In the default rotation (rot3d) path only G is refined - B is fixed, mosaicity
is pinned and the wedge is not refined - so the predicted intensity G*coeff is
linear in G and the robust (Cauchy) per-image scale is a 1-D M-estimate. Solve
it directly by iteratively reweighted least squares (a few closed-form weighted
ratios) instead of building a Ceres problem per image. Ceres is kept for the
cases that are genuinely nonlinear: refining the B-factor or the rotation wedge.
Same Cauchy objective as the Ceres path, but ~4x faster at scaling and ~30%
faster overall on the /data/rotation_test battery, with space group, cell, ISa,
completeness and CC1/2 matching across all 18 crystals (the two that look
different, EP_cs_01-17 and EcwtAL500, are run-to-run unstable for both solvers).
lyso_ref scaling 25.2->4.3s, cytC_2 15.2->2.6s, battery total 468->316s.
Also drop the per-image G/B regularizers (gated by GetScalingRegularize, which
nothing enables) and the now-unused RegularizationResidual.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
leonarski_fandClaude Fable 5
1ca5a69054