) and (neighbor not in self.core_2):
+                    num2 += 1
+            if self.test == "graph":
+                if num1 != num2:
+                    return False
+            else:  # self.test == 'subgraph'
+                if not (num1 >= num2):
+                    return False
+
+            # Look ahead 2
+
+            # R_new
+
+            # The number of neighbors of n that are neither in the core_1 nor
+            # T_1^{inout} is equal to the number of neighbors of m
+            # that are neither in core_2 nor T_2^{inout}.
+            num1 = 0
+            for neighbor in self.G1[G1_node]:
+                if neighbor not in self.inout_1:
+                    num1 += 1
+            num2 = 0
+            for neighbor in self.G2[G2_node]:
+                if neighbor not in self.inout_2:
+                    num2 += 1
+            if self.test == "graph":
+                if num1 != num2:
+                    return False
+            else:  # self.test == 'subgraph'
+                if not (num1 >= num2):
+                    return False
+
+        # Otherwise, this node pair is syntactically feasible!
+        return True
+
+
+class DiGraphMatcher(GraphMatcher):
+    """Implementation of VF2 algorithm for matching directed graphs.
+
+    Suitable for DiGraph and MultiDiGraph instances.
+    """
+
+    def __init__(self, G1, G2):
+        """Initialize DiGraphMatcher.
+
+        G1 and G2 should be nx.Graph or nx.MultiGraph instances.
+
+        Examples
+        --------
+        To create a GraphMatcher which checks for syntactic feasibility:
+
+        >>> from networkx.algorithms import isomorphism
+        >>> G1 = nx.DiGraph(nx.path_graph(4, create_using=nx.DiGraph()))
+        >>> G2 = nx.DiGraph(nx.path_graph(4, create_using=nx.DiGraph()))
+        >>> DiGM = isomorphism.DiGraphMatcher(G1, G2)
+        """
+        super().__init__(G1, G2)
+
+    def candidate_pairs_iter(self):
+        """Iterator over candidate pairs of nodes in G1 and G2."""
+
+        # All computations are done using the current state!
+
+        G1_nodes = self.G1_nodes
+        G2_nodes = self.G2_nodes
+        min_key = self.G2_node_order.__getitem__
+
+        # First we compute the out-terminal sets.
+        T1_out = [node for node in self.out_1 if node not in self.core_1]
+        T2_out = [node for node in self.out_2 if node not in self.core_2]
+
+        # If T1_out and T2_out are both nonempty.
+        # P(s) = T1_out x {min T2_out}
+        if T1_out and T2_out:
+            node_2 = min(T2_out, key=min_key)
+            for node_1 in T1_out:
+                yield node_1, node_2
+
+        # If T1_out and T2_out were both empty....
+        # We compute the in-terminal sets.
+
+        # elif not (T1_out or T2_out):   # as suggested by [2], incorrect
+        else:  # as suggested by [1], correct
+            T1_in = [node for node in self.in_1 if node not in self.core_1]
+            T2_in = [node for node in self.in_2 if node not in self.core_2]
+
+            # If T1_in and T2_in are both nonempty.
+            # P(s) = T1_out x {min T2_out}
+            if T1_in and T2_in:
+                node_2 = min(T2_in, key=min_key)
+                for node_1 in T1_in:
+                    yield node_1, node_2
+
+            # If all terminal sets are empty...
+            # P(s) = (N_1 - M_1) x {min (N_2 - M_2)}
+
+            # elif not (T1_in or T2_in):   # as suggested by  [2], incorrect
+            else:  # as inferred from [1], correct
+                node_2 = min(G2_nodes - set(self.core_2), key=min_key)
+                for node_1 in G1_nodes:
+                    if node_1 not in self.core_1:
+                        yield node_1, node_2
+
+        # For all other cases, we don't have any candidate pairs.
+
+    def initialize(self):
+        """Reinitializes the state of the algorithm.
+
+        This method should be redefined if using something other than DiGMState.
+        If only subclassing GraphMatcher, a redefinition is not necessary.
+        """
+
+        # core_1[n] contains the index of the node paired with n, which is m,
+        #           provided n is in the mapping.
+        # core_2[m] contains the index of the node paired with m, which is n,
+        #           provided m is in the mapping.
+        self.core_1 = {}
+        self.core_2 = {}
+
+        # See the paper for definitions of M_x and T_x^{y}
+
+        # in_1[n]  is non-zero if n is in M_1 or in T_1^{in}
+        # out_1[n] is non-zero if n is in M_1 or in T_1^{out}
+        #
+        # in_2[m]  is non-zero if m is in M_2 or in T_2^{in}
+        # out_2[m] is non-zero if m is in M_2 or in T_2^{out}
+        #
+        # The value stored is the depth of the search tree when the node became
+        # part of the corresponding set.
+        self.in_1 = {}
+        self.in_2 = {}
+        self.out_1 = {}
+        self.out_2 = {}
+
+        self.state = DiGMState(self)
+
+        # Provide a convenient way to access the isomorphism mapping.
+        self.mapping = self.core_1.copy()
+
+    def syntactic_feasibility(self, G1_node, G2_node):
+        """Returns True if adding (G1_node, G2_node) is syntactically feasible.
+
+        This function returns True if it is adding the candidate pair
+        to the current partial isomorphism/monomorphism mapping is allowable.
