Every candidate the indexer forms is Niggli-reduced and primitive; the reference cell was
compared against them exactly as typed. For a centred lattice those are different numbers
entirely - a conventional F-cubic cell reduces to a rhombohedron with 60-degree angles, a
centred monoclinic cell to axes it shares none of - so the true candidate failed the 5% test and
the run reported that it had found no lattice. A user who supplied the cell as it is published
was worse off than one who supplied nothing.
The reference is now expanded into the primitive lattices its six numbers could stand for, one
per centring, each reduced the way a candidate is; a candidate matching any of them is kept. The
cell as typed stays in the set, so the indexer that returns the basis it was handed is
unaffected.
The cost is real and stated: a wrong cell now gets several chances to match rather than one. The
controls that hold are on data - deliberately wrong cells are still refused, and every cell that
worked before gives the same answer to the digit - but a synthetic lattice can be made to match
through a centring hypothesis it has no right to, and no volume test tightens that without
excluding a true candidate this corpus already contains.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EFEJG6WBQv8th4UJFNe53N
leonarski_fandClaude Opus 5
485bbeaf71