diff --git "a/llmeval-env/lib/python3.10/site-packages/scipy/signal/_ltisys.py" "b/llmeval-env/lib/python3.10/site-packages/scipy/signal/_ltisys.py" new file mode 100644--- /dev/null +++ "b/llmeval-env/lib/python3.10/site-packages/scipy/signal/_ltisys.py" @@ -0,0 +1,3496 @@ +""" +ltisys -- a collection of classes and functions for modeling linear +time invariant systems. +""" +# +# Author: Travis Oliphant 2001 +# +# Feb 2010: Warren Weckesser +# Rewrote lsim2 and added impulse2. +# Apr 2011: Jeffrey Armstrong +# Added dlsim, dstep, dimpulse, cont2discrete +# Aug 2013: Juan Luis Cano +# Rewrote abcd_normalize. +# Jan 2015: Irvin Probst irvin DOT probst AT ensta-bretagne DOT fr +# Added pole placement +# Mar 2015: Clancy Rowley +# Rewrote lsim +# May 2015: Felix Berkenkamp +# Split lti class into subclasses +# Merged discrete systems and added dlti + +import warnings + +# np.linalg.qr fails on some tests with LinAlgError: zgeqrf returns -7 +# use scipy's qr until this is solved + +from scipy.linalg import qr as s_qr +from scipy import linalg +from scipy.interpolate import make_interp_spline +from ._filter_design import (tf2zpk, zpk2tf, normalize, freqs, freqz, freqs_zpk, + freqz_zpk) +from ._lti_conversion import (tf2ss, abcd_normalize, ss2tf, zpk2ss, ss2zpk, + cont2discrete, _atleast_2d_or_none) + +import numpy +import numpy as np +from numpy import (real, atleast_1d, squeeze, asarray, zeros, + dot, transpose, ones, linspace) +import copy + +__all__ = ['lti', 'dlti', 'TransferFunction', 'ZerosPolesGain', 'StateSpace', + 'lsim', 'impulse', 'step', 'bode', + 'freqresp', 'place_poles', 'dlsim', 'dstep', 'dimpulse', + 'dfreqresp', 'dbode'] + + +class LinearTimeInvariant: + def __new__(cls, *system, **kwargs): + """Create a new object, don't allow direct instances.""" + if cls is LinearTimeInvariant: + raise NotImplementedError('The LinearTimeInvariant class is not ' + 'meant to be used directly, use `lti` ' + 'or `dlti` instead.') + return super().__new__(cls) + + def __init__(self): + """ + Initialize the `lti` baseclass. + + The heavy lifting is done by the subclasses. + """ + super().__init__() + + self.inputs = None + self.outputs = None + self._dt = None + + @property + def dt(self): + """Return the sampling time of the system, `None` for `lti` systems.""" + return self._dt + + @property + def _dt_dict(self): + if self.dt is None: + return {} + else: + return {'dt': self.dt} + + @property + def zeros(self): + """Zeros of the system.""" + return self.to_zpk().zeros + + @property + def poles(self): + """Poles of the system.""" + return self.to_zpk().poles + + def _as_ss(self): + """Convert to `StateSpace` system, without copying. + + Returns + ------- + sys: StateSpace + The `StateSpace` system. If the class is already an instance of + `StateSpace` then this instance is returned. + """ + if isinstance(self, StateSpace): + return self + else: + return self.to_ss() + + def _as_zpk(self): + """Convert to `ZerosPolesGain` system, without copying. + + Returns + ------- + sys: ZerosPolesGain + The `ZerosPolesGain` system. If the class is already an instance of + `ZerosPolesGain` then this instance is returned. + """ + if isinstance(self, ZerosPolesGain): + return self + else: + return self.to_zpk() + + def _as_tf(self): + """Convert to `TransferFunction` system, without copying. + + Returns + ------- + sys: ZerosPolesGain + The `TransferFunction` system. If the class is already an instance of + `TransferFunction` then this instance is returned. + """ + if isinstance(self, TransferFunction): + return self + else: + return self.to_tf() + + +class lti(LinearTimeInvariant): + r""" + Continuous-time linear time invariant system base class. + + Parameters + ---------- + *system : arguments + The `lti` class can be instantiated with either 2, 3 or 4 arguments. + The following gives the number of arguments and the corresponding + continuous-time subclass that is created: + + * 2: `TransferFunction`: (numerator, denominator) + * 3: `ZerosPolesGain`: (zeros, poles, gain) + * 4: `StateSpace`: (A, B, C, D) + + Each argument can be an array or a sequence. + + See Also + -------- + ZerosPolesGain, StateSpace, TransferFunction, dlti + + Notes + ----- + `lti` instances do not exist directly. Instead, `lti` creates an instance + of one of its subclasses: `StateSpace`, `TransferFunction` or + `ZerosPolesGain`. + + If (numerator, denominator) is passed in for ``*system``, coefficients for + both the numerator and denominator should be specified in descending + exponent order (e.g., ``s^2 + 3s + 5`` would be represented as ``[1, 3, + 5]``). + + Changing the value of properties that are not directly part of the current + system representation (such as the `zeros` of a `StateSpace` system) is + very inefficient and may lead to numerical inaccuracies. It is better to + convert to the specific system representation first. For example, call + ``sys = sys.to_zpk()`` before accessing/changing the zeros, poles or gain. + + Examples + -------- + >>> from scipy import signal + + >>> signal.lti(1, 2, 3, 4) + StateSpaceContinuous( + array([[1]]), + array([[2]]), + array([[3]]), + array([[4]]), + dt: None + ) + + Construct the transfer function + :math:`H(s) = \frac{5(s - 1)(s - 2)}{(s - 3)(s - 4)}`: + + >>> signal.lti([1, 2], [3, 4], 5) + ZerosPolesGainContinuous( + array([1, 2]), + array([3, 4]), + 5, + dt: None + ) + + Construct the transfer function :math:`H(s) = \frac{3s + 4}{1s + 2}`: + + >>> signal.lti([3, 4], [1, 2]) + TransferFunctionContinuous( + array([3., 4.]), + array([1., 2.]), + dt: None + ) + + """ + def __new__(cls, *system): + """Create an instance of the appropriate subclass.""" + if cls is lti: + N = len(system) + if N == 2: + return TransferFunctionContinuous.__new__( + TransferFunctionContinuous, *system) + elif N == 3: + return ZerosPolesGainContinuous.__new__( + ZerosPolesGainContinuous, *system) + elif N == 4: + return StateSpaceContinuous.__new__(StateSpaceContinuous, + *system) + else: + raise ValueError("`system` needs to be an instance of `lti` " + "or have 2, 3 or 4 arguments.") + # __new__ was called from a subclass, let it call its own functions + return super().__new__(cls) + + def __init__(self, *system): + """ + Initialize the `lti` baseclass. + + The heavy lifting is done by the subclasses. + """ + super().__init__(*system) + + def impulse(self, X0=None, T=None, N=None): + """ + Return the impulse response of a continuous-time system. + See `impulse` for details. + """ + return impulse(self, X0=X0, T=T, N=N) + + def step(self, X0=None, T=None, N=None): + """ + Return the step response of a continuous-time system. + See `step` for details. + """ + return step(self, X0=X0, T=T, N=N) + + def output(self, U, T, X0=None): + """ + Return the response of a continuous-time system to input `U`. + See `lsim` for details. + """ + return lsim(self, U, T, X0=X0) + + def bode(self, w=None, n=100): + """ + Calculate Bode magnitude and phase data of a continuous-time system. + + Returns a 3-tuple containing arrays of frequencies [rad/s], magnitude + [dB] and phase [deg]. See `bode` for details. + + Examples + -------- + >>> from scipy import signal + >>> import matplotlib.pyplot as plt + + >>> sys = signal.TransferFunction([1], [1, 1]) + >>> w, mag, phase = sys.bode() + + >>> plt.figure() + >>> plt.semilogx(w, mag) # Bode magnitude plot + >>> plt.figure() + >>> plt.semilogx(w, phase) # Bode phase plot + >>> plt.show() + + """ + return bode(self, w=w, n=n) + + def freqresp(self, w=None, n=10000): + """ + Calculate the frequency response of a continuous-time system. + + Returns a 2-tuple containing arrays of frequencies [rad/s] and + complex magnitude. + See `freqresp` for details. + """ + return freqresp(self, w=w, n=n) + + def to_discrete(self, dt, method='zoh', alpha=None): + """Return a discretized version of the current system. + + Parameters: See `cont2discrete` for details. + + Returns + ------- + sys: instance of `dlti` + """ + raise NotImplementedError('to_discrete is not implemented for this ' + 'system class.') + + +class dlti(LinearTimeInvariant): + r""" + Discrete-time linear time invariant system base class. + + Parameters + ---------- + *system: arguments + The `dlti` class can be instantiated with either 2, 3 or 4 arguments. + The following gives the number of arguments and the corresponding + discrete-time subclass that is created: + + * 2: `TransferFunction`: (numerator, denominator) + * 3: `ZerosPolesGain`: (zeros, poles, gain) + * 4: `StateSpace`: (A, B, C, D) + + Each argument can be an array or a sequence. + dt: float, optional + Sampling time [s] of the discrete-time systems. Defaults to ``True`` + (unspecified sampling time). Must be specified as a keyword argument, + for example, ``dt=0.1``. + + See Also + -------- + ZerosPolesGain, StateSpace, TransferFunction, lti + + Notes + ----- + `dlti` instances do not exist directly. Instead, `dlti` creates an instance + of one of its subclasses: `StateSpace`, `TransferFunction` or + `ZerosPolesGain`. + + Changing the value of properties that are not directly part of the current + system representation (such as the `zeros` of a `StateSpace` system) is + very inefficient and may lead to numerical inaccuracies. It is better to + convert to the specific system representation first. For example, call + ``sys = sys.to_zpk()`` before accessing/changing the zeros, poles or gain. + + If (numerator, denominator) is passed in for ``*system``, coefficients for + both the numerator and denominator should be specified in descending + exponent order (e.g., ``z^2 + 3z + 5`` would be represented as ``[1, 3, + 5]``). + + .. versionadded:: 0.18.0 + + Examples + -------- + >>> from scipy import signal + + >>> signal.dlti(1, 2, 3, 4) + StateSpaceDiscrete( + array([[1]]), + array([[2]]), + array([[3]]), + array([[4]]), + dt: True + ) + + >>> signal.dlti(1, 2, 3, 4, dt=0.1) + StateSpaceDiscrete( + array([[1]]), + array([[2]]), + array([[3]]), + array([[4]]), + dt: 0.1 + ) + + Construct the transfer function + :math:`H(z) = \frac{5(z - 1)(z - 2)}{(z - 3)(z - 4)}` with a sampling time + of 0.1 seconds: + + >>> signal.dlti([1, 2], [3, 4], 5, dt=0.1) + ZerosPolesGainDiscrete( + array([1, 2]), + array([3, 4]), + 5, + dt: 0.1 + ) + + Construct the transfer function :math:`H(z) = \frac{3z + 4}{1z + 2}` with + a sampling time of 0.1 seconds: + + >>> signal.dlti([3, 4], [1, 2], dt=0.1) + TransferFunctionDiscrete( + array([3., 4.]), + array([1., 2.]), + dt: 0.1 + ) + + """ + def __new__(cls, *system, **kwargs): + """Create an instance of the appropriate subclass.""" + if cls is dlti: + N = len(system) + if N == 2: + return TransferFunctionDiscrete.__new__( + TransferFunctionDiscrete, *system, **kwargs) + elif N == 3: + return ZerosPolesGainDiscrete.__new__(ZerosPolesGainDiscrete, + *system, **kwargs) + elif N == 4: + return StateSpaceDiscrete.__new__(StateSpaceDiscrete, *system, + **kwargs) + else: + raise ValueError("`system` needs to be an instance of `dlti` " + "or have 2, 3 or 4 arguments.") + # __new__ was called from a subclass, let it call its own functions + return super().__new__(cls) + + def __init__(self, *system, **kwargs): + """ + Initialize the `lti` baseclass. + + The heavy lifting is done by the subclasses. + """ + dt = kwargs.pop('dt', True) + super().