+        The addition is allowable if the inclusion of the candidate pair does
+        not make it impossible for an isomorphism/monomorphism to be found.
+        """
+
+        # The VF2 algorithm was designed to work with graphs having, at most,
+        # one edge connecting any two nodes.  This is not the case when
+        # dealing with an MultiGraphs.
+        #
+        # Basically, when we test the look-ahead rules R_pred and R_succ, we
+        # will make sure that the number of edges are checked.  We also add
+        # a R_self check to verify that the number of selfloops is acceptable.
+
+        # Users might be comparing DiGraph instances with MultiDiGraph
+        # instances. So the generic DiGraphMatcher class must work with
+        # MultiDiGraphs. Care must be taken since the value in the innermost
+        # dictionary is a singlet for DiGraph instances.  For MultiDiGraphs,
+        # the value in the innermost dictionary is a list.
+
+        ###
+        # Test at each step to get a return value as soon as possible.
+        ###
+
+        # Look ahead 0
+
+        # R_self
+
+        # The number of selfloops for G1_node must equal the number of
+        # self-loops for G2_node. Without this check, we would fail on R_pred
+        # at the next recursion level. This should prune the tree even further.
+        if self.test == "mono":
+            if self.G1.number_of_edges(G1_node, G1_node) < self.G2.number_of_edges(
+                G2_node, G2_node
+            ):
+                return False
+        else:
+            if self.G1.number_of_edges(G1_node, G1_node) != self.G2.number_of_edges(
+                G2_node, G2_node
+            ):
+                return False
+
+        # R_pred
+
+        # For each predecessor n' of n in the partial mapping, the
+        # corresponding node m' is a predecessor of m, and vice versa. Also,
+        # the number of edges must be equal
+        if self.test != "mono":
+            for predecessor in self.G1.pred[G1_node]:
+                if predecessor in self.core_1:
+                    if self.core_1[predecessor] not in self.G2.pred[G2_node]:
+                        return False
+                    elif self.G1.number_of_edges(
+                        predecessor, G1_node
+                    ) != self.G2.number_of_edges(self.core_1[predecessor], G2_node):
+                        return False
+
+        for predecessor in self.G2.pred[G2_node]:
+            if predecessor in self.core_2:
+                if self.core_2[predecessor] not in self.G1.pred[G1_node]:
+                    return False
+                elif self.test == "mono":
+                    if self.G1.number_of_edges(
+                        self.core_2[predecessor], G1_node
+                    ) < self.G2.number_of_edges(predecessor, G2_node):
+                        return False
+                else:
+                    if self.G1.number_of_edges(
+                        self.core_2[predecessor], G1_node
+                    ) != self.G2.number_of_edges(predecessor, G2_node):
+                        return False
+
+        # R_succ
+
+        # For each successor n' of n in the partial mapping, the corresponding
+        # node m' is a successor of m, and vice versa. Also, the number of
+        # edges must be equal.
+        if self.test != "mono":
+            for successor in self.G1[G1_node]:
+                if successor in self.core_1:
+                    if self.core_1[successor] not in self.G2[G2_node]:
+                        return False
+                    elif self.G1.number_of_edges(
+                        G1_node, successor
+                    ) != self.G2.number_of_edges(G2_node, self.core_1[successor]):
+                        return False
+
+        for successor in self.G2[G2_node]:
+            if successor in self.core_2:
+                if self.core_2[successor] not in self.G1[G1_node]:
+                    return False
+                elif self.test == "mono":
+                    if self.G1.number_of_edges(
+                        G1_node, self.core_2[successor]
+                    ) < self.G2.number_of_edges(G2_node, successor):
+                        return False
+                else:
+                    if self.G1.number_of_edges(
+                        G1_node, self.core_2[successor]
+                    ) != self.G2.number_of_edges(G2_node, successor):
+                        return False
+
+        if self.test != "mono":
+            # Look ahead 1
+
+            # R_termin
+            # The number of predecessors of n that are in T_1^{in} is equal to the
+            # number of predecessors of m that are in T_2^{in}.
+            num1 = 0
+            for predecessor in self.G1.pred[G1_node]:
+                if (predecessor in self.in_1) and (predecessor not in self.core_1):
+                    num1 += 1
+            num2 = 0
+            for predecessor in self.G2.pred[G2_node]:
+                if (predecessor in self.in_2) and (predecessor not in self.core_2):
+                    num2 += 1
+            if self.test == "graph":
+                if num1 != num2:
+                    return False
+            else:  # self.test == 'subgraph'
+                if not (num1 >= num2):
+                    return False
+
+            # The number of successors of n that are in T_1^{in} is equal to the
+            # number of successors of m that are in T_2^{in}.
+            num1 = 0
+            for successor in self.G1[G1_node]:
+                if (successor in self.in_1) and (successor not in self.core_1):
+                    num1 += 1
+            num2 = 0
+            for successor in self.G2[G2_node]:
+                if (successor in self.in_2) and (successor not in self.core_2):
+                    num2 += 1
+            if self.test == "graph":
+                if num1 != num2:
+                    return False
+            else:  # self.test == 'subgraph'
+                if not (num1 >= num2):
+                    return False
+
+            # R_termout
+
+            # The number of predecessors of n that are in T_1^{out} is equal to the
+            # number of predecessors of m that are in T_2^{out}.
