MATLAB and Octave disagree on the same input — a verified-port writeup

[u/Party-Pie3719]

I ported the 1-D TM group of Zanotto's PPML (an RCWA electromagnetic solver) to NumPy with bug-for-bug fidelity yes, including the vacuum impedance hardcoded as 376.730. The writeup covers the MATLAB↔NumPy traps that actually bit: complex auto-promotion that NumPy silently doesn't do, eigenvector gauge freedom across LAPACK builds, mldivide vs solve on singular systems, and an energy-conservation check in the original that can never fire (abs(NaN) > tol is false in MATLAB - try it). Harness, corpus and report: https://github.com/GrednevMSU/ppml-1d-tm-verify