The projected histogram is sampled every 1/(2*max_length) of 1/d, so a row
of length L between max_length and 2*max_length folds to 2*max_length - L and
peaks there as sharply as a real row. At the default 500 A bound a 602 A axis
came back as ~400 A and a 701 A axis as ~299 A; the folded cell still indexed
59/60 and 37/60 validation frames (only the reflections whose index lands on
an integer of the folded period), so the long-axis rescue, gated on a poor
pass, never ran. The same fold also turned real >500 A lattice combinations
of shorter-axis cells into spurious shortlist rows.
Each shortlisted row is now asked once, by a direct Fourier sum over the spot
positions (no sampling, so no fold), whether the spots carry its own length or
its partner 2*max_length - L more strongly, and keeps the stronger. Partners
within 0.1 of an integer multiple are left alone (a harmonic, settled
elsewhere). Refinement accepts rows up to 2*max_length when one was unfolded.
Measured: a hexagonal P6122 c=602 A EIGER set and a P6522 c=701 A CCD set,
both indexed de novo on the folded cell before, now index the deposited cell
60/60 and merge to R-free 0.31 / 0.22 against the models (the same numbers as
-C with the deposited cell). Of 13 long-axis battery sets, 7 are bit-identical
(p.hkl md5) and 2 never unfold a row, 8v4o and 9yl4 have the same intensities (CC 1.0) without needing
the long-axis rescue, 4mtk refines a cell closer to the deposit at half the
wall time, 4nwv merges better (R_meas 0.58 -> 0.47, ISa 6.7 -> 8.4).
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SVmAWnzCmRKAXVUCdc4iNi
leonarski_fandClaude Opus 5.5
acd4a50b74