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fix _isstatic() to use nstates==0 #790

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Merged
merged 2 commits into from
Nov 16, 2022
Merged

fix _isstatic() to use nstates==0 #790

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c425d2c
fix _isstatic() to use nstates==0
murrayrm Nov 13, 2022
c82605b
Merge branch 'main' into fix_isstatic-12Nov2022
sawyerbfuller Nov 16, 2022
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10 changes: 2 additions & 8 deletions control/statesp.py
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Original file line number Diff line number Diff line change
Expand Up @@ -326,7 +326,7 @@ def __init__(self, *args, init_namedio=True, **kwargs):
D = np.zeros((C.shape[0], B.shape[1]))
D = _ssmatrix(D)

# Matrices definining the linear system
# Matrices defining the linear system
self.A = A
self.B = B
self.C = C
Expand All @@ -346,9 +346,8 @@ def __init__(self, *args, init_namedio=True, **kwargs):
defaults = args[0] if len(args) == 1 else \
{'inputs': D.shape[1], 'outputs': D.shape[0],
'states': A.shape[0]}
static = (A.size == 0)
name, inputs, outputs, states, dt = _process_namedio_keywords(
kwargs, defaults, static=static, end=True)
kwargs, defaults, static=(A.size == 0), end=True)

# Initialize LTI (NamedIOSystem) object
super().__init__(
Expand Down Expand Up @@ -1484,11 +1483,6 @@ def output(self, t, x, u=None, params=None):
return (self.C @ x).reshape((-1,)) \
+ (self.D @ u).reshape((-1,)) # return as row vector

def _isstatic(self):
"""True if and only if the system has no dynamics, that is,
if A and B are zero. """
return not np.any(self.A) and not np.any(self.B)


# TODO: add discrete time check
def _convert_to_statespace(sys):
Expand Down
10 changes: 9 additions & 1 deletion control/tests/iosys_test.py
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Expand Up @@ -41,6 +41,9 @@ class TSys:
[[-1, 1], [0, -2]], [[0, 1], [1, 0]],
[[1, 0], [0, 1]], np.zeros((2, 2)))

# Create a static gain linear system
T.staticgain = ct.StateSpace([], [], [], 1)

# Create simulation parameters
T.T = np.linspace(0, 10, 100)
T.U = np.sin(T.T)
Expand All @@ -51,7 +54,7 @@ class TSys:
def test_linear_iosys(self, tsys):
# Create an input/output system from the linear system
linsys = tsys.siso_linsys
iosys = ios.LinearIOSystem(linsys)
iosys = ios.LinearIOSystem(linsys).copy()
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is it obvious why this .copy is necessary?

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Definitely not obvious, but this gets rid of a warning later on since the interconnect function generates a warning if a system appears more than once in an interconnected system, since then the name of system is not unique. (It's also possible to turn the warning off with warn_dupicate=False).


# Make sure that the right hand side matches linear system
for x, u in (([0, 0], 0), ([1, 0], 0), ([0, 1], 0), ([0, 0], 1)):
Expand All @@ -66,6 +69,11 @@ def test_linear_iosys(self, tsys):
np.testing.assert_array_almost_equal(lti_t, ios_t)
np.testing.assert_allclose(lti_y, ios_y, atol=0.002, rtol=0.)

# Make sure that a static linear system has dt=None
# and otherwise dt is as specified
assert ios.LinearIOSystem(tsys.staticgain).dt is None
assert ios.LinearIOSystem(tsys.staticgain, dt=.1).dt == .1

def test_tf2io(self, tsys):
# Create a transfer function from the state space system
linsys = tsys.siso_linsys
Expand Down
34 changes: 14 additions & 20 deletions control/tests/statesp_test.py
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Expand Up @@ -399,25 +399,6 @@ def test_freq_resp(self):
mag, phase, omega = sys.freqresp(true_omega)
np.testing.assert_almost_equal(mag, true_mag)

def test__isstatic(self):
A0 = np.zeros((2,2))
A1 = A0.copy()
A1[0,1] = 1.1
B0 = np.zeros((2,1))
B1 = B0.copy()
B1[0,0] = 1.3
C0 = A0
C1 = np.eye(2)
D0 = 0
D1 = np.ones((2,1))
assert StateSpace(A0, B0, C1, D1)._isstatic()
assert not StateSpace(A1, B0, C1, D1)._isstatic()
assert not StateSpace(A0, B1, C1, D1)._isstatic()
assert not StateSpace(A1, B1, C1, D1)._isstatic()
assert StateSpace(A0, B0, C0, D0)._isstatic()
assert StateSpace(A0, B0, C0, D1)._isstatic()
assert StateSpace(A0, B0, C1, D0)._isstatic()

@slycotonly
def test_minreal(self):
"""Test a minreal model reduction."""
Expand Down Expand Up @@ -1160,6 +1141,20 @@ def test_linfnorm_ct_mimo(self, ct_siso):
np.testing.assert_allclose(fpeak, reffpeak)


@pytest.mark.parametrize("args, static", [
(([], [], [], 1), True), # ctime, empty state
(([], [], [], 1, 1), True), # dtime, empty state
((0, 0, 0, 1), False), # ctime, unused state
((-1, 0, 0, 1), False), # ctime, exponential decay
((-1, 0, 0, 0), False), # ctime, no input, no output
((0, 0, 0, 1, 1), False), # dtime, integrator
((1, 0, 0, 1, 1), False), # dtime, unused state
((0, 0, 0, 1, None), False), # unspecified, unused state
])
def test_isstatic(args, static):
sys = ct.StateSpace(*args)
assert sys._isstatic() == static

# Make sure that using params for StateSpace objects generates a warning
def test_params_warning():
sys = StateSpace(-1, 1, 1, 0)
Expand All @@ -1169,4 +1164,3 @@ def test_params_warning():

with pytest.warns(UserWarning, match="params keyword ignored"):
sys.output(0, [0], [0], {'k': 5})