+            num1 = 0
+            for predecessor in self.G1.pred[G1_node]:
+                if (predecessor in self.out_1) and (predecessor not in self.core_1):
+                    num1 += 1
+            num2 = 0
+            for predecessor in self.G2.pred[G2_node]:
+                if (predecessor in self.out_2) and (predecessor not in self.core_2):
+                    num2 += 1
+            if self.test == "graph":
+                if num1 != num2:
+                    return False
+            else:  # self.test == 'subgraph'
+                if not (num1 >= num2):
+                    return False
+
+            # The number of successors of n that are in T_1^{out} is equal to the
+            # number of successors of m that are in T_2^{out}.
+            num1 = 0
+            for successor in self.G1[G1_node]:
+                if (successor in self.out_1) and (successor not in self.core_1):
+                    num1 += 1
+            num2 = 0
+            for successor in self.G2[G2_node]:
+                if (successor in self.out_2) and (successor not in self.core_2):
+                    num2 += 1
+            if self.test == "graph":
+                if num1 != num2:
+                    return False
+            else:  # self.test == 'subgraph'
+                if not (num1 >= num2):
+                    return False
+
+            # Look ahead 2
+
+            # R_new
+
+            # The number of predecessors of n that are neither in the core_1 nor
+            # T_1^{in} nor T_1^{out} is equal to the number of predecessors of m
+            # that are neither in core_2 nor T_2^{in} nor T_2^{out}.
+            num1 = 0
+            for predecessor in self.G1.pred[G1_node]:
+                if (predecessor not in self.in_1) and (predecessor not in self.out_1):
+                    num1 += 1
+            num2 = 0
+            for predecessor in self.G2.pred[G2_node]:
+                if (predecessor not in self.in_2) and (predecessor not in self.out_2):
+                    num2 += 1
+            if self.test == "graph":
+                if num1 != num2:
+                    return False
+            else:  # self.test == 'subgraph'
+                if not (num1 >= num2):
+                    return False
+
+            # The number of successors of n that are neither in the core_1 nor
+            # T_1^{in} nor T_1^{out} is equal to the number of successors of m
+            # that are neither in core_2 nor T_2^{in} nor T_2^{out}.
+            num1 = 0
+            for successor in self.G1[G1_node]:
+                if (successor not in self.in_1) and (successor not in self.out_1):
+                    num1 += 1
+            num2 = 0
+            for successor in self.G2[G2_node]:
+                if (successor not in self.in_2) and (successor not in self.out_2):
+                    num2 += 1
+            if self.test == "graph":
+                if num1 != num2:
+                    return False
+            else:  # self.test == 'subgraph'
+                if not (num1 >= num2):
+                    return False
+
+        # Otherwise, this node pair is syntactically feasible!
+        return True
+
+
+class GMState:
+    """Internal representation of state for the GraphMatcher class.
+
+    This class is used internally by the GraphMatcher class.  It is used
+    only to store state specific data. There will be at most G2.order() of
+    these objects in memory at a time, due to the depth-first search
+    strategy employed by the VF2 algorithm.
+    """
+
+    def __init__(self, GM, G1_node=None, G2_node=None):
+        """Initializes GMState object.
+
+        Pass in the GraphMatcher to which this GMState belongs and the
+        new node pair that will be added to the GraphMatcher's current
+        isomorphism mapping.
+        """
+        self.GM = GM
+
+        # Initialize the last stored node pair.
+        self.G1_node = None
+        self.G2_node = None
+        self.depth = len(GM.core_1)
+
+        if G1_node is None or G2_node is None:
+            # Then we reset the class variables
+            GM.core_1 = {}
+            GM.core_2 = {}
+            GM.inout_1 = {}
+            GM.inout_2 = {}
+
+        # Watch out! G1_node == 0 should evaluate to True.
+        if G1_node is not None and G2_node is not None:
+            # Add the node pair to the isomorphism mapping.
+            GM.core_1[G1_node] = G2_node
+            GM.core_2[G2_node] = G1_node
+
+            # Store the node that was added last.
+            self.G1_node = G1_node
+            self.G2_node = G2_node
+
+            # Now we must update the other two vectors.
+            # We will add only if it is not in there already!
+            self.depth = len(GM.core_1)
+
+            # First we add the new nodes...
+            if G1_node not in GM.inout_1:
+                GM.inout_1[G1_node] = self.depth
+            if G2_node not in GM.inout_2:
+                GM.inout_2[G2_node] = self.depth
+
+            # Now we add every other node...
+
+            # Updates for T_1^{inout}
+            new_nodes = set()
+            for node in GM.core_1:
+                new_nodes.update(
+                    [neighbor for neighbor in GM.G1[node] if neighbor not in GM.core_1]
+                )
+            for node in new_nodes:
+                if node not in GM.inout_1:
+                    GM.inout_1[node] = self.depth
+
+            # Updates for T_2^{inout}
+            new_nodes = set()
+            for node in GM.core_2:
+                new_nodes.update(
+                    [neighbor for neighbor in GM.G2[node] if neighbor not in GM.core_2]
+                )
+            for node in new_nodes:
+                if node not in GM.inout_2:
+                    GM.inout_2[node] = self.depth
+
+    def restore(self):
+        """Deletes the GMState object and restores the class variables."""
+        # First we remove the node that was added from the core vectors.
+        # Watch out! G1_node == 0 should evaluate to True.