__init__(*system, **kwargs) + + self.dt = dt + + @property + def dt(self): + """Return the sampling time of the system.""" + return self._dt + + @dt.setter + def dt(self, dt): + self._dt = dt + + def impulse(self, x0=None, t=None, n=None): + """ + Return the impulse response of the discrete-time `dlti` system. + See `dimpulse` for details. + """ + return dimpulse(self, x0=x0, t=t, n=n) + + def step(self, x0=None, t=None, n=None): + """ + Return the step response of the discrete-time `dlti` system. + See `dstep` for details. + """ + return dstep(self, x0=x0, t=t, n=n) + + def output(self, u, t, x0=None): + """ + Return the response of the discrete-time system to input `u`. + See `dlsim` for details. + """ + return dlsim(self, u, t, x0=x0) + + def bode(self, w=None, n=100): + r""" + Calculate Bode magnitude and phase data of a discrete-time system. + + Returns a 3-tuple containing arrays of frequencies [rad/s], magnitude + [dB] and phase [deg]. See `dbode` for details. + + Examples + -------- + >>> from scipy import signal + >>> import matplotlib.pyplot as plt + + Construct the transfer function :math:`H(z) = \frac{1}{z^2 + 2z + 3}` + with sampling time 0.5s: + + >>> sys = signal.TransferFunction([1], [1, 2, 3], dt=0.5) + + Equivalent: signal.dbode(sys) + + >>> w, mag, phase = sys.bode() + + >>> plt.figure() + >>> plt.semilogx(w, mag) # Bode magnitude plot + >>> plt.figure() + >>> plt.semilogx(w, phase) # Bode phase plot + >>> plt.show() + + """ + return dbode(self, w=w, n=n) + + def freqresp(self, w=None, n=10000, whole=False): + """ + Calculate the frequency response of a discrete-time system. + + Returns a 2-tuple containing arrays of frequencies [rad/s] and + complex magnitude. + See `dfreqresp` for details. + + """ + return dfreqresp(self, w=w, n=n, whole=whole) + + +class TransferFunction(LinearTimeInvariant): + r"""Linear Time Invariant system class in transfer function form. + + Represents the system as the continuous-time transfer function + :math:`H(s)=\sum_{i=0}^N b[N-i] s^i / \sum_{j=0}^M a[M-j] s^j` or the + discrete-time transfer function + :math:`H(z)=\sum_{i=0}^N b[N-i] z^i / \sum_{j=0}^M a[M-j] z^j`, where + :math:`b` are elements of the numerator `num`, :math:`a` are elements of + the denominator `den`, and ``N == len(b) - 1``, ``M == len(a) - 1``. + `TransferFunction` systems inherit additional + functionality from the `lti`, respectively the `dlti` classes, depending on + which system representation is used. + + Parameters + ---------- + *system: arguments + The `TransferFunction` class can be instantiated with 1 or 2 + arguments. The following gives the number of input arguments and their + interpretation: + + * 1: `lti` or `dlti` system: (`StateSpace`, `TransferFunction` or + `ZerosPolesGain`) + * 2: array_like: (numerator, denominator) + dt: float, optional + Sampling time [s] of the discrete-time systems. Defaults to `None` + (continuous-time). Must be specified as a keyword argument, for + example, ``dt=0.1``. + + See Also + -------- + ZerosPolesGain, StateSpace, lti, dlti + tf2ss, tf2zpk, tf2sos + + Notes + ----- + Changing the value of properties that are not part of the + `TransferFunction` system representation (such as the `A`, `B`, `C`, `D` + state-space matrices) is very inefficient and may lead to numerical + inaccuracies. It is better to convert to the specific system + representation first. For example, call ``sys = sys.to_ss()`` before + accessing/changing the A, B, C, D system matrices. + + If (numerator, denominator) is passed in for ``*system``, coefficients + for both the numerator and denominator should be specified in descending + exponent order (e.g. ``s^2 + 3s + 5`` or ``z^2 + 3z + 5`` would be + represented as ``[1, 3, 5]``) + + Examples + -------- + Construct the transfer function + :math:`H(s) = \frac{s^2 + 3s + 3}{s^2 + 2s + 1}`: + + >>> from scipy import signal + + >>> num = [1, 3, 3] + >>> den = [1, 2, 1] + + >>> signal.TransferFunction(num, den) + TransferFunctionContinuous( + array([1., 3., 3.]), + array([1., 2., 1.]), + dt: None + ) + + Construct the transfer function + :math:`H(z) = \frac{z^2 + 3z + 3}{z^2 + 2z + 1}` with a sampling time of + 0.1 seconds: + + >>> signal.TransferFunction(num, den, dt=0.1) + TransferFunctionDiscrete( + array([1., 3., 3.]), + array([1., 2., 1.]), + dt: 0.1 + ) + + """ + def __new__(cls, *system, **kwargs): + """Handle object conversion if input is an instance of lti.""" + if len(system) == 1 and isinstance(system[0], LinearTimeInvariant): + return system[0].to_tf() + + # Choose whether to inherit from `lti` or from `dlti` + if cls is TransferFunction: + if kwargs.get('dt') is None: + return TransferFunctionContinuous.__new__( + TransferFunctionContinuous, + *system, + **kwargs) + else: + return TransferFunctionDiscrete.__new__( + TransferFunctionDiscrete, + *system, + **kwargs) + + # No special conversion needed + return super().__new__(cls) + + def __init__(self, *system, **kwargs): + """Initialize the state space LTI system.""" + # Conversion of lti instances is handled in __new__ + if isinstance(system[0], LinearTimeInvariant): + return + + # Remove system arguments, not needed by parents anymore + super().__init__(**kwargs) + + self._num = None + self._den = None + + self.num, self.den = normalize(*system) + + def __repr__(self): + """Return representation of the system's transfer function""" + return '{}(\n{},\n{},\ndt: {}\n)'.format( + self.__class__.__name__, + repr(self.num), + repr(self.den), + repr(self.dt), + ) + + @property + def num(self): + """Numerator of the `TransferFunction` system.""" + return self._num + + @num.setter + def num(self, num): + self._num = atleast_1d(num) + + # Update dimensions + if len(self.num.shape) > 1: + self.outputs, self.inputs = self.num.shape + else: + self.outputs = 1 + self.inputs = 1 + + @property + def den(self): + """Denominator of the `TransferFunction` system.""" + return self._den + + @den.setter + def den(self, den): + self._den = atleast_1d(den) + + def _copy(self, system): + """ + Copy the parameters of another `TransferFunction` object + + Parameters + ---------- + system : `TransferFunction` + The `StateSpace` system that is to be copied + + """ + self.num = system.num + self.den = system.den + + def to_tf(self): + """ + Return a copy of the current `TransferFunction` system. + + Returns + ------- + sys : instance of `TransferFunction` + The current system (copy) + + """ + return copy.deepcopy(self) + + def to_zpk(self): + """ + Convert system representation to `ZerosPolesGain`. + + Returns + ------- + sys : instance of `ZerosPolesGain` + Zeros, poles, gain representation of the current system + + """ + return ZerosPolesGain(*tf2zpk(self.num, self.den), + **self._dt_dict) + + def to_ss(self): + """ + Convert system representation to `StateSpace`. + + Returns + ------- + sys : instance of `StateSpace` + State space model of the current system + + """ + return StateSpace(*tf2ss(self.num, self.den), + **self._dt_dict) + + @staticmethod + def _z_to_zinv(num, den): + """Change a transfer function from the variable `z` to `z**-1`. + + Parameters + ---------- + num, den: 1d array_like + Sequences representing the coefficients of the numerator and + denominator polynomials, in order of descending degree of 'z'. + That is, ``5z**2 + 3z + 2`` is presented as ``[5, 3, 2]``. + + Returns + ------- + num, den: 1d array_like + Sequences representing the coefficients of the numerator and + denominator polynomials, in order of ascending degree of 'z**-1'. + That is, ``5 + 3 z**-1 + 2 z**-2`` is presented as ``[5, 3, 2]``. + """ + diff = len(num) - len(den) + if diff > 0: + den = np.hstack((np.zeros(diff), den)) + elif diff < 0: + num = np.hstack((np.zeros(-diff), num)) + return num, den + + @staticmethod + def _zinv_to_z(num, den): + """Change a transfer function from the variable `z` to `z**-1`. + + Parameters + ---------- + num, den: 1d array_like + Sequences representing the coefficients of the numerator and + denominator polynomials, in order of ascending degree of 'z**-1'. + That is, ``5 + 3 z**-1 + 2 z**-2`` is presented as ``[5, 3, 2]``. + + Returns + ------- + num, den: 1d array_like + Sequences representing the coefficients of the numerator and + denominator polynomials, in order of descending degree of 'z'. + That is, ``5z**2 + 3z + 2`` is presented as ``[5, 3, 2]``. + """ + diff = len(num) - len(den) + if diff > 0: + den = np.hstack((den, np.zeros(diff))) + elif diff < 0: + num = np.hstack((num, np.zeros(-diff))) + return num, den + + +class TransferFunctionContinuous(TransferFunction, lti): + r""" + Continuous-time Linear Time Invariant system in transfer function form. + + Represents the system as the transfer function + :math:`H(s)=\sum_{i=0}^N b[N-i] s^i / \sum_{j=0}^M a[M-j] s^j`, where + :math:`b` are elements of the numerator `num`, :math:`a` are elements of + the denominator `den`, and ``N == len(b) - 1``, ``M == len(a) - 1``. + Continuous-time `TransferFunction` systems inherit additional + functionality from the `lti` class. + + Parameters + ---------- + *system: arguments + The `TransferFunction` class can be instantiated with 1 or 2 + arguments. The following gives the number of input arguments and their + interpretation: + + * 1: `lti` system: (`StateSpace`, `TransferFunction` or + `ZerosPolesGain`) + * 2: array_like: (numerator, denominator) + + See Also + -------- + ZerosPolesGain, StateSpace, lti + tf2ss, tf2zpk, tf2sos + + Notes + ----- + Changing the value of properties that are not part of the + `TransferFunction` system representation (such as the `A`, `B`, `C`, `D` + state-space matrices) is very inefficient and may lead to numerical + inaccuracies. It is better to convert to the specific system + representation first. For example, call ``sys = sys.to_ss()`` before + accessing/changing the A, B, C, D system matrices. + + If (numerator, denominator) is passed in for ``*system``, coefficients + for both the numerator and denominator should be specified in descending + exponent order (e.g. ``s^2 + 3s + 5`` would be represented as + ``[1, 3, 5]``) + + Examples + -------- + Construct the transfer function + :math:`H(s) = \frac{s^2 + 3s + 3}{s^2 + 2s + 1}`: + + >>> from scipy import signal + + >>> num = [1, 3, 3] + >>> den = [1, 2, 1] + + >>> signal.TransferFunction(num, den) + TransferFunctionContinuous( + array([ 1., 3., 3.]), + array([ 1., 2., 1.]), + dt: None + ) + + """ + + def to_discrete(self, dt, method='zoh', alpha=None): + """ + Returns the discretized `TransferFunction` system. + + Parameters: See `cont2discrete` for details. + + Returns + ------- + sys: instance of `dlti` and `StateSpace` + """ + return TransferFunction(*cont2discrete((self.num, self.den), + dt, + method=method, + alpha=alpha)[:-1], + dt=dt) + + +class TransferFunctionDiscrete(TransferFunction, dlti): + r""" + Discrete-time Linear Time Invariant system in transfer function form. + + Represents the system as the transfer function + :math:`H(z)=\sum_{i=0}^N b[N-i] z^i / \sum_{j=0}^M a[M-j] z^j`, where + :math:`b` are elements of the numerator `num`, :math:`a` are elements of + the denominator `den`, and ``N == len(b) - 1``, ``M == len(a) - 1``. + Discrete-time `TransferFunction` systems inherit additional functionality + from the `dlti` class. + + Parameters + ---------- + *system: arguments + The `TransferFunction` class can be instantiated with 1 or 2 + arguments. The following gives the number of input arguments and their + interpretation: + + * 1: `dlti` system: (`StateSpace`, `TransferFunction` or + `ZerosPolesGain`) + * 2: array_like: (numerator, denominator) + dt: float, optional + Sampling time [s] of the discrete-time systems. Defaults to `True` + (unspecified sampling time). Must be specified as a keyword argument, + for example, ``dt=0.1``. + + See Also + -------- + ZerosPolesGain, StateSpace, dlti + tf2ss, tf2zpk, tf2sos + + Notes + ----- + Changing the value of properties that are not part of the + `TransferFunction` system representation (such as the `A`, `B`, `C`, `D` + state-space matrices) is very inefficient and may lead to numerical + inaccuracies. + + If (numerator, denominator) is passed in for ``*system``, coefficients + for both the numerator and denominator should be specified in descending + exponent order (e.g., ``z^2 + 3z + 5`` would be represented as + ``[1, 3, 5]``). + + Examples + -------- + Construct the transfer function + :math:`H(z) = \frac{z^2 + 3z + 3}{z^2 + 2z + 1}` with a sampling time of + 0.5 seconds: + + >>> from scipy import signal + + >>> num = [1, 3, 3] + >>> den = [1, 2, 1] + + >>> signal.TransferFunction(num, den, dt=0.5) + TransferFunctionDiscrete( + array([ 1., 3., 3.]), + array([ 1., 2., 1.]), + dt: 0.5 + ) + + """ + pass + + +class ZerosPolesGain(LinearTimeInvariant): + r""" + Linear Time Invariant system class in zeros, poles, gain form. + + Represents the system as the continuous- or discrete-time transfer function + :math:`H(s)=k \prod_i (s - z[i]) / \prod_j (s - p[j])`, where :math:`k` is + the `gain`, :math:`z` are the `zeros` and :math:`p` are the `poles`. + `ZerosPolesGain` systems inherit additional functionality from the `lti`, + respectively the `dlti` classes, depending on which system representation + is used. + + Parameters + ---------- + *system : arguments + The `ZerosPolesGain` class can be instantiated with 1 or 3 + arguments. The following gives the number of input arguments and their + interpretation: + + * 1: `lti` or `dlti` system: (`StateSpace`, `TransferFunction` or + `ZerosPolesGain`) + * 3: array_like: (zeros, poles, gain) + dt: float, optional + Sampling time [s] of the discrete-time systems. Defaults to `None` + (continuous-time). Must be specified as a keyword argument, for + example, ``dt=0.1``. + + + See Also + -------- + TransferFunction, StateSpace, lti, dlti + zpk2ss, zpk2tf, zpk2sos + + Notes + ----- + Changing the value of properties that are not part of the + `ZerosPolesGain` system representation (such as the `A`, `B`, `C`, `D` + state-space matrices) is very inefficient and may lead to numerical + inaccuracies. It is better to convert to the specific system + representation first. For example, call ``sys = sys.to_ss()`` before + accessing/changing the A, B, C, D system matrices. + + Examples + -------- + Construct the transfer function + :math:`H(s) = \frac{5(s - 1)(s - 2)}{(s - 3)(s - 4)}`: + + >>> from scipy import signal + + >>> signal.ZerosPolesGain([1, 2], [3, 4], 5) + ZerosPolesGainContinuous( + array([1, 2]), + array([3, 4]), + 5, + dt: None + ) + + Construct the transfer function + :math:`H(z) = \frac{5(z - 1)(z - 2)}{(z - 3)(z - 4)}` with a sampling time + of 0.1 seconds: + + >>> signal.ZerosPolesGain([1, 2], [3, 4], 5, dt=0.1) + ZerosPolesGainDiscrete( + array([1, 2]), + array([3, 4]), + 5, + dt: 0.1 + ) + + """ + def __new__(cls, *system, **kwargs): + """Handle object conversion if input is an instance of `lti`""" + if len(system) == 1 and isinstance(system[0], LinearTimeInvariant): + return system[0].to_zpk() + + # Choose whether to inherit from `lti` or from `dlti` + if cls is ZerosPolesGain: + if kwargs.get('dt') is None: + return ZerosPolesGainContinuous.