FitModelScale fits ~113 (k_sol, b_sol) grid points, each a full
Levenberg-Marquardt over every working reflection, and it is the largest single
cost of --model (every fit_model call: the first fit, the twin-law probe, the
fit after the rigid body, each null replicate). It ran on one thread.
Each point starts from fit_isotropic_b_approximately(), which sets k_overall
and b_star from the data and the point's solvent pair alone, so no point
depends on the one before it. The points of each pass (coarse, then the
refinement around the coarse winner) now run in contiguous chunks, each on its
own copy of the Scaling, and the winner is read off afterwards in grid order
with the serial rule (lowest finite R, first on a tie). Each point's arithmetic
is unchanged, so the result is the serial loop's bit for bit. Where
fit_isotropic_b_approximately() has five or fewer reflections to fit on it
returns without setting anything and points would chain, so there the grid is
still walked serially on the caller's Scaling.
Inside a null replicate (a pool worker) the chunks run inline, as before.
To check: MODEL_* keys and md5 of the maps/.mtz/_model.cif identical with and
without this commit on the audit set; model-phase time on a fit-dominated set.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013nW6FNRP1bBJJ8pfHiByAT
leonarski_fandClaude Opus 5
2f727b1975