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Dec 29, 2020
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Extend returnScipySignalLTI() to discrete systems #445

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45 changes: 37 additions & 8 deletions control/statesp.py
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Original file line number Diff line number Diff line change
Expand Up @@ -59,7 +59,8 @@
from numpy.linalg import solve, eigvals, matrix_rank
from numpy.linalg.linalg import LinAlgError
import scipy as sp
from scipy.signal import lti, cont2discrete
from scipy.signal import cont2discrete
from scipy.signal import StateSpace as signalStateSpace
from warnings import warn
from .lti import LTI, timebase, timebaseEqual, isdtime
from . import config
Expand Down Expand Up @@ -200,7 +201,7 @@ def __init__(self, *args, **kw):
raise ValueError("Needs 1 or 4 arguments; received %i." % len(args))

# Process keyword arguments
remove_useless = kw.get('remove_useless',
remove_useless = kw.get('remove_useless',
config.defaults['statesp.remove_useless_states'])

# Convert all matrices to standard form
Expand Down Expand Up @@ -798,9 +799,7 @@ def minreal(self, tol=0.0):
else:
return StateSpace(self)


# TODO: add discrete time check
def returnScipySignalLTI(self):
def returnScipySignalLTI(self, strict=True):
"""Return a list of a list of :class:`scipy.signal.lti` objects.

For instance,
Expand All @@ -809,15 +808,45 @@ def returnScipySignalLTI(self):
>>> out[3][5]

is a :class:`scipy.signal.lti` object corresponding to the transfer
function from the 6th input to the 4th output."""
function from the 6th input to the 4th output.

Parameters
----------
strict : bool, optional
True (default):
The timebase `ssobject.dt` cannot be None; it must
be continuous (0) or discrete (True or > 0).
False:
If `ssobject.dt` is None, continuous time
:class:`scipy.signal.lti` objects are returned.

Returns
-------
out : list of list of :class:`scipy.signal.StateSpace`
continuous time (inheriting from :class:`scipy.signal.lti`)
or discrete time (inheriting from :class:`scipy.signal.dlti`)
SISO objects
"""
if strict and self.dt is None:
raise ValueError("with strict=True, dt cannot be None")

if self.dt:
kwdt = {'dt': self.dt}
else:
# scipy convention for continuous time lti systems: call without
# dt keyword argument
kwdt = {}

# Preallocate the output.
out = [[[] for _ in range(self.inputs)] for _ in range(self.outputs)]

for i in range(self.outputs):
for j in range(self.inputs):
out[i][j] = lti(asarray(self.A), asarray(self.B[:, j]),
asarray(self.C[i, :]), self.D[i, j])
out[i][j] = signalStateSpace(asarray(self.A),
asarray(self.B[:, j:j + 1]),
asarray(self.C[i:i + 1, :]),
asarray(self.D[i:i + 1, j:j + 1]),
**kwdt)

return out

Expand Down
52 changes: 52 additions & 0 deletions control/tests/statesp_matrix_test.py
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Expand Up @@ -5,6 +5,7 @@

import unittest
import numpy as np
import pytest
from numpy.linalg import solve
from scipy.linalg import eigvals, block_diag
from control import matlab
Expand Down Expand Up @@ -673,5 +674,56 @@ def test_sample_system_prewarping(self):
decimal=4)


class TestLTIConverter:
"""Test returnScipySignalLTI method"""

@pytest.fixture
def mimoss(self, request):
"""Test system with various dt values"""
n = 5
m = 3
p = 2
bx, bu = np.mgrid[1:n + 1, 1:m + 1]
cy, cx = np.mgrid[1:p + 1, 1:n + 1]
dy, du = np.mgrid[1:p + 1, 1:m + 1]
return StateSpace(np.eye(5) + np.eye(5, 5, 1),
bx * bu,
cy * cx,
dy * du,
request.param)

@pytest.mark.parametrize("mimoss",
[None,
0,
0.1,
1,
True],
indirect=True)
def test_returnScipySignalLTI(self, mimoss):
"""Test returnScipySignalLTI method with strict=False"""
sslti = mimoss.returnScipySignalLTI(strict=False)
for i in range(mimoss.outputs):
for j in range(mimoss.inputs):
np.testing.assert_allclose(sslti[i][j].A, mimoss.A)
np.testing.assert_allclose(sslti[i][j].B, mimoss.B[:,
j:j + 1])
np.testing.assert_allclose(sslti[i][j].C, mimoss.C[i:i + 1,
:])
np.testing.assert_allclose(sslti[i][j].D, mimoss.D[i:i + 1,
j:j + 1])
if mimoss.dt == 0:
assert sslti[i][j].dt is None
else:
assert sslti[i][j].dt == mimoss.dt