__new__( + ZerosPolesGainContinuous, + *system, + **kwargs) + else: + return ZerosPolesGainDiscrete.__new__( + ZerosPolesGainDiscrete, + *system, + **kwargs + ) + + # No special conversion needed + return super().__new__(cls) + + def __init__(self, *system, **kwargs): + """Initialize the zeros, poles, gain system.""" + # Conversion of lti instances is handled in __new__ + if isinstance(system[0], LinearTimeInvariant): + return + + super().__init__(**kwargs) + + self._zeros = None + self._poles = None + self._gain = None + + self.zeros, self.poles, self.gain = system + + def __repr__(self): + """Return representation of the `ZerosPolesGain` system.""" + return '{}(\n{},\n{},\n{},\ndt: {}\n)'.format( + self.__class__.__name__, + repr(self.zeros), + repr(self.poles), + repr(self.gain), + repr(self.dt), + ) + + @property + def zeros(self): + """Zeros of the `ZerosPolesGain` system.""" + return self._zeros + + @zeros.setter + def zeros(self, zeros): + self._zeros = atleast_1d(zeros) + + # Update dimensions + if len(self.zeros.shape) > 1: + self.outputs, self.inputs = self.zeros.shape + else: + self.outputs = 1 + self.inputs = 1 + + @property + def poles(self): + """Poles of the `ZerosPolesGain` system.""" + return self._poles + + @poles.setter + def poles(self, poles): + self._poles = atleast_1d(poles) + + @property + def gain(self): + """Gain of the `ZerosPolesGain` system.""" + return self._gain + + @gain.setter + def gain(self, gain): + self._gain = gain + + def _copy(self, system): + """ + Copy the parameters of another `ZerosPolesGain` system. + + Parameters + ---------- + system : instance of `ZerosPolesGain` + The zeros, poles gain system that is to be copied + + """ + self.poles = system.poles + self.zeros = system.zeros + self.gain = system.gain + + def to_tf(self): + """ + Convert system representation to `TransferFunction`. + + Returns + ------- + sys : instance of `TransferFunction` + Transfer function of the current system + + """ + return TransferFunction(*zpk2tf(self.zeros, self.poles, self.gain), + **self._dt_dict) + + def to_zpk(self): + """ + Return a copy of the current 'ZerosPolesGain' system. + + Returns + ------- + sys : instance of `ZerosPolesGain` + The current system (copy) + + """ + return copy.deepcopy(self) + + def to_ss(self): + """ + Convert system representation to `StateSpace`. + + Returns + ------- + sys : instance of `StateSpace` + State space model of the current system + + """ + return StateSpace(*zpk2ss(self.zeros, self.poles, self.gain), + **self._dt_dict) + + +class ZerosPolesGainContinuous(ZerosPolesGain, lti): + r""" + Continuous-time Linear Time Invariant system in zeros, poles, gain form. + + Represents the system as the continuous time transfer function + :math:`H(s)=k \prod_i (s - z[i]) / \prod_j (s - p[j])`, where :math:`k` is + the `gain`, :math:`z` are the `zeros` and :math:`p` are the `poles`. + Continuous-time `ZerosPolesGain` systems inherit additional functionality + from the `lti` class. + + Parameters + ---------- + *system : arguments + The `ZerosPolesGain` class can be instantiated with 1 or 3 + arguments. The following gives the number of input arguments and their + interpretation: + + * 1: `lti` system: (`StateSpace`, `TransferFunction` or + `ZerosPolesGain`) + * 3: array_like: (zeros, poles, gain) + + See Also + -------- + TransferFunction, StateSpace, lti + zpk2ss, zpk2tf, zpk2sos + + Notes + ----- + Changing the value of properties that are not part of the + `ZerosPolesGain` system representation (such as the `A`, `B`, `C`, `D` + state-space matrices) is very inefficient and may lead to numerical + inaccuracies. It is better to convert to the specific system + representation first. For example, call ``sys = sys.to_ss()`` before + accessing/changing the A, B, C, D system matrices. + + Examples + -------- + Construct the transfer function + :math:`H(s)=\frac{5(s - 1)(s - 2)}{(s - 3)(s - 4)}`: + + >>> from scipy import signal + + >>> signal.ZerosPolesGain([1, 2], [3, 4], 5) + ZerosPolesGainContinuous( + array([1, 2]), + array([3, 4]), + 5, + dt: None + ) + + """ + + def to_discrete(self, dt, method='zoh', alpha=None): + """ + Returns the discretized `ZerosPolesGain` system. + + Parameters: See `cont2discrete` for details. + + Returns + ------- + sys: instance of `dlti` and `ZerosPolesGain` + """ + return ZerosPolesGain( + *cont2discrete((self.zeros, self.poles, self.gain), + dt, + method=method, + alpha=alpha)[:-1], + dt=dt) + + +class ZerosPolesGainDiscrete(ZerosPolesGain, dlti): + r""" + Discrete-time Linear Time Invariant system in zeros, poles, gain form. + + Represents the system as the discrete-time transfer function + :math:`H(z)=k \prod_i (z - q[i]) / \prod_j (z - p[j])`, where :math:`k` is + the `gain`, :math:`q` are the `zeros` and :math:`p` are the `poles`. + Discrete-time `ZerosPolesGain` systems inherit additional functionality + from the `dlti` class. + + Parameters + ---------- + *system : arguments + The `ZerosPolesGain` class can be instantiated with 1 or 3 + arguments. The following gives the number of input arguments and their + interpretation: + + * 1: `dlti` system: (`StateSpace`, `TransferFunction` or + `ZerosPolesGain`) + * 3: array_like: (zeros, poles, gain) + dt: float, optional + Sampling time [s] of the discrete-time systems. Defaults to `True` + (unspecified sampling time). Must be specified as a keyword argument, + for example, ``dt=0.1``. + + See Also + -------- + TransferFunction, StateSpace, dlti + zpk2ss, zpk2tf, zpk2sos + + Notes + ----- + Changing the value of properties that are not part of the + `ZerosPolesGain` system representation (such as the `A`, `B`, `C`, `D` + state-space matrices) is very inefficient and may lead to numerical + inaccuracies. It is better to convert to the specific system + representation first. For example, call ``sys = sys.to_ss()`` before + accessing/changing the A, B, C, D system matrices. + + Examples + -------- + Construct the transfer function + :math:`H(s) = \frac{5(s - 1)(s - 2)}{(s - 3)(s - 4)}`: + + >>> from scipy import signal + + >>> signal.ZerosPolesGain([1, 2], [3, 4], 5) + ZerosPolesGainContinuous( + array([1, 2]), + array([3, 4]), + 5, + dt: None + ) + + Construct the transfer function + :math:`H(z) = \frac{5(z - 1)(z - 2)}{(z - 3)(z - 4)}` with a sampling time + of 0.1 seconds: + + >>> signal.ZerosPolesGain([1, 2], [3, 4], 5, dt=0.1) + ZerosPolesGainDiscrete( + array([1, 2]), + array([3, 4]), + 5, + dt: 0.1 + ) + + """ + pass + + +class StateSpace(LinearTimeInvariant): + r""" + Linear Time Invariant system in state-space form. + + Represents the system as the continuous-time, first order differential + equation :math:`\dot{x} = A x + B u` or the discrete-time difference + equation :math:`x[k+1] = A x[k] + B u[k]`. `StateSpace` systems + inherit additional functionality from the `lti`, respectively the `dlti` + classes, depending on which system representation is used. + + Parameters + ---------- + *system: arguments + The `StateSpace` class can be instantiated with 1 or 4 arguments. + The following gives the number of input arguments and their + interpretation: + + * 1: `lti` or `dlti` system: (`StateSpace`, `TransferFunction` or + `ZerosPolesGain`) + * 4: array_like: (A, B, C, D) + dt: float, optional + Sampling time [s] of the discrete-time systems. Defaults to `None` + (continuous-time). Must be specified as a keyword argument, for + example, ``dt=0.1``. + + See Also + -------- + TransferFunction, ZerosPolesGain, lti, dlti + ss2zpk, ss2tf, zpk2sos + + Notes + ----- + Changing the value of properties that are not part of the + `StateSpace` system representation (such as `zeros` or `poles`) is very + inefficient and may lead to numerical inaccuracies. It is better to + convert to the specific system representation first. For example, call + ``sys = sys.to_zpk()`` before accessing/changing the zeros, poles or gain. + + Examples + -------- + >>> from scipy import signal + >>> import numpy as np + >>> a = np.array([[0, 1], [0, 0]]) + >>> b = np.array([[0], [1]]) + >>> c = np.array([[1, 0]]) + >>> d = np.array([[0]]) + + >>> sys = signal.StateSpace(a, b, c, d) + >>> print(sys) + StateSpaceContinuous( + array([[0, 1], + [0, 0]]), + array([[0], + [1]]), + array([[1, 0]]), + array([[0]]), + dt: None + ) + + >>> sys.to_discrete(0.1) + StateSpaceDiscrete( + array([[1. , 0.1], + [0. , 1. ]]), + array([[0.005], + [0.1 ]]), + array([[1, 0]]), + array([[0]]), + dt: 0.1 + ) + + >>> a = np.array([[1, 0.1], [0, 1]]) + >>> b = np.array([[0.005], [0.1]]) + + >>> signal.StateSpace(a, b, c, d, dt=0.1) + StateSpaceDiscrete( + array([[1. , 0.1], + [0. , 1. ]]), + array([[0.005], + [0.1 ]]), + array([[1, 0]]), + array([[0]]), + dt: 0.1 + ) + + """ + + # Override NumPy binary operations and ufuncs + __array_priority__ = 100.0 + __array_ufunc__ = None + + def __new__(cls, *system, **kwargs): + """Create new StateSpace object and settle inheritance.""" + # Handle object conversion if input is an instance of `lti` + if len(system) == 1 and isinstance(system[0], LinearTimeInvariant): + return system[0].to_ss() + + # Choose whether to inherit from `lti` or from `dlti` + if cls is StateSpace: + if kwargs.get('dt') is None: + return StateSpaceContinuous.__new__(StateSpaceContinuous, + *system, **kwargs) + else: + return StateSpaceDiscrete.__new__(StateSpaceDiscrete, + *system, **kwargs) + + # No special conversion needed + return super().__new__(cls) + + def __init__(self, *system, **kwargs): + """Initialize the state space lti/dlti system.""" + # Conversion of lti instances is handled in __new__ + if isinstance(system[0], LinearTimeInvariant): + return + + # Remove system arguments, not needed by parents anymore + super().__init__(**kwargs) + + self._A = None + self._B = None + self._C = None + self._D = None + + self.A, self.B, self.C, self.D = abcd_normalize(*system) + + def __repr__(self): + """Return representation of the `StateSpace` system.""" + return '{}(\n{},\n{},\n{},\n{},\ndt: {}\n)'.format( + self.__class__.