A new correction surface, fitted after the time x detector surface and
before the goniometer-frame 8x8 grid: log A is a sum of real spherical
harmonics (l = 1..6, 48 terms) of the diffracted-beam direction de-rotated
into the crystal frame. The incident-beam path depends on phi alone and is
in the per-frame scale already.
It runs through ApplyCellSurface unchanged in everything but the update:
the cells are 32 x 64 equal-solid-angle direction bins, and each round the
per-cell sums (ref2, cross, the same damping) become one ridge-regularised
Gauss-Newton step on the coefficients (prior width 0.1/l per degree-l
coefficient) instead of independent per-cell steps. The half-set Fisher-z
gate adopts or refuses it exactly as it does the grids; where it is
refused, the grid after it sees what it saw before.
Why: the folded 8x8 grid (hemispheres share a cell) is the weak basis for
long-wavelength absorption. Offline, held out by unique reflection, this
basis lowered held-out scatter 4-8% on 6 of 11 long-wavelength sets where
no cell grid did, raised model-phased anomalous peaks 0.02-0.2 sigma, and
was neutral on hard-X-ray controls.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01D1G8gJVAy6gp1K5Dz3NE5C