+        if self.G1_node is not None and self.G2_node is not None:
+            del self.GM.core_1[self.G1_node]
+            del self.GM.core_2[self.G2_node]
+
+        # Now we revert the other two vectors.
+        # Thus, we delete all entries which have this depth level.
+        for vector in (self.GM.inout_1, self.GM.inout_2):
+            for node in list(vector.keys()):
+                if vector[node] == self.depth:
+                    del vector[node]
+
+
+class DiGMState:
+    """Internal representation of state for the DiGraphMatcher class.
+
+    This class is used internally by the DiGraphMatcher class.  It is used
+    only to store state specific data. There will be at most G2.order() of
+    these objects in memory at a time, due to the depth-first search
+    strategy employed by the VF2 algorithm.
+
+    """
+
+    def __init__(self, GM, G1_node=None, G2_node=None):
+        """Initializes DiGMState object.
+
+        Pass in the DiGraphMatcher to which this DiGMState belongs and the
+        new node pair that will be added to the GraphMatcher's current
+        isomorphism mapping.
+        """
+        self.GM = GM
+
+        # Initialize the last stored node pair.
+        self.G1_node = None
+        self.G2_node = None
+        self.depth = len(GM.core_1)
+
+        if G1_node is None or G2_node is None:
+            # Then we reset the class variables
+            GM.core_1 = {}
+            GM.core_2 = {}
+            GM.in_1 = {}
+            GM.in_2 = {}
+            GM.out_1 = {}
+            GM.out_2 = {}
+
+        # Watch out! G1_node == 0 should evaluate to True.
+        if G1_node is not None and G2_node is not None:
+            # Add the node pair to the isomorphism mapping.
+            GM.core_1[G1_node] = G2_node
+            GM.core_2[G2_node] = G1_node
+
+            # Store the node that was added last.
+            self.G1_node = G1_node
+            self.G2_node = G2_node
+
+            # Now we must update the other four vectors.
+            # We will add only if it is not in there already!
+            self.depth = len(GM.core_1)
+
+            # First we add the new nodes...
+            for vector in (GM.in_1, GM.out_1):
+                if G1_node not in vector:
+                    vector[G1_node] = self.depth
+            for vector in (GM.in_2, GM.out_2):
+                if G2_node not in vector:
+                    vector[G2_node] = self.depth
+
+            # Now we add every other node...
+
+            # Updates for T_1^{in}
+            new_nodes = set()
+            for node in GM.core_1:
+                new_nodes.update(
+                    [
+                        predecessor
+                        for predecessor in GM.G1.predecessors(node)
+                        if predecessor not in GM.core_1
+                    ]
+                )
+            for node in new_nodes:
+                if node not in GM.in_1:
+                    GM.in_1[node] = self.depth
+
+            # Updates for T_2^{in}
+            new_nodes = set()
+            for node in GM.core_2:
+                new_nodes.update(
+                    [
+                        predecessor
+                        for predecessor in GM.G2.predecessors(node)
+                        if predecessor not in GM.core_2
+                    ]
+                )
+            for node in new_nodes:
+                if node not in GM.in_2:
+                    GM.in_2[node] = self.depth
+
+            # Updates for T_1^{out}
+            new_nodes = set()
+            for node in GM.core_1:
+                new_nodes.update(
+                    [
+                        successor
+                        for successor in GM.G1.successors(node)
+                        if successor not in GM.core_1
+                    ]
+                )
+            for node in new_nodes:
+                if node not in GM.out_1:
+                    GM.out_1[node] = self.depth
+
+            # Updates for T_2^{out}
+            new_nodes = set()
+            for node in GM.core_2:
+                new_nodes.update(
+                    [
+                        successor
+                        for successor in GM.G2.successors(node)
+                        if successor not in GM.core_2
+                    ]
+                )
+            for node in new_nodes:
+                if node not in GM.out_2:
+                    GM.out_2[node] = self.depth
+
+    def restore(self):
+        """Deletes the DiGMState object and restores the class variables."""
+
+        # First we remove the node that was added from the core vectors.
+        # Watch out! G1_node == 0 should evaluate to True.
+        if self.G1_node is not None and self.G2_node is not None:
+            del self.GM.core_1[self.G1_node]
+            del self.GM.core_2[self.G2_node]
+
+        # Now we revert the other four vectors.
+        # Thus, we delete all entries which have this depth level.
+        for vector in (self.GM.in_1, self.GM.in_2, self.GM.out_1, self.GM.out_2):
+            for node in list(vector.keys()):
+                if vector[node] == self.depth:
+                    del vector[node]

venv/lib/python3.10/site-packages/networkx/algorithms/isomorphism/matchhelpers.py

@@ -0,0 +1,351 @@
+"""Functions which help end users define customize node_match and
+edge_match functions to use during isomorphism checks.
+"""
+import math
+import types
+from itertools import permutations
+
+__all__ = [
+    "categorical_node_match",
+    "categorical_edge_match",
+    "categorical_multiedge_match",
+    "numerical_node_match",
+    "numerical_edge_match",
+    "numerical_multiedge_match",
+    "generic_node_match",
+    "generic_edge_match",
+    "generic_multiedge_match",
+]
+
+
+def copyfunc(f, name=None):
+    """Returns a deepcopy of a function."""
+    return types.FunctionType(
+        f.__code__, f.__globals__, name or f.__name__, f.__defaults__, f.__closure__
+    )
+
+
+def allclose(x, y, rtol=1.0000000000000001e-05, atol=1e-08):
+    """Returns True if x and y are sufficiently close, elementwise.