__name__, + repr(self.A), + repr(self.B), + repr(self.C), + repr(self.D), + repr(self.dt), + ) + + def _check_binop_other(self, other): + return isinstance(other, (StateSpace, np.ndarray, float, complex, + np.number, int)) + + def __mul__(self, other): + """ + Post-multiply another system or a scalar + + Handles multiplication of systems in the sense of a frequency domain + multiplication. That means, given two systems E1(s) and E2(s), their + multiplication, H(s) = E1(s) * E2(s), means that applying H(s) to U(s) + is equivalent to first applying E2(s), and then E1(s). + + Notes + ----- + For SISO systems the order of system application does not matter. + However, for MIMO systems, where the two systems are matrices, the + order above ensures standard Matrix multiplication rules apply. + """ + if not self._check_binop_other(other): + return NotImplemented + + if isinstance(other, StateSpace): + # Disallow mix of discrete and continuous systems. + if type(other) is not type(self): + return NotImplemented + + if self.dt != other.dt: + raise TypeError('Cannot multiply systems with different `dt`.') + + n1 = self.A.shape[0] + n2 = other.A.shape[0] + + # Interconnection of systems + # x1' = A1 x1 + B1 u1 + # y1 = C1 x1 + D1 u1 + # x2' = A2 x2 + B2 y1 + # y2 = C2 x2 + D2 y1 + # + # Plugging in with u1 = y2 yields + # [x1'] [A1 B1*C2 ] [x1] [B1*D2] + # [x2'] = [0 A2 ] [x2] + [B2 ] u2 + # [x1] + # y2 = [C1 D1*C2] [x2] + D1*D2 u2 + a = np.vstack((np.hstack((self.A, np.dot(self.B, other.C))), + np.hstack((zeros((n2, n1)), other.A)))) + b = np.vstack((np.dot(self.B, other.D), other.B)) + c = np.hstack((self.C, np.dot(self.D, other.C))) + d = np.dot(self.D, other.D) + else: + # Assume that other is a scalar / matrix + # For post multiplication the input gets scaled + a = self.A + b = np.dot(self.B, other) + c = self.C + d = np.dot(self.D, other) + + common_dtype = np.result_type(a.dtype, b.dtype, c.dtype, d.dtype) + return StateSpace(np.asarray(a, dtype=common_dtype), + np.asarray(b, dtype=common_dtype), + np.asarray(c, dtype=common_dtype), + np.asarray(d, dtype=common_dtype), + **self._dt_dict) + + def __rmul__(self, other): + """Pre-multiply a scalar or matrix (but not StateSpace)""" + if not self._check_binop_other(other) or isinstance(other, StateSpace): + return NotImplemented + + # For pre-multiplication only the output gets scaled + a = self.A + b = self.B + c = np.dot(other, self.C) + d = np.dot(other, self.D) + + common_dtype = np.result_type(a.dtype, b.dtype, c.dtype, d.dtype) + return StateSpace(np.asarray(a, dtype=common_dtype), + np.asarray(b, dtype=common_dtype), + np.asarray(c, dtype=common_dtype), + np.asarray(d, dtype=common_dtype), + **self._dt_dict) + + def __neg__(self): + """Negate the system (equivalent to pre-multiplying by -1).""" + return StateSpace(self.A, self.B, -self.C, -self.D, **self._dt_dict) + + def __add__(self, other): + """ + Adds two systems in the sense of frequency domain addition. + """ + if not self._check_binop_other(other): + return NotImplemented + + if isinstance(other, StateSpace): + # Disallow mix of discrete and continuous systems. + if type(other) is not type(self): + raise TypeError(f'Cannot add {type(self)} and {type(other)}') + + if self.dt != other.dt: + raise TypeError('Cannot add systems with different `dt`.') + # Interconnection of systems + # x1' = A1 x1 + B1 u + # y1 = C1 x1 + D1 u + # x2' = A2 x2 + B2 u + # y2 = C2 x2 + D2 u + # y = y1 + y2 + # + # Plugging in yields + # [x1'] [A1 0 ] [x1] [B1] + # [x2'] = [0 A2] [x2] + [B2] u + # [x1] + # y = [C1 C2] [x2] + [D1 + D2] u + a = linalg.block_diag(self.A, other.A) + b = np.vstack((self.B, other.B)) + c = np.hstack((self.C, other.C)) + d = self.D + other.D + else: + other = np.atleast_2d(other) + if self.D.shape == other.shape: + # A scalar/matrix is really just a static system (A=0, B=0, C=0) + a = self.A + b = self.B + c = self.C + d = self.D + other + else: + raise ValueError("Cannot add systems with incompatible " + f"dimensions ({self.D.shape} and {other.shape})") + + common_dtype = np.result_type(a.dtype, b.dtype, c.dtype, d.dtype) + return StateSpace(np.asarray(a, dtype=common_dtype), + np.asarray(b, dtype=common_dtype), + np.asarray(c, dtype=common_dtype), + np.asarray(d, dtype=common_dtype), + **self._dt_dict) + + def __sub__(self, other): + if not self._check_binop_other(other): + return NotImplemented + + return self.__add__(-other) + + def __radd__(self, other): + if not self._check_binop_other(other): + return NotImplemented + + return self.__add__(other) + + def __rsub__(self, other): + if not self._check_binop_other(other): + return NotImplemented + + return (-self).__add__(other) + + def __truediv__(self, other): + """ + Divide by a scalar + """ + # Division by non-StateSpace scalars + if not self._check_binop_other(other) or isinstance(other, StateSpace): + return NotImplemented + + if isinstance(other, np.ndarray) and other.ndim > 0: + # It's ambiguous what this means, so disallow it + raise ValueError("Cannot divide StateSpace by non-scalar numpy arrays") + + return self.__mul__(1/other) + + @property + def A(self): + """State matrix of the `StateSpace` system.""" + return self._A + + @A.setter + def A(self, A): + self._A = _atleast_2d_or_none(A) + + @property + def B(self): + """Input matrix of the `StateSpace` system.""" + return self._B + + @B.setter + def B(self, B): + self._B = _atleast_2d_or_none(B) + self.inputs = self.B.shape[-1] + + @property + def C(self): + """Output matrix of the `StateSpace` system.""" + return self._C + + @C.setter + def C(self, C): + self._C = _atleast_2d_or_none(C) + self.outputs = self.C.shape[0] + + @property + def D(self): + """Feedthrough matrix of the `StateSpace` system.""" + return self._D + + @D.setter + def D(self, D): + self._D = _atleast_2d_or_none(D) + + def _copy(self, system): + """ + Copy the parameters of another `StateSpace` system. + + Parameters + ---------- + system : instance of `StateSpace` + The state-space system that is to be copied + + """ + self.A = system.A + self.B = system.B + self.C = system.C + self.D = system.D + + def to_tf(self, **kwargs): + """ + Convert system representation to `TransferFunction`. + + Parameters + ---------- + kwargs : dict, optional + Additional keywords passed to `ss2zpk` + + Returns + ------- + sys : instance of `TransferFunction` + Transfer function of the current system + + """ + return TransferFunction(*ss2tf(self._A, self._B, self._C, self._D, + **kwargs), **self._dt_dict) + + def to_zpk(self, **kwargs): + """ + Convert system representation to `ZerosPolesGain`. + + Parameters + ---------- + kwargs : dict, optional + Additional keywords passed to `ss2zpk` + + Returns + ------- + sys : instance of `ZerosPolesGain` + Zeros, poles, gain representation of the current system + + """ + return ZerosPolesGain(*ss2zpk(self._A, self._B, self._C, self._D, + **kwargs), **self._dt_dict) + + def to_ss(self): + """ + Return a copy of the current `StateSpace` system. + + Returns + ------- + sys : instance of `StateSpace` + The current system (copy) + + """ + return copy.deepcopy(self) + + +class StateSpaceContinuous(StateSpace, lti): + r""" + Continuous-time Linear Time Invariant system in state-space form. + + Represents the system as the continuous-time, first order differential + equation :math:`\dot{x} = A x + B u`. + Continuous-time `StateSpace` systems inherit additional functionality + from the `lti` class. + + Parameters + ---------- + *system: arguments + The `StateSpace` class can be instantiated with 1 or 3 arguments. + The following gives the number of input arguments and their + interpretation: + + * 1: `lti` system: (`StateSpace`, `TransferFunction` or + `ZerosPolesGain`) + * 4: array_like: (A, B, C, D) + + See Also + -------- + TransferFunction, ZerosPolesGain, lti + ss2zpk, ss2tf, zpk2sos + + Notes + ----- + Changing the value of properties that are not part of the + `StateSpace` system representation (such as `zeros` or `poles`) is very + inefficient and may lead to numerical inaccuracies. It is better to + convert to the specific system representation first. For example, call + ``sys = sys.to_zpk()`` before accessing/changing the zeros, poles or gain. + + Examples + -------- + >>> import numpy as np + >>> from scipy import signal + + >>> a = np.array([[0, 1], [0, 0]]) + >>> b = np.array([[0], [1]]) + >>> c = np.array([[1, 0]]) + >>> d = np.array([[0]]) + + >>> sys = signal.StateSpace(a, b, c, d) + >>> print(sys) + StateSpaceContinuous( + array([[0, 1], + [0, 0]]), + array([[0], + [1]]), + array([[1, 0]]), + array([[0]]), + dt: None + ) + + """ + + def to_discrete(self, dt, method='zoh', alpha=None): + """ + Returns the discretized `StateSpace` system. + + Parameters: See `cont2discrete` for details. + + Returns + ------- + sys: instance of `dlti` and `StateSpace` + """ + return StateSpace(*cont2discrete((self.A, self.B, self.C, self.D), + dt, + method=method, + alpha=alpha)[:-1], + dt=dt) + + +class StateSpaceDiscrete(StateSpace, dlti): + r""" + Discrete-time Linear Time Invariant system in state-space form. + + Represents the system as the discrete-time difference equation + :math:`x[k+1] = A x[k] + B u[k]`. + `StateSpace` systems inherit additional functionality from the `dlti` + class. + + Parameters + ---------- + *system: arguments + The `StateSpace` class can be instantiated with 1 or 3 arguments. + The following gives the number of input arguments and their + interpretation: + + * 1: `dlti` system: (`StateSpace`, `TransferFunction` or + `ZerosPolesGain`) + * 4: array_like: (A, B, C, D) + dt: float, optional + Sampling time [s] of the discrete-time systems. Defaults to `True` + (unspecified sampling time). Must be specified as a keyword argument, + for example, ``dt=0.1``. + + See Also + -------- + TransferFunction, ZerosPolesGain, dlti + ss2zpk, ss2tf, zpk2sos + + Notes + ----- + Changing the value of properties that are not part of the + `StateSpace` system representation (such as `zeros` or `poles`) is very + inefficient and may lead to numerical inaccuracies. It is better to + convert to the specific system representation first. For example, call + ``sys = sys.to_zpk()`` before accessing/changing the zeros, poles or gain. + + Examples + -------- + >>> import numpy as np + >>> from scipy import signal + + >>> a = np.array([[1, 0.1], [0, 1]]) + >>> b = np.array([[0.005], [0.1]]) + >>> c = np.array([[1, 0]]) + >>> d = np.array([[0]]) + + >>> signal.StateSpace(a, b, c, d, dt=0.1) + StateSpaceDiscrete( + array([[ 1. , 0.1], + [ 0. , 1. ]]), + array([[ 0.005], + [ 0.1 ]]), + array([[1, 0]]), + array([[0]]), + dt: 0.1 + ) + + """ + pass + + +def lsim(system, U, T, X0=None, interp=True): + """ + Simulate output of a continuous-time linear system. + + Parameters + ---------- + system : an instance of the LTI class or a tuple describing the system. + The following gives the number of elements in the tuple and + the interpretation: + + * 1: (instance of `lti`) + * 2: (num, den) + * 3: (zeros, poles, gain) + * 4: (A, B, C, D) + + U : array_like + An input array describing the input at each time `T` + (interpolation is assumed between given times). If there are + multiple inputs, then each column of the rank-2 array + represents an input. If U = 0 or None, a zero input is used. + T : array_like + The time steps at which the input is defined and at which the + output is desired. Must be nonnegative, increasing, and equally spaced. + X0 : array_like, optional + The initial conditions on the state vector (zero by default). + interp : bool, optional + Whether to use linear (True, the default) or zero-order-hold (False) + interpolation for the input array. + + Returns + ------- + T : 1D ndarray + Time values for the output. + yout : 1D ndarray + System response. + xout : ndarray + Time evolution of the state vector. + + Notes + ----- + If (num, den) is passed in for ``system``, coefficients for both the + numerator and denominator should be specified in descending exponent + order (e.g. ``s^2 + 3s + 5`` would be represented as ``[1, 3, 5]``). + + Examples + -------- + We'll use `lsim` to simulate an analog Bessel filter applied to + a signal. + + >>> import numpy as np + >>> from scipy.signal import bessel, lsim + >>> import matplotlib.pyplot as plt + + Create a low-pass Bessel filter with a cutoff of 12 Hz. + + >>> b, a = bessel(N=5, Wn=2*np.pi*12, btype='lowpass', analog=True) + + Generate data to which the filter is applied. + + >>> t = np.linspace(0, 1.25, 500, endpoint=False) + + The input signal is the sum of three sinusoidal curves, with + frequencies 4 Hz, 40 Hz, and 80 Hz. The filter should mostly + eliminate the 40 Hz and 80 Hz components, leaving just the 4 Hz signal. + + >>> u = (np.cos(2*np.pi*4*t) + 0.6*np.sin(2*np.pi*40*t) + + ... 