SearchSpaceGroup: drop the log10(chi2_ref) widening of the point-group
chi^2-ratio bound and tighten max_merge_chi2_ratio 2.0 -> 1.85. The
variance-floor fix removed the error-model miscalibration the widening
compensated for, so the widening now only let a partial merohedral twin
through (Ins_H_2 R3->R32 twin 2-fold: ratio 2.01). Every genuine high
symmetry across the rotation-test battery stays within ~1.7x (worst real
case Thau P41212 at 1.71), so 1.85 keeps R3 in its true lower symmetry.
TwinningAnalysis: make the <I^2>/<I>^2 second moment robust - skip
noise-only shells (<I/sigma> < 1) and reject Wilson outliers (E^2 > 8)
with one shell-mean re-iteration, so a single strong reflection in a
collapsed-mean shell no longer dominates the moment. Add
MerohedralTwinningPossible: in a holohedral Laue class (4/mmm, 6/mmm,
m-3m, rhombohedral -3m) no twin law exists, so a low <|L|> there is a
statistical artefact and is no longer flagged as twinning.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
leonarski_fandClaude Opus 4.8
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