+
+    Parameters
+    ----------
+    rtol : float
+        The relative error tolerance.
+    atol : float
+        The absolute error tolerance.
+
+    """
+    # assume finite weights, see numpy.allclose() for reference
+    return all(math.isclose(xi, yi, rel_tol=rtol, abs_tol=atol) for xi, yi in zip(x, y))
+
+
+categorical_doc = """
+Returns a comparison function for a categorical node attribute.
+
+The value(s) of the attr(s) must be hashable and comparable via the ==
+operator since they are placed into a set([]) object.  If the sets from
+G1 and G2 are the same, then the constructed function returns True.
+
+Parameters
+----------
+attr : string | list
+    The categorical node attribute to compare, or a list of categorical
+    node attributes to compare.
+default : value | list
+    The default value for the categorical node attribute, or a list of
+    default values for the categorical node attributes.
+
+Returns
+-------
+match : function
+    The customized, categorical `node_match` function.
+
+Examples
+--------
+>>> import networkx.algorithms.isomorphism as iso
+>>> nm = iso.categorical_node_match("size", 1)
+>>> nm = iso.categorical_node_match(["color", "size"], ["red", 2])
+
+"""
+
+
+def categorical_node_match(attr, default):
+    if isinstance(attr, str):
+
+        def match(data1, data2):
+            return data1.get(attr, default) == data2.get(attr, default)
+
+    else:
+        attrs = list(zip(attr, default))  # Python 3
+
+        def match(data1, data2):
+            return all(data1.get(attr, d) == data2.get(attr, d) for attr, d in attrs)
+
+    return match
+
+
+categorical_edge_match = copyfunc(categorical_node_match, "categorical_edge_match")
+
+
+def categorical_multiedge_match(attr, default):
+    if isinstance(attr, str):
+
+        def match(datasets1, datasets2):
+            values1 = {data.get(attr, default) for data in datasets1.values()}
+            values2 = {data.get(attr, default) for data in datasets2.values()}
+            return values1 == values2
+
+    else:
+        attrs = list(zip(attr, default))  # Python 3
+
+        def match(datasets1, datasets2):
+            values1 = set()
+            for data1 in datasets1.values():
+                x = tuple(data1.get(attr, d) for attr, d in attrs)
+                values1.add(x)
+            values2 = set()
+            for data2 in datasets2.values():
+                x = tuple(data2.get(attr, d) for attr, d in attrs)
+                values2.add(x)
+            return values1 == values2
+
+    return match
+
+
+# Docstrings for categorical functions.
+categorical_node_match.__doc__ = categorical_doc
+categorical_edge_match.__doc__ = categorical_doc.replace("node", "edge")
+tmpdoc = categorical_doc.replace("node", "edge")
+tmpdoc = tmpdoc.replace("categorical_edge_match", "categorical_multiedge_match")
+categorical_multiedge_match.__doc__ = tmpdoc
+
+
+numerical_doc = """
+Returns a comparison function for a numerical node attribute.
+
+The value(s) of the attr(s) must be numerical and sortable.  If the
+sorted list of values from G1 and G2 are the same within some
+tolerance, then the constructed function returns True.
+
+Parameters
+----------
+attr : string | list
+    The numerical node attribute to compare, or a list of numerical
+    node attributes to compare.
+default : value | list
+    The default value for the numerical node attribute, or a list of
+    default values for the numerical node attributes.
+rtol : float
+    The relative error tolerance.
+atol : float
+    The absolute error tolerance.
+
+Returns
+-------
+match : function
+    The customized, numerical `node_match` function.
+
+Examples
+--------
+>>> import networkx.algorithms.isomorphism as iso
+>>> nm = iso.numerical_node_match("weight", 1.0)
+>>> nm = iso.numerical_node_match(["weight", "linewidth"], [0.25, 0.5])
+
+"""
+
+
+def numerical_node_match(attr, default, rtol=1.0000000000000001e-05, atol=1e-08):
+    if isinstance(attr, str):
+
+        def match(data1, data2):
+            return math.isclose(
+                data1.get(attr, default),
+                data2.get(attr, default),
+                rel_tol=rtol,
+                abs_tol=atol,
+            )
+
+    else:
+        attrs = list(zip(attr, default))  # Python 3
+
+        def match(data1, data2):
+            values1 = [data1.get(attr, d) for attr, d in attrs]
+            values2 = [data2.get(attr, d) for attr, d in attrs]
+            return allclose(values1, values2, rtol=rtol, atol=atol)
+
+    return match
+
+
+numerical_edge_match = copyfunc(numerical_node_match, "numerical_edge_match")
+
+
+def numerical_multiedge_match(attr, default, rtol=1.0000000000000001e-05, atol=1e-08):
+    if isinstance(attr, str):
+
+        def match(datasets1, datasets2):
+            values1 = sorted(data.get(attr, default) for data in datasets1.values())
+            values2 = sorted(data.get(attr, default) for data in datasets2.values())
+            return allclose(values1, values2, rtol=rtol, atol=atol)
+
+    else:
+        attrs = list(zip(attr, default))  # Python 3
+
+        def match(datasets1, datasets2):
+            values1 = []
+            for data1 in datasets1.values():
+                x = tuple(data1.get(attr, d) for attr, d in attrs)
+                values1.append(x)
+            values2 = []
+            for data2 in datasets2.values():
+                x = tuple(data2.get(attr, d) for attr, d in attrs)
+                values2.append(x)
+            values1.sort()
+            values2.sort()
+            for xi, yi in zip(values1, values2):
+                if not allclose(xi, yi, rtol=rtol, atol=atol):
+                    return False
+            else:
+                return True
+
+    return match
+
+
+# Docstrings for numerical functions.