0.5*np.cos(2*np.pi*80*t)) + + Simulate the filter with `lsim`. + + >>> tout, yout, xout = lsim((b, a), U=u, T=t) + + Plot the result. + + >>> plt.plot(t, u, 'r', alpha=0.5, linewidth=1, label='input') + >>> plt.plot(tout, yout, 'k', linewidth=1.5, label='output') + >>> plt.legend(loc='best', shadow=True, framealpha=1) + >>> plt.grid(alpha=0.3) + >>> plt.xlabel('t') + >>> plt.show() + + In a second example, we simulate a double integrator ``y'' = u``, with + a constant input ``u = 1``. We'll use the state space representation + of the integrator. + + >>> from scipy.signal import lti + >>> A = np.array([[0.0, 1.0], [0.0, 0.0]]) + >>> B = np.array([[0.0], [1.0]]) + >>> C = np.array([[1.0, 0.0]]) + >>> D = 0.0 + >>> system = lti(A, B, C, D) + + `t` and `u` define the time and input signal for the system to + be simulated. + + >>> t = np.linspace(0, 5, num=50) + >>> u = np.ones_like(t) + + Compute the simulation, and then plot `y`. As expected, the plot shows + the curve ``y = 0.5*t**2``. + + >>> tout, y, x = lsim(system, u, t) + >>> plt.plot(t, y) + >>> plt.grid(alpha=0.3) + >>> plt.xlabel('t') + >>> plt.show() + + """ + if isinstance(system, lti): + sys = system._as_ss() + elif isinstance(system, dlti): + raise AttributeError('lsim can only be used with continuous-time ' + 'systems.') + else: + sys = lti(*system)._as_ss() + T = atleast_1d(T) + if len(T.shape) != 1: + raise ValueError("T must be a rank-1 array.") + + A, B, C, D = map(np.asarray, (sys.A, sys.B, sys.C, sys.D)) + n_states = A.shape[0] + n_inputs = B.shape[1] + + n_steps = T.size + if X0 is None: + X0 = zeros(n_states, sys.A.dtype) + xout = np.empty((n_steps, n_states), sys.A.dtype) + + if T[0] == 0: + xout[0] = X0 + elif T[0] > 0: + # step forward to initial time, with zero input + xout[0] = dot(X0, linalg.expm(transpose(A) * T[0])) + else: + raise ValueError("Initial time must be nonnegative") + + no_input = (U is None or + (isinstance(U, (int, float)) and U == 0.) or + not np.any(U)) + + if n_steps == 1: + yout = squeeze(xout @ C.T) + if not no_input: + yout += squeeze(U @ D.T) + return T, yout, squeeze(xout) + + dt = T[1] - T[0] + if not np.allclose(np.diff(T), dt): + raise ValueError("Time steps are not equally spaced.") + + if no_input: + # Zero input: just use matrix exponential + # take transpose because state is a row vector + expAT_dt = linalg.expm(A.T * dt) + for i in range(1, n_steps): + xout[i] = xout[i-1] @ expAT_dt + yout = squeeze(xout @ C.T) + return T, yout, squeeze(xout) + + # Nonzero input + U = atleast_1d(U) + if U.ndim == 1: + U = U[:, np.newaxis] + + if U.shape[0] != n_steps: + raise ValueError("U must have the same number of rows " + "as elements in T.") + + if U.shape[1] != n_inputs: + raise ValueError("System does not define that many inputs.") + + if not interp: + # Zero-order hold + # Algorithm: to integrate from time 0 to time dt, we solve + # xdot = A x + B u, x(0) = x0 + # udot = 0, u(0) = u0. + # + # Solution is + # [ x(dt) ] [ A*dt B*dt ] [ x0 ] + # [ u(dt) ] = exp [ 0 0 ] [ u0 ] + M = np.vstack([np.hstack([A * dt, B * dt]), + np.zeros((n_inputs, n_states + n_inputs))]) + # transpose everything because the state and input are row vectors + expMT = linalg.expm(M.T) + Ad = expMT[:n_states, :n_states] + Bd = expMT[n_states:, :n_states] + for i in range(1, n_steps): + xout[i] = xout[i-1] @ Ad + U[i-1] @ Bd + else: + # Linear interpolation between steps + # Algorithm: to integrate from time 0 to time dt, with linear + # interpolation between inputs u(0) = u0 and u(dt) = u1, we solve + # xdot = A x + B u, x(0) = x0 + # udot = (u1 - u0) / dt, u(0) = u0. + # + # Solution is + # [ x(dt) ] [ A*dt B*dt 0 ] [ x0 ] + # [ u(dt) ] = exp [ 0 0 I ] [ u0 ] + # [u1 - u0] [ 0 0 0 ] [u1 - u0] + M = np.vstack([np.hstack([A * dt, B * dt, + np.zeros((n_states, n_inputs))]), + np.hstack([np.zeros((n_inputs, n_states + n_inputs)), + np.identity(n_inputs)]), + np.zeros((n_inputs, n_states + 2 * n_inputs))]) + expMT = linalg.expm(M.T) + Ad = expMT[:n_states, :n_states] + Bd1 = expMT[n_states+n_inputs:, :n_states] + Bd0 = expMT[n_states:n_states + n_inputs, :n_states] - Bd1 + for i in range(1, n_steps): + xout[i] = xout[i-1] @ Ad + U[i-1] @ Bd0 + U[i] @ Bd1 + + yout = squeeze(xout @ C.T) + squeeze(U @ D.T) + return T, yout, squeeze(xout) + + +def _default_response_times(A, n): + """Compute a reasonable set of time samples for the response time. + + This function is used by `impulse` and `step` to compute the response time + when the `T` argument to the function is None. + + Parameters + ---------- + A : array_like + The system matrix, which is square. + n : int + The number of time samples to generate. + + Returns + ------- + t : ndarray + The 1-D array of length `n` of time samples at which the response + is to be computed. + """ + # Create a reasonable time interval. + # TODO: This could use some more work. + # For example, what is expected when the system is unstable? + vals = linalg.eigvals(A) + r = min(abs(real(vals))) + if r == 0.0: + r = 1.0 + tc = 1.0 / r + t = linspace(0.0, 7 * tc, n) + return t + + +def impulse(system, X0=None, T=None, N=None): + """Impulse response of continuous-time system. + + Parameters + ---------- + system : an instance of the LTI class or a tuple of array_like + describing the system. + The following gives the number of elements in the tuple and + the interpretation: + + * 1 (instance of `lti`) + * 2 (num, den) + * 3 (zeros, poles, gain) + * 4 (A, B, C, D) + + X0 : array_like, optional + Initial state-vector. Defaults to zero. + T : array_like, optional + Time points. Computed if not given. + N : int, optional + The number of time points to compute (if `T` is not given). + + Returns + ------- + T : ndarray + A 1-D array of time points. + yout : ndarray + A 1-D array containing the impulse response of the system (except for + singularities at zero). + + Notes + ----- + If (num, den) is passed in for ``system``, coefficients for both the + numerator and denominator should be specified in descending exponent + order (e.g. ``s^2 + 3s + 5`` would be represented as ``[1, 3, 5]``). + + Examples + -------- + Compute the impulse response of a second order system with a repeated + root: ``x''(t) + 2*x'(t) + x(t) = u(t)`` + + >>> from scipy import signal + >>> system = ([1.0], [1.0, 2.0, 1.0]) + >>> t, y = signal.impulse(system) + >>> import matplotlib.pyplot as plt + >>> plt.plot(t, y) + + """ + if isinstance(system, lti): + sys = system._as_ss() + elif isinstance(system, dlti): + raise AttributeError('impulse can only be used with continuous-time ' + 'systems.') + else: + sys = lti(*system)._as_ss() + if X0 is None: + X = squeeze(sys.B) + else: + X = squeeze(sys.B + X0) + if N is None: + N = 100 + if T is None: + T = _default_response_times(sys.A, N) + else: + T = asarray(T) + + _, h, _ = lsim(sys, 0., T, X, interp=False) + return T, h + + +def step(system, X0=None, T=None, N=None): + """Step response of continuous-time system. + + Parameters + ---------- + system : an instance of the LTI class or a tuple of array_like + describing the system. + The following gives the number of elements in the tuple and + the interpretation: + + * 1 (instance of `lti`) + * 2 (num, den) + * 3 (zeros, poles, gain) + * 4 (A, B, C, D) + + X0 : array_like, optional + Initial state-vector (default is zero). + T : array_like, optional + Time points (computed if not given). + N : int, optional + Number of time points to compute if `T` is not given. + + Returns + ------- + T : 1D ndarray + Output time points. + yout : 1D ndarray + Step response of system. + + + Notes + ----- + If (num, den) is passed in for ``system``, coefficients for both the + numerator and denominator should be specified in descending exponent + order (e.g. ``s^2 + 3s + 5`` would be represented as ``[1, 3, 5]``). + + Examples + -------- + >>> from scipy import signal + >>> import matplotlib.pyplot as plt + >>> lti = signal.lti([1.0], [1.0, 1.0]) + >>> t, y = signal.step(lti) + >>> plt.plot(t, y) + >>> plt.xlabel('Time [s]') + >>> plt.ylabel('Amplitude') + >>> plt.title('Step response for 1. Order Lowpass') + >>> plt.grid() + + """ + if isinstance(system, lti): + sys = system._as_ss() + elif isinstance(system, dlti): + raise AttributeError('step can only be used with continuous-time ' + 'systems.') + else: + sys = lti(*system)._as_ss() + if N is None: + N = 100 + if T is None: + T = _default_response_times(sys.A, N) + else: + T = asarray(T) + U = ones(T.shape, sys.A.dtype) + vals = lsim(sys, U, T, X0=X0, interp=False) + return vals[0], vals[1] + + +def bode(system, w=None, n=100): + """ + Calculate Bode magnitude and phase data of a continuous-time system. + + Parameters + ---------- + system : an instance of the LTI class or a tuple describing the system. + The following gives the number of elements in the tuple and + the interpretation: + + * 1 (instance of `lti`) + * 2 (num, den) + * 3 (zeros, poles, gain) + * 4 (A, B, C, D) + + w : array_like, optional + Array of frequencies (in rad/s). Magnitude and phase data is calculated + for every value in this array. If not given a reasonable set will be + calculated. + n : int, optional + Number of frequency points to compute if `w` is not given. The `n` + frequencies are logarithmically spaced in an interval chosen to + include the influence of the poles and zeros of the system. + + Returns + ------- + w : 1D ndarray + Frequency array [rad/s] + mag : 1D ndarray + Magnitude array [dB] + phase : 1D ndarray + Phase array [deg] + + Notes + ----- + If (num, den) is passed in for ``system``, coefficients for both the + numerator and denominator should be specified in descending exponent + order (e.g. ``s^2 + 3s + 5`` would be represented as ``[1, 3, 5]``). + + .. versionadded:: 0.11.0 + + Examples + -------- + >>> from scipy import signal + >>> import matplotlib.pyplot as plt + + >>> sys = signal.TransferFunction([1], [1, 1]) + >>> w, mag, phase = signal.bode(sys) + + >>> plt.figure() + >>> plt.semilogx(w, mag) # Bode magnitude plot + >>> plt.figure() + >>> plt.semilogx(w, phase) # Bode phase plot + >>> plt.show() + + """ + w, y = freqresp(system, w=w, n=n) + + mag = 20.0 * numpy.log10(abs(y)) + phase = numpy.unwrap(numpy.arctan2(y.imag, y.real)) * 180.0 / numpy.pi + + return w, mag, phase + + +def freqresp(system, w=None, n=10000): + r"""Calculate the frequency response of a continuous-time system. + + Parameters + ---------- + system : an instance of the `lti` class or a tuple describing the system. + The following gives the number of elements in the tuple and + the interpretation: + + * 1 (instance of `lti`) + * 2 (num, den) + * 3 (zeros, poles, gain) + * 4 (A, B, C, D) + + w : array_like, optional + Array of frequencies (in rad/s). Magnitude and phase data is + calculated for every value in this array. If not given, a reasonable + set will be calculated. + n : int, optional + Number of frequency points to compute if `w` is not given. The `n` + frequencies are logarithmically spaced in an interval chosen to + include the influence of the poles and zeros of the system. + + Returns + ------- + w : 1D ndarray + Frequency array [rad/s] + H : 1D ndarray + Array of complex magnitude values + + Notes + ----- + If (num, den) is passed in for ``system``, coefficients for both the + numerator and denominator should be specified in descending exponent + order (e.g. ``s^2 + 3s + 5`` would be represented as ``[1, 3, 5]``). + + Examples + -------- + Generating the Nyquist plot of a transfer function + + >>> from scipy import signal + >>> import matplotlib.pyplot as plt + + Construct the transfer function :math:`H(s) = \frac{5}{(s-1)^3}`: + + >>> s1 = signal.ZerosPolesGain([], [1, 1, 1], [5]) + + >>> w, H = signal.freqresp(s1) + + >>> plt.figure() + >>> plt.plot(H.real, H.imag, "b") + >>> plt.plot(H.real, -H.imag, "r") + >>> plt.show() + """ + if isinstance(system, lti): + if isinstance(system, (TransferFunction, ZerosPolesGain)): + sys = system + else: + sys = system._as_zpk() + elif isinstance(system, dlti): + raise AttributeError('freqresp can only be used with continuous-time ' + 'systems.') + else: + sys = lti(*system)._as_zpk() + + if sys.inputs != 1 or sys.outputs != 1: + raise ValueError("freqresp() requires a SISO (single input, single " + "output) system.") + + if w is not None: + worN = w + else: + worN = n + + if isinstance(sys, TransferFunction): + # In the call to freqs(), sys.num.ravel() is used because there are + # cases where sys.num is a 2-D array with a single row. + w, h = freqs(sys.num.ravel(), sys.den, worN=worN) + + elif isinstance(sys, ZerosPolesGain): + w, h = freqs_zpk(sys.zeros, sys.poles, sys.gain, worN=worN) + + return w, h + + +# This class will be used by place_poles to return its results +# see https://code.activestate.com/recipes/52308/ +class Bunch: + def __init__(self, **kwds): + self.