fix: HinfSyn Bk sign + 105 hardening tests from python-control audit#25
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fix: HinfSyn Bk sign + 105 hardening tests from python-control audit#25
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The observer gain L is stored with negative sign convention:
L = -(Y*C2' + S2)*R2^{-1}. The DGKF central controller requires
Bk = -Zp*L to get positive observer correction, but the code had
Bk = Zp*L — missing the negation.
This produced controllers with unstable closed-loop poles for plants
with open-loop RHP eigenvalues (e.g., Scherer et al. IEEE TAC 1997
Example 7). Previously tested stable plants masked the sign error.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Systematic audit of python-control issues (100+), PRs (40+), test suites, Jupyter notebooks (14), and example scripts (17) to extract edge cases, MATLAB-validated vectors, and numerical pitfalls. Tests organized by functional area: - hardening_test.go: Riccati, LQR/LQE, symmetry, cross-terms (22) - hardening_placement_test.go: Acker, Place, Ctrb duality (10) - hardening_feedback_test.go: Feedback, Series, Parallel, TF (11) - hardening_gramian_test.go: MATLAB Gramians, HSV, H2/Hinf norms (13) - hardening_response_test.go: Step, impulse, DC gain, c2d (10) - hardening_lyapcanon_test.go: Lyapunov, modal/companion forms (13) - hardening_margin_test.go: GM/PM, phase unwrap, DT margins (12) - hardening_synthesis_test.go: Scherer H2 (norm=7.7484), PVTOL (5) - hardening_robust_test.go: Disk margins, Type 2/3, bandwidth (9) Key reference systems: PVTOL aircraft (6-state MIMO), Scherer et al. IEEE TAC 1997 (published H2 norm), Skogestad mixed-sensitivity, coupled spring-mass (transmission zero), inverted pendulum. python-control-audit.md documents all findings with test vectors. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Summary
Bkwas missing negation, producing unstable closed-loop poles for plants with RHP eigenvaluesBug fix
hinfsyn.go:156— The DGKF central controller requiresBk = -Zp*L(observer gainLis stored with negative convention), but code hadBk = Zp*L. This masked itself on stable plants but failed on the Scherer et al. (IEEE TAC 1997) benchmark with open-loop poles at1.69±2.50j.New tests by area
hardening_test.gohardening_placement_test.gohardening_feedback_test.gohardening_gramian_test.gohardening_response_test.gohardening_lyapcanon_test.gohardening_margin_test.gohardening_synthesis_test.gohardening_robust_test.goKey reference systems
Test plan
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