Lifts the 27 `#[ignore]` markers on rtx-cfd and rtx-fea. 21 of them fail;
6 were stale, marking components that have since been implemented. The
suite now reports the truth, which means it is red.
The eigensolver had three independent defects, each individually fatal.
Found by writing closed-form tests first and confirming red:
- The generalized reduction formed M^-1 K and ran Lanczos on it.
M^-1 K has the right eigenvalues but is not symmetric even when K
and M both are, and Lanczos assumes symmetry -- so it returned a
wrong answer rather than an inaccurate one. On a 2-DOF spring-mass
chain with M = diag(2,1) it gave 1.633 against an exact root of
1 - sqrt(2)/2 ~= 0.293. Replaced with the Cholesky reduction
B = L^-1 (K - sigma M) L^-T.
- Output was unsorted. nalgebra's symmetric_eigen gives no ordering
guarantee and none was imposed; modal analysis names modes by index,
so the ordering is part of the contract.
- Eigenvectors could not be transformed back out of the Krylov basis.
The Lanczos block was (n x num_iter) and the tridiagonal
eigenvectors (min(num_iter, k) x k); whenever those differed the
multiply panicked on a dimension mismatch -- that is, on every
problem with more DOFs than requested modes, which is every real
modal analysis.
Lanczos now runs shift-invert by default. Plain Lanczos converges to the
eigenvalues of largest magnitude and modal analysis wants the lowest, so
without it the solver returns the modes nobody asked for. Also switched
to full reorthogonalization, twice per step, so converged eigenvalues do
not reappear as ghosts indistinguishable from genuine repeated roots.
ModalResults computed f = sqrt(lambda / 2pi) instead of
sqrt(lambda) / 2pi. The two agree only at lambda = 2pi, so a smoke test
asserting a positive frequency would never separate them. A
`#[cfg(disabled)]` module in the same file asserted the correct formula
-- the module was disabled rather than the bug fixed. That module is
removed; tests/eigenvalue_closed_form.rs supersedes it with every
expected value derived analytically.
Corrected a fixture rather than loosening its tolerance:
implementation_tests expected the smallest eigenvalue of
tridiag(-1, 4, -1) at order 3 to be 4 - 2 sqrt(2) ~= 1.172. The
eigenvalues of tridiag(c, a, c) are a + 2c cos(k pi / (n+1)), so the
true value is 4 - sqrt(2) ~= 2.586. The test had been quarantined for
failing to match an expectation that was never right.
rtx-fsi is untouched and stays 26/26.
Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>