__dict__.update(kwds) + + +def _valid_inputs(A, B, poles, method, rtol, maxiter): + """ + Check the poles come in complex conjugage pairs + Check shapes of A, B and poles are compatible. + Check the method chosen is compatible with provided poles + Return update method to use and ordered poles + + """ + poles = np.asarray(poles) + if poles.ndim > 1: + raise ValueError("Poles must be a 1D array like.") + # Will raise ValueError if poles do not come in complex conjugates pairs + poles = _order_complex_poles(poles) + if A.ndim > 2: + raise ValueError("A must be a 2D array/matrix.") + if B.ndim > 2: + raise ValueError("B must be a 2D array/matrix") + if A.shape[0] != A.shape[1]: + raise ValueError("A must be square") + if len(poles) > A.shape[0]: + raise ValueError("maximum number of poles is %d but you asked for %d" % + (A.shape[0], len(poles))) + if len(poles) < A.shape[0]: + raise ValueError("number of poles is %d but you should provide %d" % + (len(poles), A.shape[0])) + r = np.linalg.matrix_rank(B) + for p in poles: + if sum(p == poles) > r: + raise ValueError("at least one of the requested pole is repeated " + "more than rank(B) times") + # Choose update method + update_loop = _YT_loop + if method not in ('KNV0','YT'): + raise ValueError("The method keyword must be one of 'YT' or 'KNV0'") + + if method == "KNV0": + update_loop = _KNV0_loop + if not all(np.isreal(poles)): + raise ValueError("Complex poles are not supported by KNV0") + + if maxiter < 1: + raise ValueError("maxiter must be at least equal to 1") + + # We do not check rtol <= 0 as the user can use a negative rtol to + # force maxiter iterations + if rtol > 1: + raise ValueError("rtol can not be greater than 1") + + return update_loop, poles + + +def _order_complex_poles(poles): + """ + Check we have complex conjugates pairs and reorder P according to YT, ie + real_poles, complex_i, conjugate complex_i, .... + The lexicographic sort on the complex poles is added to help the user to + compare sets of poles. + """ + ordered_poles = np.sort(poles[np.isreal(poles)]) + im_poles = [] + for p in np.sort(poles[np.imag(poles) < 0]): + if np.conj(p) in poles: + im_poles.extend((p, np.conj(p))) + + ordered_poles = np.hstack((ordered_poles, im_poles)) + + if poles.shape[0] != len(ordered_poles): + raise ValueError("Complex poles must come with their conjugates") + return ordered_poles + + +def _KNV0(B, ker_pole, transfer_matrix, j, poles): + """ + Algorithm "KNV0" Kautsky et Al. Robust pole + assignment in linear state feedback, Int journal of Control + 1985, vol 41 p 1129->1155 + https://la.epfl.ch/files/content/sites/la/files/ + users/105941/public/KautskyNicholsDooren + + """ + # Remove xj form the base + transfer_matrix_not_j = np.delete(transfer_matrix, j, axis=1) + # If we QR this matrix in full mode Q=Q0|Q1 + # then Q1 will be a single column orthogonnal to + # Q0, that's what we are looking for ! + + # After merge of gh-4249 great speed improvements could be achieved + # using QR updates instead of full QR in the line below + + # To debug with numpy qr uncomment the line below + # Q, R = np.linalg.qr(transfer_matrix_not_j, mode="complete") + Q, R = s_qr(transfer_matrix_not_j, mode="full") + + mat_ker_pj = np.dot(ker_pole[j], ker_pole[j].T) + yj = np.dot(mat_ker_pj, Q[:, -1]) + + # If Q[:, -1] is "almost" orthogonal to ker_pole[j] its + # projection into ker_pole[j] will yield a vector + # close to 0. As we are looking for a vector in ker_pole[j] + # simply stick with transfer_matrix[:, j] (unless someone provides me with + # a better choice ?) + + if not np.allclose(yj, 0): + xj = yj/np.linalg.norm(yj) + transfer_matrix[:, j] = xj + + # KNV does not support complex poles, using YT technique the two lines + # below seem to work 9 out of 10 times but it is not reliable enough: + # transfer_matrix[:, j]=real(xj) + # transfer_matrix[:, j+1]=imag(xj) + + # Add this at the beginning of this function if you wish to test + # complex support: + # if ~np.isreal(P[j]) and (j>=B.shape[0]-1 or P[j]!=np.conj(P[j+1])): + # return + # Problems arise when imag(xj)=>0 I have no idea on how to fix this + + +def _YT_real(ker_pole, Q, transfer_matrix, i, j): + """ + Applies algorithm from YT section 6.1 page 19 related to real pairs + """ + # step 1 page 19 + u = Q[:, -2, np.newaxis] + v = Q[:, -1, np.newaxis] + + # step 2 page 19 + m = np.dot(np.dot(ker_pole[i].T, np.dot(u, v.T) - + np.dot(v, u.T)), ker_pole[j]) + + # step 3 page 19 + um, sm, vm = np.linalg.svd(m) + # mu1, mu2 two first columns of U => 2 first lines of U.T + mu1, mu2 = um.T[:2, :, np.newaxis] + # VM is V.T with numpy we want the first two lines of V.T + nu1, nu2 = vm[:2, :, np.newaxis] + + # what follows is a rough python translation of the formulas + # in section 6.2 page 20 (step 4) + transfer_matrix_j_mo_transfer_matrix_j = np.vstack(( + transfer_matrix[:, i, np.newaxis], + transfer_matrix[:, j, np.newaxis])) + + if not np.allclose(sm[0], sm[1]): + ker_pole_imo_mu1 = np.dot(ker_pole[i], mu1) + ker_pole_i_nu1 = np.dot(ker_pole[j], nu1) + ker_pole_mu_nu = np.vstack((ker_pole_imo_mu1, ker_pole_i_nu1)) + else: + ker_pole_ij = np.vstack(( + np.hstack((ker_pole[i], + np.zeros(ker_pole[i].shape))), + np.hstack((np.zeros(ker_pole[j].shape), + ker_pole[j])) + )) + mu_nu_matrix = np.vstack( + (np.hstack((mu1, mu2)), np.hstack((nu1, nu2))) + ) + ker_pole_mu_nu = np.dot(ker_pole_ij, mu_nu_matrix) + transfer_matrix_ij = np.dot(np.dot(ker_pole_mu_nu, ker_pole_mu_nu.T), + transfer_matrix_j_mo_transfer_matrix_j) + if not np.allclose(transfer_matrix_ij, 0): + transfer_matrix_ij = (np.sqrt(2)*transfer_matrix_ij / + np.linalg.norm(transfer_matrix_ij)) + transfer_matrix[:, i] = transfer_matrix_ij[ + :transfer_matrix[:, i].shape[0], 0 + ] + transfer_matrix[:, j] = transfer_matrix_ij[ + transfer_matrix[:, i].shape[0]:, 0 + ] + else: + # As in knv0 if transfer_matrix_j_mo_transfer_matrix_j is orthogonal to + # Vect{ker_pole_mu_nu} assign transfer_matrixi/transfer_matrix_j to + # ker_pole_mu_nu and iterate. As we are looking for a vector in + # Vect{Matker_pole_MU_NU} (see section 6.1 page 19) this might help + # (that's a guess, not a claim !) + transfer_matrix[:, i] = ker_pole_mu_nu[ + :transfer_matrix[:, i].shape[0], 0 + ] + transfer_matrix[:, j] = ker_pole_mu_nu[ + transfer_matrix[:, i].shape[0]:, 0 + ] + + +def _YT_complex(ker_pole, Q, transfer_matrix, i, j): + """ + Applies algorithm from YT section 6.2 page 20 related to complex pairs + """ + # step 1 page 20 + ur = np.sqrt(2)*Q[:, -2, np.newaxis] + ui = np.sqrt(2)*Q[:, -1, np.newaxis] + u = ur + 1j*ui + + # step 2 page 20 + ker_pole_ij = ker_pole[i] + m = np.dot(np.dot(np.conj(ker_pole_ij.T), np.dot(u, np.conj(u).T) - + np.dot(np.conj(u), u.T)), ker_pole_ij) + + # step 3 page 20 + e_val, e_vec = np.linalg.eig(m) + # sort eigenvalues according to their module + e_val_idx = np.argsort(np.abs(e_val)) + mu1 = e_vec[:, e_val_idx[-1], np.newaxis] + mu2 = e_vec[:, e_val_idx[-2], np.newaxis] + + # what follows is a rough python translation of the formulas + # in section 6.2 page 20 (step 4) + + # remember transfer_matrix_i has been split as + # transfer_matrix[i]=real(transfer_matrix_i) and + # transfer_matrix[j]=imag(transfer_matrix_i) + transfer_matrix_j_mo_transfer_matrix_j = ( + transfer_matrix[:, i, np.newaxis] + + 1j*transfer_matrix[:, j, np.newaxis] + ) + if not np.allclose(np.abs(e_val[e_val_idx[-1]]), + np.abs(e_val[e_val_idx[-2]])): + ker_pole_mu = np.dot(ker_pole_ij, mu1) + else: + mu1_mu2_matrix = np.hstack((mu1, mu2)) + ker_pole_mu = np.dot(ker_pole_ij, mu1_mu2_matrix) + transfer_matrix_i_j = np.dot(np.dot(ker_pole_mu, np.conj(ker_pole_mu.T)), + transfer_matrix_j_mo_transfer_matrix_j) + + if not np.allclose(transfer_matrix_i_j, 0): + transfer_matrix_i_j = (transfer_matrix_i_j / + np.linalg.norm(transfer_matrix_i_j)) + transfer_matrix[:, i] = np.real(transfer_matrix_i_j[:, 0]) + transfer_matrix[:, j] = np.imag(transfer_matrix_i_j[:, 0]) + else: + # same idea as in YT_real + transfer_matrix[:, i] = np.real(ker_pole_mu[:, 0]) + transfer_matrix[:, j] = np.imag(ker_pole_mu[:, 0]) + + +def _YT_loop(ker_pole, transfer_matrix, poles, B, maxiter, rtol): + """ + Algorithm "YT" Tits, Yang. Globally Convergent + Algorithms for Robust Pole Assignment by State Feedback + https://hdl.handle.net/1903/5598 + The poles P have to be sorted accordingly to section 6.2 page 20 + + """ + # The IEEE edition of the YT paper gives useful information on the + # optimal update order for the real poles in order to minimize the number + # of times we have to loop over all poles, see page 1442 + nb_real = poles[np.isreal(poles)].shape[0] + # hnb => Half Nb Real + hnb = nb_real // 2 + + # Stick to the indices in the paper and then remove one to get numpy array + # index it is a bit easier to link the code to the paper this way even if it + # is not very clean. The paper is unclear about what should be done when + # there is only one real pole => use KNV0 on this real pole seem to work + if nb_real > 0: + #update the biggest real pole with the smallest one + update_order = [[nb_real], [1]] + else: + update_order = [[],[]] + + r_comp = np.arange(nb_real+1, len(poles)+1, 2) + # step 1.a + r_p = np.arange(1, hnb+nb_real % 2) + update_order[0].extend(2*r_p) + update_order[1].extend(2*r_p+1) + # step 1.b + update_order[0].extend(r_comp) + update_order[1].extend(r_comp+1) + # step 1.c + r_p = np.arange(1, hnb+1) + update_order[0].extend(2*r_p-1) + update_order[1].extend(2*r_p) + # step 1.d + if hnb == 0 and np.isreal(poles[0]): + update_order[0].append(1) + update_order[1].append(1) + update_order[0].extend(r_comp) + update_order[1].extend(r_comp+1) + # step 2.a + r_j = np.arange(2, hnb+nb_real % 2) + for j in r_j: + for i in range(1, hnb+1): + update_order[0].append(i) + update_order[1].append(i+j) + # step 2.b + if hnb == 0 and np.isreal(poles[0]): + update_order[0].append(1) + update_order[1].append(1) + update_order[0].extend(r_comp) + update_order[1].extend(r_comp+1) + # step 2.c + r_j = np.arange(2, hnb+nb_real % 2) + for j in r_j: + for i in range(hnb+1, nb_real+1): + idx_1 = i+j + if idx_1 > nb_real: + idx_1 = i+j-nb_real + update_order[0].append(i) + update_order[1].append(idx_1) + # step 2.d + if hnb == 0 and np.isreal(poles[0]): + update_order[0].append(1) + update_order[1].append(1) + update_order[0].extend(r_comp) + update_order[1].extend(r_comp+1) + # step 3.a + for i in range(1, hnb+1): + update_order[0].append(i) + update_order[1].append(i+hnb) + # step 3.b + if hnb == 0 and np.isreal(poles[0]): + update_order[0].append(1) + update_order[1].append(1) + update_order[0].extend(r_comp) + update_order[1].extend(r_comp+1) + + update_order = np.array(update_order).T-1 + stop = False + nb_try = 0 + while nb_try < maxiter and not stop: + det_transfer_matrixb = np.abs(np.linalg.det(transfer_matrix)) + for i, j in update_order: + if i == j: + assert i == 0, "i!=0 for KNV call in YT" + assert np.isreal(poles[i]), "calling KNV on a complex pole" + _KNV0(B, ker_pole, transfer_matrix, i, poles) + else: + transfer_matrix_not_i_j = np.delete(transfer_matrix, (i, j), + axis=1) + # after merge of gh-4249 great speed improvements could be + # achieved using QR updates instead of full QR in the line below + + #to debug with numpy qr uncomment the line below + #Q, _ = np.linalg.qr(transfer_matrix_not_i_j, mode="complete") + Q, _ = s_qr(transfer_matrix_not_i_j, mode="full") + + if np.isreal(poles[i]): + assert np.isreal(poles[j]), "mixing real and complex " + \ + "in YT_real" + str(poles) + _YT_real(ker_pole, Q, transfer_matrix, i, j) + else: + assert ~np.isreal(poles[i]), "mixing real and complex " + \ + "in YT_real" + str(poles) + _YT_complex(ker_pole, Q, transfer_matrix, i, j) + + det_transfer_matrix = np.max((np.sqrt(np.spacing(1)), + np.abs(np.linalg.det(transfer_matrix)))) + cur_rtol = np.abs( + (det_transfer_matrix - + det_transfer_matrixb) / + det_transfer_matrix) + if cur_rtol < rtol and det_transfer_matrix > np.sqrt(np.spacing(1)): + # Convergence test from YT page 21 + stop = True + nb_try += 1 + return stop, cur_rtol, nb_try + + +def _KNV0_loop(ker_pole, transfer_matrix, poles, B, maxiter, rtol): + """ + Loop over all poles one by one and apply KNV method 0 algorithm + """ + # This method is useful only because we need to be able to call + # _KNV0 from YT without looping over all poles, otherwise it would + # have been fine to mix _KNV0_loop and _KNV0 in a single function + stop = False + nb_try = 0 + while nb_try < maxiter and not stop: + det_transfer_matrixb = np.abs(np.linalg.det(transfer_matrix)) + for j in range(B.shape[0]): + _KNV0(B, ker_pole, transfer_matrix, j, poles) + + det_transfer_matrix = np.max((np.sqrt(np.spacing(1)), + np.abs(np.linalg.det(transfer_matrix)))) + cur_rtol = np.abs((det_transfer_matrix - det_transfer_matrixb) / + det_transfer_matrix) + if cur_rtol < rtol and det_transfer_matrix > np.sqrt(np.spacing(1)): + # Convergence test from YT page 21 + stop = True + + nb_try += 1 + return stop, cur_rtol, nb_try + + +def place_poles(A, B, poles, method="YT", rtol=1e-3, maxiter=30): + """ + Compute K such that eigenvalues (A - dot(B, K))=poles. + + K is the gain matrix such as the plant described by the linear system + ``AX+BU`` will have its closed-loop poles, i.e the eigenvalues ``A - B*K``, + as close as possible to those asked for in poles. + + SISO, MISO and MIMO systems are supported. + + Parameters + ---------- + A, B : ndarray + State-space representation of linear system ``AX + BU``. + poles : array_like + Desired real poles and/or complex conjugates poles. + Complex poles are only supported with ``method="YT"`` (default). + method: {'YT', 'KNV0'}, optional + Which method to choose to find the