+numerical_node_match.__doc__ = numerical_doc
+numerical_edge_match.__doc__ = numerical_doc.replace("node", "edge")
+tmpdoc = numerical_doc.replace("node", "edge")
+tmpdoc = tmpdoc.replace("numerical_edge_match", "numerical_multiedge_match")
+numerical_multiedge_match.__doc__ = tmpdoc
+
+
+generic_doc = """
+Returns a comparison function for a generic attribute.
+
+The value(s) of the attr(s) are compared using the specified
+operators. If all the attributes are equal, then the constructed
+function returns True.
+
+Parameters
+----------
+attr : string | list
+    The node attribute to compare, or a list of node attributes
+    to compare.
+default : value | list
+    The default value for the node attribute, or a list of
+    default values for the node attributes.
+op : callable | list
+    The operator to use when comparing attribute values, or a list
+    of operators to use when comparing values for each attribute.
+
+Returns
+-------
+match : function
+    The customized, generic `node_match` function.
+
+Examples
+--------
+>>> from operator import eq
+>>> from math import isclose
+>>> from networkx.algorithms.isomorphism import generic_node_match
+>>> nm = generic_node_match("weight", 1.0, isclose)
+>>> nm = generic_node_match("color", "red", eq)
+>>> nm = generic_node_match(["weight", "color"], [1.0, "red"], [isclose, eq])
+
+"""
+
+
+def generic_node_match(attr, default, op):
+    if isinstance(attr, str):
+
+        def match(data1, data2):
+            return op(data1.get(attr, default), data2.get(attr, default))
+
+    else:
+        attrs = list(zip(attr, default, op))  # Python 3
+
+        def match(data1, data2):
+            for attr, d, operator in attrs:
+                if not operator(data1.get(attr, d), data2.get(attr, d)):
+                    return False
+            else:
+                return True
+
+    return match
+
+
+generic_edge_match = copyfunc(generic_node_match, "generic_edge_match")
+
+
+def generic_multiedge_match(attr, default, op):
+    """Returns a comparison function for a generic attribute.
+
+    The value(s) of the attr(s) are compared using the specified
+    operators. If all the attributes are equal, then the constructed
+    function returns True. Potentially, the constructed edge_match
+    function can be slow since it must verify that no isomorphism
+    exists between the multiedges before it returns False.
+
+    Parameters
+    ----------
+    attr : string | list
+        The edge attribute to compare, or a list of node attributes
+        to compare.
+    default : value | list
+        The default value for the edge attribute, or a list of
+        default values for the edgeattributes.
+    op : callable | list
+        The operator to use when comparing attribute values, or a list
+        of operators to use when comparing values for each attribute.
+
+    Returns
+    -------
+    match : function
+        The customized, generic `edge_match` function.
+
+    Examples
+    --------
+    >>> from operator import eq
+    >>> from math import isclose
+    >>> from networkx.algorithms.isomorphism import generic_node_match
+    >>> nm = generic_node_match("weight", 1.0, isclose)
+    >>> nm = generic_node_match("color", "red", eq)
+    >>> nm = generic_node_match(["weight", "color"], [1.0, "red"], [isclose, eq])
+
+    """
+
+    # This is slow, but generic.
+    # We must test every possible isomorphism between the edges.
+    if isinstance(attr, str):
+        attr = [attr]
+        default = [default]
+        op = [op]
+    attrs = list(zip(attr, default))  # Python 3
+
+    def match(datasets1, datasets2):
+        values1 = []
+        for data1 in datasets1.values():
+            x = tuple(data1.get(attr, d) for attr, d in attrs)
+            values1.append(x)
+        values2 = []
+        for data2 in datasets2.values():
+            x = tuple(data2.get(attr, d) for attr, d in attrs)
+            values2.append(x)
+        for vals2 in permutations(values2):
+            for xi, yi in zip(values1, vals2):
+                if not all(map(lambda x, y, z: z(x, y), xi, yi, op)):
+                    # This is not an isomorphism, go to next permutation.
+                    break
+            else:
+                # Then we found an isomorphism.
+                return True
+        else:
+            # Then there are no isomorphisms between the multiedges.
+            return False
+
+    return match
+
+
+# Docstrings for numerical functions.
+generic_node_match.__doc__ = generic_doc
+generic_edge_match.__doc__ = generic_doc.replace("node", "edge")

venv/lib/python3.10/site-packages/networkx/algorithms/isomorphism/temporalisomorphvf2.py

@@ -0,0 +1,304 @@
+"""
+*****************************
+Time-respecting VF2 Algorithm
+*****************************
+
+An extension of the VF2 algorithm for time-respecting graph isomorphism
+testing in temporal graphs.
+
+A temporal graph is one in which edges contain a datetime attribute,
+denoting when interaction occurred between the incident nodes. A
+time-respecting subgraph of a temporal graph is a subgraph such that
+all interactions incident to a node occurred within a time threshold,
+delta, of each other. A directed time-respecting subgraph has the
+added constraint that incoming interactions to a node must precede
+outgoing interactions from the same node - this enforces a sense of
+directed flow.
