gh-36849: Problem with orientations of simplices in simplicial complex maps.
Problem with orientation of simplices in simplicial complex maps
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In rare cases, Sage incorrectly computes the chain complex map
associated to a map of simplicial complexes. The problem is that the
orientation of each simplex in the image is not correctly compared to
its actual orientation in the codomain: an edge `(f(v), f(w))` is not
compared correctly to see whether the actual simplex in the codomain is
stored as `(f(v), f(w))` or `(f(w), f(v))`.
I think that the default sorting of vertices (and hence simplices) means
that this usually doesn't come up, but it can arise when the vertices do
not have an obvious ordering. See
https://ask.sagemath.org/question/74754/chain-morphism-between-
subdivisions/ for one such case.
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URL: https://github.com/sagemath/sage/pull/36849
Reported by: John H. Palmieri
Reviewer(s): Travis Scrimshaw
