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fix computation of default response time for constant systems #383

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merged 2 commits into from
May 17, 2020
Merged

fix computation of default response time for constant systems #383

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4bad487
fix computation of default response time for constant systems
murrayrm Mar 22, 2020
98f13be
add single function to compute response times
murrayrm Mar 24, 2020
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14 changes: 13 additions & 1 deletion control/tests/timeresp_test.py
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Original file line number Diff line number Diff line change
Expand Up @@ -94,9 +94,21 @@ def test_step_response(self):
np.testing.assert_array_equal(Tc.shape, Td.shape)
np.testing.assert_array_equal(youtc.shape, youtd.shape)

# Recreate issue #374 ("Bug in step_response()")
def test_step_nostates(self):
# Continuous time, constant system
sys = TransferFunction([1], [1])
t, y = step_response(sys)
np.testing.assert_array_equal(y, np.ones(len(t)))

# Discrete time, constant system
sys = TransferFunction([1], [1], 1)
t, y = step_response(sys)
np.testing.assert_array_equal(y, np.ones(len(t)))

def test_step_info(self):
# From matlab docs:
sys = TransferFunction([1,5,5],[1,1.65,5,6.5,2])
sys = TransferFunction([1, 5, 5], [1, 1.65, 5, 6.5, 2])
Strue = {
'RiseTime': 3.8456,
'SettlingTime': 27.9762,
Expand Down
50 changes: 24 additions & 26 deletions control/timeresp.py
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Original file line number Diff line number Diff line change
Expand Up @@ -512,13 +512,7 @@ def step_response(sys, T=None, X0=0., input=None, output=None,
"""
sys = _get_ss_simo(sys, input, output)
if T is None:
if isctime(sys):
T = _default_response_times(sys.A, 100)
else:
# For discrete time, use integers
tvec = _default_response_times(sys.A, 100)
T = range(int(np.ceil(max(tvec))))

T = _get_response_times(sys, N=100)
U = np.ones_like(T)

T, yout, xout = forced_response(sys, T, U, X0, transpose=transpose,
Expand Down Expand Up @@ -573,12 +567,7 @@ def step_info(sys, T=None, SettlingTimeThreshold=0.02,
'''
sys = _get_ss_simo(sys)
if T is None:
if isctime(sys):
T = _default_response_times(sys.A, 1000)
else:
# For discrete time, use integers
tvec = _default_response_times(sys.A, 1000)
T = range(int(np.ceil(max(tvec))))
T = _get_response_times(sys, N=1000)

T, yout = step_response(sys, T)

Expand Down Expand Up @@ -697,12 +686,8 @@ def initial_response(sys, T=None, X0=0., input=0, output=None,
# Create time and input vectors; checking is done in forced_response(...)
# The initial vector X0 is created in forced_response(...) if necessary
if T is None:
if isctime(sys):
T = _default_response_times(sys.A, 1000)
else:
# For discrete time, use integers
tvec = _default_response_times(sys.A, 1000)
T = range(int(np.ceil(max(tvec))))
# TODO: default step size inconsistent with step/impulse_response()
T = _get_response_times(sys, N=1000)
U = np.zeros_like(T)

T, yout, _xout = forced_response(sys, T, U, X0, transpose=transpose,
Expand Down Expand Up @@ -801,13 +786,7 @@ def impulse_response(sys, T=None, X0=0., input=0, output=None,

# Compute T and U, no checks necessary, they will be checked in lsim
if T is None:
if isctime(sys):
T = _default_response_times(sys.A, 100)
else:
# For discrete time, use integers
tvec = _default_response_times(sys.A, 100)
T = range(int(np.ceil(max(tvec))))

T = _get_response_times(sys, N=100)
U = np.zeros_like(T)

# Compute new X0 that contains the impulse
Expand All @@ -828,3 +807,22 @@ def impulse_response(sys, T=None, X0=0., input=0, output=None,
return T, yout, _xout

return T, yout


# Utility function to get response times
def _get_response_times(sys, N=100):
if isctime(sys):
if sys.A.shape == (0, 0):
# No dynamics; use the unit time interval
T = np.linspace(0, 1, N, endpoint=False)
else:
T = _default_response_times(sys.A, N)
else:
# For discrete time, use integers
if sys.A.shape == (0, 0):
# No dynamics; use N time steps
T = range(N)
else:
tvec = _default_response_times(sys.A, N)
T = range(int(np.ceil(max(tvec))))
return T