On Wednesday, 1 July 2015 14:59:20 UTC+1, Volker Braun wrote: > > cdd does not correctly handle floating point precision issues. It works > for non-degenerate input, for everything else there are no guarantees. > > > > On Wednesday, July 1, 2015 at 12:27:09 PM UTC+2, Dima Pasechnik wrote: >> >> While working on http://trac.sagemath.org/ticket/10276, we had trouble >> running Polyhedron with RDF precision. >> An explicit example showing the issue is in >> http://trac.sagemath.org/raw-attachment/ticket/10276/x.sage >> >> What happens is that Polyhedron() finishes normally, but it creates >> something that looks like inconsistent data >> (a closer inspection reveals that one of the 136 facets of this polytope >> does not "contain any vertices", in the >> sense that the corresponding inequality is not satisfied with equality >> (within the meaningful precision)). >> At least this data is not good enough to compute the face lattice of it. >> >> Without a better knowledge of Polyhedron() code it is hard for me to >> decide whether this is a bug. >> >> Any comments? >> Thanks, >> Dima >> >> PS. if I use non-default 'field' backend I also get some weird error on >> this data, but it works fine if I use >> QQ as the base_ring. >> > one way or another if the backend is 'field' then base_ring.is_exact() should be True, as _is_zero() is exact in this case. Currently this is not checked, and is a bug, IMHO.
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