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Add test for Nyquist evaluation at a pole #1104

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Merged
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Jan 29, 2025
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Add test for Nyquist evaluation at a pole #1104

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6 changes: 6 additions & 0 deletions control/freqplot.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1447,6 +1447,12 @@ def nyquist_response(
else:
contour = np.exp(splane_contour * sys.dt)

# Make sure we don't try to evaluate at a pole
if isinstance(sys, (StateSpace, TransferFunction)):
if any([pole in contour for pole in sys.poles()]):
raise RuntimeError(
"attempt to evaluate at a pole; indent required")

# Compute the primary curve
resp = sys(contour)

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9 changes: 9 additions & 0 deletions control/tests/nyquist_test.py
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Expand Up @@ -517,6 +517,15 @@ def test_nyquist_frd():
warnings.resetwarnings()


def test_no_indent_pole():
s = ct.tf('s')
sys = ((1 + 5/s)/(1 + 0.5/s))**2 # Double-Lag-Compensator

with pytest.raises(RuntimeError, match="evaluate at a pole"):
resp = ct.nyquist_response(
sys, warn_encirclements=False, indent_direction='none')


if __name__ == "__main__":
#
# Interactive mode: generate plots for manual viewing
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