+
+Introduction
+------------
+
+The TimeRespectingGraphMatcher and TimeRespectingDiGraphMatcher
+extend the GraphMatcher and DiGraphMatcher classes, respectively,
+to include temporal constraints on matches. This is achieved through
+a semantic check, via the semantic_feasibility() function.
+
+As well as including G1 (the graph in which to seek embeddings) and
+G2 (the subgraph structure of interest), the name of the temporal
+attribute on the edges and the time threshold, delta, must be supplied
+as arguments to the matching constructors.
+
+A delta of zero is the strictest temporal constraint on the match -
+only embeddings in which all interactions occur at the same time will
+be returned. A delta of one day will allow embeddings in which
+adjacent interactions occur up to a day apart.
+
+Examples
+--------
+
+Examples will be provided when the datetime type has been incorporated.
+
+
+Temporal Subgraph Isomorphism
+-----------------------------
+
+A brief discussion of the somewhat diverse current literature will be
+included here.
+
+References
+----------
+
+[1] Redmond, U. and Cunningham, P. Temporal subgraph isomorphism. In:
+The 2013 IEEE/ACM International Conference on Advances in Social
+Networks Analysis and Mining (ASONAM). Niagara Falls, Canada; 2013:
+pages 1451 - 1452. [65]
+
+For a discussion of the literature on temporal networks:
+
+[3] P. Holme and J. Saramaki. Temporal networks. Physics Reports,
+519(3):97–125, 2012.
+
+Notes
+-----
+
+Handles directed and undirected graphs and graphs with parallel edges.
+
+"""
+
+import networkx as nx
+
+from .isomorphvf2 import DiGraphMatcher, GraphMatcher
+
+__all__ = ["TimeRespectingGraphMatcher", "TimeRespectingDiGraphMatcher"]
+
+
+class TimeRespectingGraphMatcher(GraphMatcher):
+    def __init__(self, G1, G2, temporal_attribute_name, delta):
+        """Initialize TimeRespectingGraphMatcher.
+
+        G1 and G2 should be nx.Graph or nx.MultiGraph instances.
+
+        Examples
+        --------
+        To create a TimeRespectingGraphMatcher which checks for
+        syntactic and semantic feasibility:
+
+        >>> from networkx.algorithms import isomorphism
+        >>> from datetime import timedelta
+        >>> G1 = nx.Graph(nx.path_graph(4, create_using=nx.Graph()))
+
+        >>> G2 = nx.Graph(nx.path_graph(4, create_using=nx.Graph()))
+
+        >>> GM = isomorphism.TimeRespectingGraphMatcher(G1, G2, "date", timedelta(days=1))
+        """
+        self.temporal_attribute_name = temporal_attribute_name
+        self.delta = delta
+        super().__init__(G1, G2)
+
+    def one_hop(self, Gx, Gx_node, neighbors):
+        """
+        Edges one hop out from a node in the mapping should be
+        time-respecting with respect to each other.
+        """
+        dates = []
+        for n in neighbors:
+            if isinstance(Gx, nx.Graph):  # Graph G[u][v] returns the data dictionary.
+                dates.append(Gx[Gx_node][n][self.temporal_attribute_name])
+            else:  # MultiGraph G[u][v] returns a dictionary of key -> data dictionary.
+                for edge in Gx[Gx_node][
+                    n
+                ].values():  # Iterates all edges between node pair.
+                    dates.append(edge[self.temporal_attribute_name])
+        if any(x is None for x in dates):
+            raise ValueError("Datetime not supplied for at least one edge.")
+        return not dates or max(dates) - min(dates) <= self.delta
+
+    def two_hop(self, Gx, core_x, Gx_node, neighbors):
+        """
+        Paths of length 2 from Gx_node should be time-respecting.
+        """
+        return all(
+            self.one_hop(Gx, v, [n for n in Gx[v] if n in core_x] + [Gx_node])
+            for v in neighbors
+        )
+
+    def semantic_feasibility(self, G1_node, G2_node):
+        """Returns True if adding (G1_node, G2_node) is semantically
+        feasible.
+
+        Any subclass which redefines semantic_feasibility() must
+        maintain the self.tests if needed, to keep the match() method
+        functional. Implementations should consider multigraphs.
+        """
+        neighbors = [n for n in self.G1[G1_node] if n in self.core_1]
+        if not self.one_hop(self.G1, G1_node, neighbors):  # Fail fast on first node.
+            return False
+        if not self.two_hop(self.G1, self.core_1, G1_node, neighbors):
+            return False
+        # Otherwise, this node is semantically feasible!
+        return True
+
+
+class TimeRespectingDiGraphMatcher(DiGraphMatcher):
+    def __init__(self, G1, G2, temporal_attribute_name, delta):
+        """Initialize TimeRespectingDiGraphMatcher.
+
+        G1 and G2 should be nx.DiGraph or nx.MultiDiGraph instances.