@pytest.mark.parametrize("mimoss", [None], indirect=True)
def test_returnScipySignalLTI_error(self, mimoss):
"""Test returnScipySignalLTI method with dt=None and strict=True"""
with pytest.raises(ValueError):
mimoss.returnScipySignalLTI()
with pytest.raises(ValueError):
mimoss.returnScipySignalLTI(strict=True)


if __name__ == "__main__":
unittest.main()
41 changes: 41 additions & 0 deletions control/tests/xferfcn_test.py
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,8 @@
# RMM, 30 Mar 2011 (based on TestXferFcn from v0.4a)

import unittest
import pytest

import sys as pysys
import numpy as np
from control.statesp import StateSpace, _convertToStateSpace, rss
Expand Down Expand Up @@ -934,5 +936,44 @@ def test_sample_system_prewarping(self):
decimal=4)


class TestLTIConverter:
"""Test returnScipySignalLTI method"""

@pytest.fixture
def mimotf(self, request):
"""Test system with various dt values"""
return TransferFunction([[[11], [12], [13]],
[[21], [22], [23]]],
[[[1, -1]] * 3] * 2,
request.param)

@pytest.mark.parametrize("mimotf",
[None,
0,
0.1,
1,
True],
indirect=True)
def test_returnScipySignalLTI(self, mimotf):
"""Test returnScipySignalLTI method with strict=False"""
sslti = mimotf.returnScipySignalLTI(strict=False)
for i in range(2):
for j in range(3):
np.testing.assert_allclose(sslti[i][j].num, mimotf.num[i][j])
np.testing.assert_allclose(sslti[i][j].den, mimotf.den[i][j])
if mimotf.dt == 0:
assert sslti[i][j].dt is None
else:
assert sslti[i][j].dt == mimotf.dt

@pytest.mark.parametrize("mimotf", [None], indirect=True)
def test_returnScipySignalLTI_error(self, mimotf):
"""Test returnScipySignalLTI method with dt=None and strict=True"""
with pytest.raises(ValueError):
mimotf.returnScipySignalLTI()
with pytest.raises(ValueError):
mimotf.returnScipySignalLTI(strict=True)


if __name__ == "__main__":
unittest.main()
39 changes: 31 additions & 8 deletions control/xferfcn.py
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Original file line number Diff line number Diff line change
Expand Up @@ -57,7 +57,8 @@
polyadd, polymul, polyval, roots, sqrt, zeros, squeeze, exp, pi, \
where, delete, real, poly, nonzero
import scipy as sp
from scipy.signal import lti, tf2zpk, zpk2tf, cont2discrete
from scipy.signal import tf2zpk, zpk2tf, cont2discrete
from scipy.signal import TransferFunction as signalTransferFunction
from copy import deepcopy
from warnings import warn
from itertools import chain
Expand Down Expand Up @@ -801,30 +802,52 @@ def minreal(self, tol=None):
# end result
return TransferFunction(num, den, self.dt)

def returnScipySignalLTI(self):
def returnScipySignalLTI(self, strict=True):
"""Return a list of a list of :class:`scipy.signal.lti` objects.

For instance,

>>> out = tfobject.returnScipySignalLTI()
>>> out[3][5]

is a class:`scipy.signal.lti` object corresponding to the
is a :class:`scipy.signal.lti` object corresponding to the
transfer function from the 6th input to the 4th output.

Parameters
----------
strict : bool, optional
True (default):
The timebase `tfobject.dt` cannot be None; it must be
continuous (0) or discrete (True or > 0).
False:
if `tfobject.dt` is None, continuous time
:class:`scipy.signal.lti`objects are returned

Returns
-------
out : list of list of :class:`scipy.signal.TransferFunction`
continuous time (inheriting from :class:`scipy.signal.lti`)
or discrete time (inheriting from :class:`scipy.signal.dlti`)
SISO objects
"""
if strict and self.dt is None:
raise ValueError("with strict=True, dt cannot be None")

# TODO: implement for discrete time systems
if self.dt != 0 and self.dt is not None:
raise NotImplementedError("Function not \
implemented in discrete time")
if self.dt:
kwdt = {'dt': self.dt}
else:
# scipy convention for continuous time lti systems: call without
# dt keyword argument
kwdt = {}

# Preallocate the output.
out = [[[] for j in range(self.inputs)] for i in range(self.outputs)]

for i in range(self.outputs):
for j in range(self.inputs):
out[i][j] = lti(self.num[i][j], self.den[i][j])
out[i][j] = signalTransferFunction(self.num[i][j],
self.den[i][j],
**kwdt)

return out

Expand Down