gain matrix K. One of: + + - 'YT': Yang Tits + - 'KNV0': Kautsky, Nichols, Van Dooren update method 0 + + See References and Notes for details on the algorithms. + rtol: float, optional + After each iteration the determinant of the eigenvectors of + ``A - B*K`` is compared to its previous value, when the relative + error between these two values becomes lower than `rtol` the algorithm + stops. Default is 1e-3. + maxiter: int, optional + Maximum number of iterations to compute the gain matrix. + Default is 30. + + Returns + ------- + full_state_feedback : Bunch object + full_state_feedback is composed of: + gain_matrix : 1-D ndarray + The closed loop matrix K such as the eigenvalues of ``A-BK`` + are as close as possible to the requested poles. + computed_poles : 1-D ndarray + The poles corresponding to ``A-BK`` sorted as first the real + poles in increasing order, then the complex congugates in + lexicographic order. + requested_poles : 1-D ndarray + The poles the algorithm was asked to place sorted as above, + they may differ from what was achieved. + X : 2-D ndarray + The transfer matrix such as ``X * diag(poles) = (A - B*K)*X`` + (see Notes) + rtol : float + The relative tolerance achieved on ``det(X)`` (see Notes). + `rtol` will be NaN if it is possible to solve the system + ``diag(poles) = (A - B*K)``, or 0 when the optimization + algorithms can't do anything i.e when ``B.shape[1] == 1``. + nb_iter : int + The number of iterations performed before converging. + `nb_iter` will be NaN if it is possible to solve the system + ``diag(poles) = (A - B*K)``, or 0 when the optimization + algorithms can't do anything i.e when ``B.shape[1] == 1``. + + Notes + ----- + The Tits and Yang (YT), [2]_ paper is an update of the original Kautsky et + al. (KNV) paper [1]_. KNV relies on rank-1 updates to find the transfer + matrix X such that ``X * diag(poles) = (A - B*K)*X``, whereas YT uses + rank-2 updates. This yields on average more robust solutions (see [2]_ + pp 21-22), furthermore the YT algorithm supports complex poles whereas KNV + does not in its original version. Only update method 0 proposed by KNV has + been implemented here, hence the name ``'KNV0'``. + + KNV extended to complex poles is used in Matlab's ``place`` function, YT is + distributed under a non-free licence by Slicot under the name ``robpole``. + It is unclear and undocumented how KNV0 has been extended to complex poles + (Tits and Yang claim on page 14 of their paper that their method can not be + used to extend KNV to complex poles), therefore only YT supports them in + this implementation. + + As the solution to the problem of pole placement is not unique for MIMO + systems, both methods start with a tentative transfer matrix which is + altered in various way to increase its determinant. Both methods have been + proven to converge to a stable solution, however depending on the way the + initial transfer matrix is chosen they will converge to different + solutions and therefore there is absolutely no guarantee that using + ``'KNV0'`` will yield results similar to Matlab's or any other + implementation of these algorithms. + + Using the default method ``'YT'`` should be fine in most cases; ``'KNV0'`` + is only provided because it is needed by ``'YT'`` in some specific cases. + Furthermore ``'YT'`` gives on average more robust results than ``'KNV0'`` + when ``abs(det(X))`` is used as a robustness indicator. + + [2]_ is available as a technical report on the following URL: + https://hdl.handle.net/1903/5598 + + References + ---------- + .. [1] J. Kautsky, N.K. Nichols and P. van Dooren, "Robust pole assignment + in linear state feedback", International Journal of Control, Vol. 41 + pp. 1129-1155, 1985. + .. [2] A.L. Tits and Y. Yang, "Globally convergent algorithms for robust + pole assignment by state feedback", IEEE Transactions on Automatic + Control, Vol. 41, pp. 1432-1452, 1996. + + Examples + -------- + A simple example demonstrating real pole placement using both KNV and YT + algorithms. This is example number 1 from section 4 of the reference KNV + publication ([1]_): + + >>> import numpy as np + >>> from scipy import signal + >>> import matplotlib.pyplot as plt + + >>> A = np.array([[ 1.380, -0.2077, 6.715, -5.676 ], + ... [-0.5814, -4.290, 0, 0.6750 ], + ... [ 1.067, 4.273, -6.654, 5.893 ], + ... [ 0.0480, 4.273, 1.343, -2.104 ]]) + >>> B = np.array([[ 0, 5.679 ], + ... [ 1.136, 1.136 ], + ... [ 0, 0, ], + ... [-3.146, 0 ]]) + >>> P = np.array([-0.2, -0.5, -5.0566, -8.6659]) + + Now compute K with KNV method 0, with the default YT method and with the YT + method while forcing 100 iterations of the algorithm and print some results + after each call. + + >>> fsf1 = signal.place_poles(A, B, P, method='KNV0') + >>> fsf1.gain_matrix + array([[ 0.20071427, -0.96665799, 0.24066128, -0.10279785], + [ 0.50587268, 0.57779091, 0.51795763, -0.41991442]]) + + >>> fsf2 = signal.place_poles(A, B, P) # uses YT method + >>> fsf2.computed_poles + array([-8.6659, -5.0566, -0.5 , -0.2 ]) + + >>> fsf3 = signal.place_poles(A, B, P, rtol=-1, maxiter=100) + >>> fsf3.X + array([[ 0.52072442+0.j, -0.08409372+0.j, -0.56847937+0.j, 0.74823657+0.j], + [-0.04977751+0.j, -0.80872954+0.j, 0.13566234+0.j, -0.29322906+0.j], + [-0.82266932+0.j, -0.19168026+0.j, -0.56348322+0.j, -0.43815060+0.j], + [ 0.22267347+0.j, 0.54967577+0.j, -0.58387806+0.j, -0.40271926+0.j]]) + + The absolute value of the determinant of X is a good indicator to check the + robustness of the results, both ``'KNV0'`` and ``'YT'`` aim at maximizing + it. Below a comparison of the robustness of the results above: + + >>> abs(np.linalg.det(fsf1.X)) < abs(np.linalg.det(fsf2.X)) + True + >>> abs(np.linalg.det(fsf2.X)) < abs(np.linalg.det(fsf3.X)) + True + + Now a simple example for complex poles: + + >>> A = np.array([[ 0, 7/3., 0, 0 ], + ... [ 0, 0, 0, 7/9. ], + ... [ 0, 0, 0, 0 ], + ... [ 0, 0, 0, 0 ]]) + >>> B = np.array([[ 0, 0 ], + ... [ 0, 0 ], + ... [ 1, 0 ], + ... [ 0, 1 ]]) + >>> P = np.array([-3, -1, -2-1j, -2+1j]) / 3. + >>> fsf = signal.place_poles(A, B, P, method='YT') + + We can plot the desired and computed poles in the complex plane: + + >>> t = np.linspace(0, 2*np.pi, 401) + >>> plt.plot(np.cos(t), np.sin(t), 'k--') # unit circle + >>> plt.plot(fsf.requested_poles.real, fsf.requested_poles.imag, + ... 'wo', label='Desired') + >>> plt.plot(fsf.computed_poles.real, fsf.computed_poles.imag, 'bx', + ... label='Placed') + >>> plt.grid() + >>> plt.axis('image') + >>> plt.axis([-1.1, 1.1, -1.1, 1.1]) + >>> plt.legend(bbox_to_anchor=(1.05, 1), loc=2, numpoints=1) + + """ + # Move away all the inputs checking, it only adds noise to the code + update_loop, poles = _valid_inputs(A, B, poles, method, rtol, maxiter) + + # The current value of the relative tolerance we achieved + cur_rtol = 0 + # The number of iterations needed before converging + nb_iter = 0 + + # Step A: QR decomposition of B page 1132 KN + # to debug with numpy qr uncomment the line below + # u, z = np.linalg.qr(B, mode="complete") + u, z = s_qr(B, mode="full") + rankB = np.linalg.matrix_rank(B) + u0 = u[:, :rankB] + u1 = u[:, rankB:] + z = z[:rankB, :] + + # If we can use the identity matrix as X the solution is obvious + if B.shape[0] == rankB: + # if B is square and full rank there is only one solution + # such as (A+BK)=inv(X)*diag(P)*X with X=eye(A.shape[0]) + # i.e K=inv(B)*(diag(P)-A) + # if B has as many lines as its rank (but not square) there are many + # solutions and we can choose one using least squares + # => use lstsq in both cases. + # In both cases the transfer matrix X will be eye(A.shape[0]) and I + # can hardly think of a better one so there is nothing to optimize + # + # for complex poles we use the following trick + # + # |a -b| has for eigenvalues a+b and a-b + # |b a| + # + # |a+bi 0| has the obvious eigenvalues a+bi and a-bi + # |0 a-bi| + # + # e.g solving the first one in R gives the solution + # for the second one in C + diag_poles = np.zeros(A.shape) + idx = 0 + while idx < poles.shape[0]: + p = poles[idx] + diag_poles[idx, idx] = np.real(p) + if ~np.isreal(p): + diag_poles[idx, idx+1] = -np.imag(p) + diag_poles[idx+1, idx+1] = np.real(p) + diag_poles[idx+1, idx] = np.imag(p) + idx += 1 # skip next one + idx += 1 + gain_matrix = np.linalg.lstsq(B, diag_poles-A, rcond=-1)[0] + transfer_matrix = np.eye(A.shape[0]) + cur_rtol = np.nan + nb_iter = np.nan + else: + # step A (p1144 KNV) and beginning of step F: decompose + # dot(U1.T, A-P[i]*I).T and build our set of transfer_matrix vectors + # in the same loop + ker_pole = [] + + # flag to skip the conjugate of a complex pole + skip_conjugate = False + # select orthonormal base ker_pole for each Pole and vectors for + # transfer_matrix + for j in range(B.shape[0]): + if skip_conjugate: + skip_conjugate = False + continue + pole_space_j = np.dot(u1.T, A-poles[j]*np.eye(B.shape[0])).T + + # after QR Q=Q0|Q1 + # only Q0 is used to reconstruct the qr'ed (dot Q, R) matrix. + # Q1 is orthogonnal to Q0 and will be multiplied by the zeros in + # R when using mode "complete". In default mode Q1 and the zeros + # in R are not computed + + # To debug with numpy qr uncomment the line below + # Q, _ = np.linalg.qr(pole_space_j, mode="complete") + Q, _ = s_qr(pole_space_j, mode="full") + + ker_pole_j = Q[:, pole_space_j.shape[1]:] + + # We want to select one vector in ker_pole_j to build the transfer + # matrix, however qr returns sometimes vectors with zeros on the + # same line for each pole and this yields very long convergence + # times. + # Or some other times a set of vectors, one with zero imaginary + # part and one (or several) with imaginary parts. After trying + # many ways to select the best possible one (eg ditch vectors + # with zero imaginary part for complex poles) I ended up summing + # all vectors in ker_pole_j, this solves 100% of the problems and + # is a valid choice for transfer_matrix. + # This way for complex poles we are sure to have a non zero + # imaginary part that way, and the problem of lines full of zeros + # in transfer_matrix is solved too as when a vector from + # ker_pole_j has a zero the other one(s) when + # ker_pole_j.shape[1]>1) for sure won't have a zero there. + + transfer_matrix_j = np.sum(ker_pole_j, axis=1)[:, np.newaxis] + transfer_matrix_j = (transfer_matrix_j / + np.linalg.norm(transfer_matrix_j)) + if ~np.isreal(poles[j]): # complex pole + transfer_matrix_j = np.hstack([np.real(transfer_matrix_j), + np.imag(transfer_matrix_j)]) + ker_pole.extend([ker_pole_j, ker_pole_j]) + + # Skip next pole as it is the conjugate + skip_conjugate = True + else: # real pole, nothing to do + ker_pole.append(ker_pole_j) + + if j == 0: + transfer_matrix = transfer_matrix_j + else: + transfer_matrix = np.hstack((transfer_matrix, transfer_matrix_j)) + + if rankB > 1: # otherwise there is nothing we can optimize + stop, cur_rtol, nb_iter = update_loop(ker_pole, transfer_matrix, + poles, B, maxiter, rtol) + if not stop and rtol > 0: + # if rtol<=0 the user has probably done that on purpose, + # don't annoy him + err_msg = ( + "Convergence was not reached after maxiter iterations.