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Fix negative real handling and improve pole matching logic #1216

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UbeenII wants to merge 6 commits into from
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Fix negative real handling and improve pole matching logic #1216

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8821978
2 fixes. 1st fix: the m_nr branch which is meant to handle negative r…
UbeenII May 16, 2026
287ce1a
Restore original continuous test target value to fix accidental edit
UbeenII Jun 7, 2026
a1d6f4e
Update control/tests/timeresp_test.py
UbeenII Jun 9, 2026
005eebf
Update control/timeresp.py
UbeenII Jun 9, 2026
0d03091
Clean up imports in timeresp_test.py
UbeenII Jun 9, 2026
b0f9e9e
Removed blank line
UbeenII Jun 9, 2026
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11 changes: 11 additions & 0 deletions control/tests/timeresp_test.py
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Original file line number Diff line number Diff line change
Expand Up @@ -6,13 +6,16 @@
import numpy as np
import pytest


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import control as ct
from control import StateSpace, TransferFunction, c2d, isctime, ss2tf, tf2ss
from control.exception import pandas_check
from control.timeresp import _default_time_vector, _ideal_tfinal_and_dt, \
forced_response, impulse_response, initial_response, step_info, \
step_response

import warnings
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@slivingston slivingston Jun 9, 2026

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I will remove these extra blank lines before merging. (Normally, only up to 2 blank lines are used to separate top-level blocks in a Python file.)

class TSys:
"""Struct of test system"""
Expand Down Expand Up @@ -826,6 +829,14 @@ def test_auto_generated_time_vector_tfinal(self, tfsys, tfinal):
np.testing.assert_allclose(ideal_tfinal, tfinal, rtol=1e-4)
T = _default_time_vector(tfsys)
np.testing.assert_allclose(T[-1], tfinal, atol=0.5*ideal_dt)

def test_discrete_time_negative_one_settling(self):
#system with -1 pole
TF = TransferFunction([1,3,0],[1,3,2], dt =True)
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with warnings.catch_warnings():
warnings.simplefilter("error")
impulse_response(TF)


@pytest.mark.parametrize("wn, zeta", [(10, 0), (100, 0), (100, .1)])
def test_auto_generated_time_vector_dt_cont1(self, wn, zeta):
Expand Down
3 changes: 2 additions & 1 deletion control/timeresp.py
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Expand Up @@ -2172,12 +2172,13 @@ 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(p.real+1)>sqrt_eps)
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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

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m_int = (p.real - 1 < sqrt_eps) & (np.abs(p.imag) < sqrt_eps)
p_int, p = p[m_int], p[~m_int]
# pure oscillatory modes
Expand Down
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