8000 Fix namespace and logic errrors in statesp.freqresp + unit tests · MaxGaukler/python-control@057c5ca · GitHub
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Fix namespace and logic errrors in statesp.freqresp + unit tests
As pointed out in PR python-control#192, there were some namespace errors in the statesp module related to checking whether the frequency range as valid for discrete time systems. I added a unit test that covered this code (and exposed the error) and fixed up the namespace problems (as in PR python-control#192). There was also a logic error in the way that frequencies were checked and the warning message referred to the wrong function.
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‎control/statesp.py

Lines changed: 2 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -460,10 +460,8 @@ def freqresp(self, omega):
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if isdtime(self, strict=True):
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dt = timebase(self)
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cmplx_freqs = exp(1.j * omega * dt)
463-
if ((omega * dt).any() > pi):
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warn_message = ("evalfr: frequency evaluation"
465-
" above Nyquist frequency")
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warnings.warn(warn_message)
463+
if (max(omega) * dt > math.pi):
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warn("freqresp: frequency evaluation above Nyquist frequency")
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else:
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cmplx_freqs = omega * 1.j
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‎control/tests/freqresp_test.py

Lines changed: 62 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -10,7 +10,8 @@
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import numpy as np
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import control as ctrl
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from control.statesp import StateSpace
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from control.matlab import ss, tf, bode
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from control.xferfcn import TransferFunction
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from control.matlab import ss, tf, bode, rss
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from control.exception import slycot_check
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import matplotlib.pyplot as plt
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@@ -107,6 +108,66 @@ def test_mimo(self):
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#plt.figure(4)
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#bode(sysMIMO,self.omega)
109110

111+
def test_discrete(self):
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# Test discrete time frequency response
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# SISO state space systems with either fixed or unspecified sampling times
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sys = rss(3, 1, 1)
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siso_ss1d = StateSpace(sys.A, sys.B, sys.C, sys.D, 0.1)
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siso_ss2d = StateSpace(sys.A, sys.B, sys.C, sys.D, True)
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# MIMO state space systems with either fixed or unspecified sampling times
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A = [[-3., 4., 2.], [-1., -3., 0.], [2., 5., 3.]]
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B = [[1., 4.], [-3., -3.], [-2., 1.]]
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C = [[4., 2., -3.], [1., 4., 3.]]
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D = [[-2., 4.], [0., 1.]]
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mimo_ss1d = StateSpace(A, B, C, D, 0.1)
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mimo_ss2d = StateSpace(A, B, C, D, True)
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# SISO transfer functions
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siso_tf1d = TransferFunction([1, 1], [1, 2, 1], 0.1)
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siso_tf2d = TransferFunction([1, 1], [1, 2, 1], True)
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# Go through each system and call the code, checking return types
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for sys in (siso_ss1d, siso_ss2d, mimo_ss1d, mimo_ss2d,
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siso_tf1d, siso_tf2d):
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# Set frequency range to just below Nyquist freq (for Bode)
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omega_ok = np.linspace(10e-4,0.99,100) * np.pi/sys.dt
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# Test frequency response
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ret = sys.freqresp(omega_ok)
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140+
# Check for warning if frequency is out of range
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import warnings
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with warnings.catch_warnings(record=True) as w:
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omega_bad = np.linspace(10e-4,1.1,10) * np.pi/sys.dt
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ret = sys.freqresp(omega_bad)
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print("len(w) =", len(w))
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assert len(w) == 1
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assert "above" in str(w[-1].message)
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assert "Nyquist" in str(w[-1].message)
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# Test bode plots (currently only implemented for SISO)
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if (sys.inputs == 1 and sys.outputs == 1):
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# Generic call (frequency range calculated automatically)
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ret_ss = bode(sys)
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# Convert to transfer function and test bode again
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systf = tf(sys);
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ret_tf = bode(systf)
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# Make sure we can pass a frequency range
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bode(sys, omega_ok)
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else:
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# Calling bode should generate a not implemented error
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try:
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ret_ss = bode(sys)
166+
raise RuntimeError("MIMO bode seems to be implemented?")
167+
except NotImplementedError:
168+
# This is where we should end up (so do nothing)
169+
continue
170+
110171
def suite():
111172
return unittest.TestLoader().loadTestsFromTestCase(TestTimeresp)
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