+
+        Examples
+        --------
+        To create a TimeRespectingDiGraphMatcher which checks for
+        syntactic and semantic feasibility:
+
+        >>> from networkx.algorithms import isomorphism
+        >>> from datetime import timedelta
+        >>> G1 = nx.DiGraph(nx.path_graph(4, create_using=nx.DiGraph()))
+
+        >>> G2 = nx.DiGraph(nx.path_graph(4, create_using=nx.DiGraph()))
+
+        >>> GM = isomorphism.TimeRespectingDiGraphMatcher(G1, G2, "date", timedelta(days=1))
+        """
+        self.temporal_attribute_name = temporal_attribute_name
+        self.delta = delta
+        super().__init__(G1, G2)
+
+    def get_pred_dates(self, Gx, Gx_node, core_x, pred):
+        """
+        Get the dates of edges from predecessors.
+        """
+        pred_dates = []
+        if isinstance(Gx, nx.DiGraph):  # Graph G[u][v] returns the data dictionary.
+            for n in pred:
+                pred_dates.append(Gx[n][Gx_node][self.temporal_attribute_name])
+        else:  # MultiGraph G[u][v] returns a dictionary of key -> data dictionary.
+            for n in pred:
+                for edge in Gx[n][
+                    Gx_node
+                ].values():  # Iterates all edge data between node pair.
+                    pred_dates.append(edge[self.temporal_attribute_name])
+        return pred_dates
+
+    def get_succ_dates(self, Gx, Gx_node, core_x, succ):
+        """
+        Get the dates of edges to successors.
+        """
+        succ_dates = []
+        if isinstance(Gx, nx.DiGraph):  # Graph G[u][v] returns the data dictionary.
+            for n in succ:
+                succ_dates.append(Gx[Gx_node][n][self.temporal_attribute_name])
+        else:  # MultiGraph G[u][v] returns a dictionary of key -> data dictionary.
+            for n in succ:
+                for edge in Gx[Gx_node][
+                    n
+                ].values():  # Iterates all edge data between node pair.
+                    succ_dates.append(edge[self.temporal_attribute_name])
+        return succ_dates
+
+    def one_hop(self, Gx, Gx_node, core_x, pred, succ):
+        """
+        The ego node.
+        """
+        pred_dates = self.get_pred_dates(Gx, Gx_node, core_x, pred)
+        succ_dates = self.get_succ_dates(Gx, Gx_node, core_x, succ)
+        return self.test_one(pred_dates, succ_dates) and self.test_two(
+            pred_dates, succ_dates
+        )
+
+    def two_hop_pred(self, Gx, Gx_node, core_x, pred):
+        """
+        The predecessors of the ego node.
+        """
+        return all(
+            self.one_hop(
+                Gx,
+                p,
+                core_x,
+                self.preds(Gx, core_x, p),
+                self.succs(Gx, core_x, p, Gx_node),
+            )
+            for p in pred
+        )
+
+    def two_hop_succ(self, Gx, Gx_node, core_x, succ):
+        """
+        The successors of the ego node.
+        """
+        return all(
+            self.one_hop(
+                Gx,
+                s,
+                core_x,
+                self.preds(Gx, core_x, s, Gx_node),
+                self.succs(Gx, core_x, s),
+            )
+            for s in succ
+        )
+
+    def preds(self, Gx, core_x, v, Gx_node=None):
+        pred = [n for n in Gx.predecessors(v) if n in core_x]
+        if Gx_node:
+            pred.append(Gx_node)
+        return pred
+
+    def succs(self, Gx, core_x, v, Gx_node=None):
+        succ = [n for n in Gx.successors(v) if n in core_x]
+        if Gx_node:
+            succ.append(Gx_node)
+        return succ
+
+    def test_one(self, pred_dates, succ_dates):
+        """
+        Edges one hop out from Gx_node in the mapping should be
+        time-respecting with respect to each other, regardless of
+        direction.
+        """
+        time_respecting = True
+        dates = pred_dates + succ_dates
+
+        if any(x is None for x in dates):
+            raise ValueError("Date or datetime not supplied for at least one edge.")
+
+        dates.sort()  # Small to large.
+        if 0 < len(dates) and not (dates[-1] - dates[0] <= self.delta):
+            time_respecting = False
+        return time_respecting
+
+    def test_two(self, pred_dates, succ_dates):
+        """
+        Edges from a dual Gx_node in the mapping should be ordered in
+        a time-respecting manner.
+        """
+        time_respecting = True
+        pred_dates.sort()
+        succ_dates.sort()
+        # First out before last in; negative of the necessary condition for time-respect.
+        if (
+            0 < len(succ_dates)
+            and 0 < len(pred_dates)
+            and succ_dates[0] < pred_dates[-1]
+        ):
+            time_respecting = False
+        return time_respecting
+
+    def semantic_feasibility(self, G1_node, G2_node):
+        """Returns True if adding (G1_node, G2_node) is semantically
+        feasible.
+
+        Any subclass which redefines semantic_feasibility() must
+        maintain the self.tests if needed, to keep the match() method
+        functional. Implementations should consider multigraphs.
+        """
+        pred, succ = (
+            [n for n in self.G1.predecessors(G1_node) if n in self.core_1],
+            [n for n in self.G1.successors(G1_node) if n in self.core_1],
+        )
+        if not self.one_hop(
+            self.G1, G1_node, self.core_1, pred, succ
+        ):  # Fail fast on first node.
+            return False
+        if not self.two_hop_pred(self.G1, G1_node, self.core_1, pred):
+            return False
+        if not self.two_hop_succ(self.G1, G1_node, self.core_1, succ):
+            return False
+        # Otherwise, this node is semantically feasible!
+        return True