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fix(timeresp): avoid warning for discrete -1 poles #1225

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marko1olo wants to merge 1 commit into from
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fix(timeresp): avoid warning for discrete -1 poles #1225

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21 changes: 21 additions & 0 deletions control/tests/timeresp_test.py
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Original file line number Diff line number Diff line change
@@ -1,5 +1,6 @@
"""timeresp_test.py - test time response functions"""

import warnings
from copy import copy
from math import isclose

Expand Down Expand Up @@ -582,6 +583,17 @@ def test_discrete_time_impulse_input(self):

np.testing.assert_array_equal(response.inputs,Uexpected)

def test_discrete_time_impulse_negative_poles_no_warning(self):
# A negative pole on the unit circle should be treated as oscillatory.
sysd = ct.TransferFunction([1, 3, 0], [1, 3, 2], dt=True)

with warnings.catch_warnings():
warnings.simplefilter("error", RuntimeWarning)
response = ct.impulse_response(sysd, 5)

np.testing.assert_allclose(response.time, np.arange(6))
assert np.all(np.isfinite(response.outputs))

@pytest.mark.parametrize("tsystem", ["siso_ss1"], indirect=True)
def test_impulse_response_warnD(self, tsystem):
"""Test warning about direct feedthrough"""
Expand Down Expand Up @@ -827,6 +839,15 @@ def test_auto_generated_time_vector_tfinal(self, tfsys, tfinal):
T = _default_time_vector(tfsys)
np.testing.assert_allclose(T[-1], tfinal, atol=0.5*ideal_dt)

@pytest.mark.parametrize(
"tfsys, tfinal",
[(TransferFunction(1, [1, .5], dt=True), 9.96578), # pole at -0.5
(TransferFunction(1, [1, 1], dt=True), 10)]) # pole at -1
def test_discrete_negative_real_pole_tfinal(self, tfsys, tfinal):
"""Confirm discrete negative real pole time horizon estimates."""
ideal_tfinal, _ = _ideal_tfinal_and_dt(tfsys)
np.testing.assert_allclose(ideal_tfinal, tfinal, rtol=1e-4)

@pytest.mark.parametrize("wn, zeta", [(10, 0), (100, 0), (100, .1)])
def test_auto_generated_time_vector_dt_cont1(self, wn, zeta):
"""Confirm a TF with a natural frequency of wn rad/s gets a
Expand Down
8 changes: 6 additions & 2 deletions control/timeresp.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2172,13 +2172,17 @@ def _ideal_tfinal_and_dt(sys, is_step=True):
m_z = np.abs(p) < sqrt_eps
p = p[~m_z]
# Negative reals- treated as oscillatory mode
m_nr = (p.real < 0) & (np.abs(p.imag) < sqrt_eps)
m_nr = (
(p.real < 0) & (np.abs(p.imag) < sqrt_eps) &
(np.abs(np.abs(p) - 1) >= sqrt_eps))
p_nr, p = p[m_nr], p[~m_nr]
if p_nr.size > 0:
t_emp = np.max(log_decay_percent / np.abs((np.log(p_nr)/dt).real))
tfinal = max(tfinal, t_emp)
# discrete integrators
m_int = (p.real - 1 < sqrt_eps) & (np.abs(p.imag) < sqrt_eps)
m_int = (
(p.real > 0) & (p.real - 1 < sqrt_eps) &
(np.abs(p.imag) < sqrt_eps))
p_int, p = p[m_int], p[~m_int]
# pure oscillatory modes
m_w = (np.abs(np.abs(p) - 1) < sqrt_eps)
Expand Down