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fix damp method for discrete time systems with a negative real-valued pole #647

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Merged
merged 2 commits into from
Aug 19, 2021
Merged

fix damp method for discrete time systems with a negative real-valued pole #647

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78b6fc2
fix the return of the damp method for discrete time systems with a ne…
vincentchoqueuse Aug 17, 2021
140ca08
fix PEP8 compliance style and preserve pole type
vincentchoqueuse Aug 18, 2021
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2 changes: 1 addition & 1 deletion control/lti.py
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Original file line number Diff line number Diff line change
Expand Up @@ -159,7 +159,7 @@ def damp(self):
poles = self.pole()

if isdtime(self, strict=True):
splane_poles = np.log(poles)/self.dt
splane_poles = np.log(poles.astype(complex))/self.dt
else:
splane_poles = poles
wn = absolute(splane_poles)
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8 changes: 8 additions & 0 deletions control/tests/lti_test.py
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Expand Up @@ -70,6 +70,14 @@ def test_damp(self):
np.testing.assert_almost_equal(sys_dt.damp(), expected_dt)
np.testing.assert_almost_equal(damp(sys_dt), expected_dt)

#also check that for a discrete system with a negative real pole the damp function can extract wn and zeta.
p2_zplane = -0.2
sys_dt2 = tf(1, [1, -p2_zplane], dt)
wn2, zeta2, p2 = sys_dt2.damp()
p2_splane = -wn2 * zeta2 + 1j * wn2 * np.sqrt(1 - zeta2**2)
p2_zplane = np.exp(p2_splane * dt)
np.testing.assert_almost_equal(p2, p2_zplane)

def test_dcgain(self):
sys = tf(84, [1, 2])
np.testing.assert_allclose(sys.dcgain(), 42)
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