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GeezerVison is showing github.com — Fix bug in matched transformation + address other issues in #950 by murrayrm · Pull Request #951 · python-control/python-control

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@murrayrm

@murrayrm murrayrm commented Dec 26, 2023

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This PR fixes the calculation of the DC gain in the 'matched' transformation from continuous time to discrete time. It also fixes some other issues identified in #950. Also adds unit test for sample_system that catches the original error.

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@murrayrm
fix bug in matched transformation + address other issues in python-co…
3fb1a51 
…ntrol#950
@murrayrm murrayrm linked an issue Dec 26, 2023 that may be closed by this pull request
gain offset using control.matlab.c2d using method='matched' ? #950
Closed
@murrayrm murrayrm mentioned this pull request Dec 26, 2023
gain offset using control.matlab.c2d using method='matched' ? #950
Closed
@coveralls

coveralls commented Dec 26, 2023 •
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Coverage Status

coverage: 94.989% (-0.02%) from 95.009%
when pulling e4bcec0 on murrayrm:matched_bug-26Dec2023
into 7a8581c on python-control:main.
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sawyerbfuller
sawyerbfuller reviewed Dec 26, 2023
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Comment thread control/xferfcn.py Resolved

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murrayrm and others added 2 commits December 26, 2023 11:11
@murrayrm @sawyerbfuller
Update control/xferfcn.py
d4525a1 
Co-authored-by: Sawyer Fuller <[email protected]>
@murrayrm
fixed botched pathc from github
e4bcec0
@murrayrm
murrayrm merged commit 177d8b6 into python-control:main Dec 26, 2023
@murrayrm
murrayrm deleted the matched_bug-26Dec2023 branch December 26, 2023 19:32
@murrayrm murrayrm added this to the 0.10.0 milestone Mar 31, 2024
@binggao1230 binggao1230 mentioned this pull request Jul 21, 2026
Fix matched c2d/sample returning NaN for a pole or zero at the origin #1241
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binggao1230 added a commit to binggao1230/python-control that referenced this pull request Aug 9, 2026
@binggao1230
Fix matched c2d NaN for a pole or zero at the origin
f80d990 
TransferFunction.sample(Ts, method='matched') (and c2d) returned an
all-NaN numerator for any system with a pole or zero at s = 0 -
integrators, PI/PID controllers, differentiators and other type-1/2
systems.  The DC-gain match divides the continuous DC gain (inf for an
origin pole, 0 for an origin zero) by a zgain that carries the same
vanishing 1 - z factor, so the gain is 0/0 or inf/inf.

Match the gain from the non-origin factors only and restore the origin
scaling analytically through the z - 1 ~ s*Ts limit, which recovers the
textbook Ts/(z - 1) for 1/s, Ts**2/(z - 1)**2 for 1/s**2, and so on.
Finite-DC systems are byte-for-byte unchanged.  Completes the gain fix
from python-control#950/python-control#951.
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@murrayrm @coveralls @sawyerbfuller
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