Fix pid_tf coefficients for Ki=0 with first-order derivative filter#1058
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For Kp + Kd*s/(Tf*s+1) the numerator polynomial is ((Kp*Tf + Kd)*s + Kp), but the code was using [Kd*Tf + Kd, Kd] — Kp dropped entirely and replaced by Kd. The returned transfer function therefore did not contain the proportional term. The other branches in the same function (Ki!=0/filter_order=1 on the next line) use the correct form, which this brings into line. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## master #1058 +/- ##
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+ Coverage 91.61% 91.64% +0.02%
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Files 42 42
Lines 5653 5659 +6
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+ Hits 5179 5186 +7
+ Misses 474 473 -1 ☔ View full report in Codecov by Sentry. 🚀 New features to boost your workflow:
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Cross-check the transfer-function PID controller against the state-space realization, and against the analytical numerator [Kp*Tf+Kd, Kp]. On master both checks failed because the implementation emitted [Kd*Tf+Kd, Kd] (Kp dropped and replaced with Kd). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Summary
For
pid_tfwithKi = 0, first-order derivative filter, and a non-nothingTf, the returned transfer function should bei.e. numerator
[Kp*Tf + Kd, Kp]. The code instead produced[Kd*Tf + Kd, Kd]—Kpwas dropped entirely and substituted withKd. The returned controller therefore contained no proportional term.The adjacent branch (
Ki != 0,filter_order == 1) uses the correct form[Kd + Kp*Tf, Ki*Tf + Kp, Ki]; collapsing that forKi = 0agrees with the fix.Test plan
pid_tf(Kp, 0, Kd; Tf, filter_order=1)against the analytical transfer function above (Kp=2, Kd=0.5, Tf=0.1).test_pid_design.jlstill pass.🤖 Generated with Claude Code