\n" + f"You asked for a tolerance of {rtol}, we got {cur_rtol}." + ) + warnings.warn(err_msg, stacklevel=2) + + # reconstruct transfer_matrix to match complex conjugate pairs, + # ie transfer_matrix_j/transfer_matrix_j+1 are + # Re(Complex_pole), Im(Complex_pole) now and will be Re-Im/Re+Im after + transfer_matrix = transfer_matrix.astype(complex) + idx = 0 + while idx < poles.shape[0]-1: + if ~np.isreal(poles[idx]): + rel = transfer_matrix[:, idx].copy() + img = transfer_matrix[:, idx+1] + # rel will be an array referencing a column of transfer_matrix + # if we don't copy() it will changer after the next line and + # and the line after will not yield the correct value + transfer_matrix[:, idx] = rel-1j*img + transfer_matrix[:, idx+1] = rel+1j*img + idx += 1 # skip next one + idx += 1 + + try: + m = np.linalg.solve(transfer_matrix.T, np.dot(np.diag(poles), + transfer_matrix.T)).T + gain_matrix = np.linalg.solve(z, np.dot(u0.T, m-A)) + except np.linalg.LinAlgError as e: + raise ValueError("The poles you've chosen can't be placed. " + "Check the controllability matrix and try " + "another set of poles") from e + + # Beware: Kautsky solves A+BK but the usual form is A-BK + gain_matrix = -gain_matrix + # K still contains complex with ~=0j imaginary parts, get rid of them + gain_matrix = np.real(gain_matrix) + + full_state_feedback = Bunch() + full_state_feedback.gain_matrix = gain_matrix + full_state_feedback.computed_poles = _order_complex_poles( + np.linalg.eig(A - np.dot(B, gain_matrix))[0] + ) + full_state_feedback.requested_poles = poles + full_state_feedback.X = transfer_matrix + full_state_feedback.rtol = cur_rtol + full_state_feedback.nb_iter = nb_iter + + return full_state_feedback + + +def dlsim(system, u, t=None, x0=None): + """ + Simulate output of a discrete-time linear system. + + Parameters + ---------- + system : tuple of array_like or instance of `dlti` + A tuple describing the system. + The following gives the number of elements in the tuple and + the interpretation: + + * 1: (instance of `dlti`) + * 3: (num, den, dt) + * 4: (zeros, poles, gain, dt) + * 5: (A, B, C, D, dt) + + u : array_like + An input array describing the input at each time `t` (interpolation is + assumed between given times). If there are multiple inputs, then each + column of the rank-2 array represents an input. + t : array_like, optional + The time steps at which the input is defined. If `t` is given, it + must be the same length as `u`, and the final value in `t` determines + the number of steps returned in the output. + x0 : array_like, optional + The initial conditions on the state vector (zero by default). + + Returns + ------- + tout : ndarray + Time values for the output, as a 1-D array. + yout : ndarray + System response, as a 1-D array. + xout : ndarray, optional + Time-evolution of the state-vector. Only generated if the input is a + `StateSpace` system. + + See Also + -------- + lsim, dstep, dimpulse, cont2discrete + + Examples + -------- + A simple integrator transfer function with a discrete time step of 1.0 + could be implemented as: + + >>> import numpy as np + >>> from scipy import signal + >>> tf = ([1.0,], [1.0, -1.0], 1.0) + >>> t_in = [0.0, 1.0, 2.0, 3.0] + >>> u = np.asarray([0.0, 0.0, 1.0, 1.0]) + >>> t_out, y = signal.dlsim(tf, u, t=t_in) + >>> y.T + array([[ 0., 0., 0., 1.]]) + + """ + # Convert system to dlti-StateSpace + if isinstance(system, lti): + raise AttributeError('dlsim can only be used with discrete-time dlti ' + 'systems.') + elif not isinstance(system, dlti): + system = dlti(*system[:-1], dt=system[-1]) + + # Condition needed to ensure output remains compatible + is_ss_input = isinstance(system, StateSpace) + system = system._as_ss() + + u = np.atleast_1d(u) + + if u.ndim == 1: + u = np.atleast_2d(u).T + + if t is None: + out_samples = len(u) + stoptime = (out_samples - 1) * system.dt + else: + stoptime = t[-1] + out_samples = int(np.floor(stoptime / system.dt)) + 1 + + # Pre-build output arrays + xout = np.zeros((out_samples, system.A.shape[0])) + yout = np.zeros((out_samples, system.C.shape[0])) + tout = np.linspace(0.0, stoptime, num=out_samples) + + # Check initial condition + if x0 is None: + xout[0, :] = np.zeros((system.A.shape[1],)) + else: + xout[0, :] = np.asarray(x0) + + # Pre-interpolate inputs into the desired time steps + if t is None: + u_dt = u + else: + if len(u.shape) == 1: + u = u[:, np.newaxis] + + u_dt = make_interp_spline(t, u, k=1)(tout) + + # Simulate the system + for i in range(0, out_samples - 1): + xout[i+1, :] = (np.dot(system.A, xout[i, :]) + + np.dot(system.B, u_dt[i, :])) + yout[i, :] = (np.dot(system.C, xout[i, :]) + + np.dot(system.D, u_dt[i, :])) + + # Last point + yout[out_samples-1, :] = (np.dot(system.C, xout[out_samples-1, :]) + + np.dot(system.D, u_dt[out_samples-1, :])) + + if is_ss_input: + return tout, yout, xout + else: + return tout, yout + + +def dimpulse(system, x0=None, t=None, n=None): + """ + Impulse response of discrete-time system. + + Parameters + ---------- + system : tuple of array_like or instance of `dlti` + A tuple describing the system. + The following gives the number of elements in the tuple and + the interpretation: + + * 1: (instance of `dlti`) + * 3: (num, den, dt) + * 4: (zeros, poles, gain, dt) + * 5: (A, B, C, D, dt) + + x0 : array_like, optional + Initial state-vector. Defaults to zero. + t : array_like, optional + Time points. Computed if not given. + n : int, optional + The number of time points to compute (if `t` is not given). + + Returns + ------- + tout : ndarray + Time values for the output, as a 1-D array. + yout : tuple of ndarray + Impulse response of system. Each element of the tuple represents + the output of the system based on an impulse in each input. + + See Also + -------- + impulse, dstep, dlsim, cont2discrete + + Examples + -------- + >>> import numpy as np + >>> from scipy import signal + >>> import matplotlib.pyplot as plt + + >>> butter = signal.dlti(*signal.butter(3, 0.5)) + >>> t, y = signal.dimpulse(butter, n=25) + >>> plt.step(t, np.squeeze(y)) + >>> plt.grid() + >>> plt.xlabel('n [samples]') + >>> plt.ylabel('Amplitude') + + """ + # Convert system to dlti-StateSpace + if isinstance(system, dlti): + system = system._as_ss() + elif isinstance(system, lti): + raise AttributeError('dimpulse can only be used with discrete-time ' + 'dlti systems.') + else: + system = dlti(*system[:-1], dt=system[-1])._as_ss() + + # Default to 100 samples if unspecified + if n is None: + n = 100 + + # If time is not specified, use the number of samples + # and system dt + if t is None: + t = np.linspace(0, n * system.dt, n, endpoint=False) + else: + t = np.asarray(t) + + # For each input, implement a step change + yout = None + for i in range(0, system.inputs): + u = np.zeros((t.shape[0], system.inputs)) + u[0, i] = 1.0 + + one_output = dlsim(system, u, t=t, x0=x0) + + if yout is None: + yout = (one_output[1],) + else: + yout = yout + (one_output[1],) + + tout = one_output[0] + + return tout, yout + + +def dstep(system, x0=None, t=None, n=None): + """ + Step response of discrete-time system. + + Parameters + ---------- + system : tuple of array_like + A tuple describing the system. + The following gives the number of elements in the tuple and + the interpretation: + + * 1: (instance of `dlti`) + * 3: (num, den, dt) + * 4: (zeros, poles, gain, dt) + * 5: (A, B, C, D, dt) + + x0 : array_like, optional + Initial state-vector. Defaults to zero. + t : array_like, optional + Time points. Computed if not given. + n : int, optional + The number of time points to compute (if `t` is not given). + + Returns + ------- + tout : ndarray + Output time points, as a 1-D array. + yout : tuple of ndarray + Step response of system. Each element of the tuple represents + the output of the system based on a step response to each input. + + See Also + -------- + step, dimpulse, dlsim, cont2discrete + + Examples + -------- + >>> import numpy as np + >>> from scipy import signal + >>> import matplotlib.pyplot as plt + + >>> butter = signal.dlti(*signal.butter(3, 0.5)) + >>> t, y = signal.dstep(butter, n=25) + >>> plt.step(t, np.squeeze(y)) + >>> plt.grid() + >>> plt.xlabel('n [samples]') + >>> plt.ylabel('Amplitude') + """ + # Convert system to dlti-StateSpace + if isinstance(system, dlti): + system = system._as_ss() + elif isinstance(system, lti): + raise AttributeError('dstep can only be used with discrete-time dlti ' + 'systems.') + else: + system = dlti(*system[:-1], dt=system[-1])._as_ss() + + # Default to 100 samples if unspecified + if n is None: + n = 100 + + # If time is not specified, use the number of samples + # and system dt + if t is None: + t = np.linspace(0, n * system.dt, n, endpoint=False) + else: + t = np.asarray(t) + + # For each input, implement a step change + yout = None + for i in range(0, system.inputs): + u = np.zeros((t.shape[0], system.inputs)) + u[:, i] = np.ones((t.shape[0],)) + + one_output = dlsim(system, u, t=t, x0=x0) + + if yout is None: + yout = (one_output[1],) + else: + yout = yout + (one_output[1],) + + tout = one_output[0] + + return tout, yout + + +def dfreqresp(system, w=None, n=10000, whole=False): + r""" + Calculate the frequency response of a discrete-time system. + + Parameters + ---------- + system : an instance of the `dlti` class or a tuple describing the system. + The following gives the number of elements in the tuple and + the interpretation: + + * 1 (instance of `dlti`) + * 2 (numerator, denominator, dt) + * 3 (zeros, poles, gain, dt) + * 4 (A, B, C, D, dt) + + w : array_like, optional + Array of frequencies (in radians/sample). Magnitude and phase data is + calculated for every value in this array. If not given a reasonable + set will be calculated. + n : int, optional + Number of frequency points to compute if `w` is not given. The `n` + frequencies are logarithmically spaced in an interval chosen to + include the influence of the poles and zeros of the system. + whole : bool, optional + Normally, if 'w' is not given, frequencies are computed from 0 to the + Nyquist frequency, pi radians/sample (upper-half of unit-circle). If + `whole` is True, compute frequencies from 0 to 2*pi radians/sample. + + Returns + ------- + w : 1D ndarray + Frequency array [radians/sample] + H : 1D ndarray + Array of complex magnitude values + + Notes + ----- + If (num, den) is passed in for ``system``, coefficients for both the + numerator and denominator should be specified in descending exponent + order (e.g. ``z^2 + 3z + 5`` would be represented as ``[1, 3, 5]``). + + .. versionadded:: 0.18.0 + + Examples + -------- + Generating the Nyquist plot of a transfer function + + >>> from scipy import signal + >>> import matplotlib.pyplot as plt + + Construct the transfer function + :math:`H(z) = \frac{1}{z^2 + 2z + 3}` with a sampling time of 0.05 + seconds: + + >>> sys = signal.TransferFunction([1], [1, 2, 3], dt=0.05) + + >>> w, H = signal.dfreqresp(sys) + + >>> plt.figure() + >>> plt.plot(H.real, H.imag, "b") + >>> plt.plot(H.real, -H.imag, "r") + >>> plt.show() + + """ + if not isinstance(system, dlti): + if isinstance(system, lti): + raise AttributeError('dfreqresp can only be used with ' + 'discrete-time systems.') + + system = dlti(*system[:-1], dt=system[-1]) + + if isinstance(system, StateSpace): + # No SS->ZPK code exists right now, just SS->TF->ZPK + system = system._as_tf() + + if not isinstance(system, (TransferFunction, ZerosPolesGain)): + raise ValueError('Unknown system type') + + if system.inputs != 1 or system.outputs != 1: + raise ValueError("dfreqresp requires a SISO (single input, single " + "output) system.") + + if w is not None: + worN = w + else: + worN = n + + if isinstance(system, TransferFunction): + # Convert numerator and denominator from polynomials in the variable + # 'z' to polynomials in the variable 'z^-1', as freqz expects. + num, den = TransferFunction._z_to_zinv(system.num.ravel(), system.den) + w, h = freqz(num, den, worN=worN, whole=whole) + + elif isinstance(system, ZerosPolesGain): + w, h = freqz_zpk(system.zeros, system.poles, system.gain, worN=worN, + whole=whole) + + return w, h + + +def dbode(system, w=None, n=100): + r""" + Calculate Bode magnitude and phase data of a discrete-time system. + + Parameters + ---------- + system : an instance of the LTI class or a tuple describing the system. + The following gives the number of elements in the tuple and + the interpretation: + + * 1 (instance of `dlti`) + * 2 (num, den, dt) + * 3 (zeros, poles, gain, dt) + * 4 (A, B, C, D, dt) + + w : array_like, optional + Array of frequencies (in radians/sample). Magnitude and phase data is + calculated for every value in this array. If not given a reasonable + set will be calculated. + n : int, optional + Number of frequency points to compute if `w` is not given. The `n` + frequencies are logarithmically spaced in an interval chosen to + include the influence of the poles and zeros of the system. + + Returns + ------- + w : 1D ndarray + Frequency array [rad/time_unit] + mag : 1D ndarray + Magnitude array [dB] + phase : 1D ndarray + Phase array [deg] + + Notes + ----- + If (num, den) is passed in for ``system``, coefficients for both the + numerator and denominator should be specified in descending exponent + order (e.g. ``z^2 + 3z + 5`` would be represented as ``[1, 3, 5]``). + + .. versionadded:: 0.18.0 + + Examples + -------- + >>> from scipy import signal + >>> import matplotlib.pyplot as plt + + Construct the transfer function :math:`H(z) = \frac{1}{z^2 + 2z + 3}` with + a sampling time of 0.05 seconds: + + >>> sys = signal.TransferFunction([1], [1, 2, 3], dt=0.05) + + Equivalent: sys.bode() + + >>> w, mag, phase = signal.dbode(sys) + + >>> plt.figure() + >>> plt.semilogx(w, mag) # Bode magnitude plot + >>> plt.figure() + >>> plt.semilogx(w, phase) # Bode phase plot + >>> plt.show() + + """ + w, y = dfreqresp(system, w=w, n=n) + + if isinstance(system, dlti): + dt = system.dt + else: + dt = system[-1] + + mag = 20.0 * numpy.log10(abs(y)) + phase = numpy.rad2deg(numpy.unwrap(numpy.angle(y))) + + return w / dt, mag, phase