Hi everyone, Currently, I am working on the ticket:
http://trac.sagemath.org/ticket/18442 which implements a barycentric subdivision of a polytope. For this I use the containment check. In the tests, it works fine for a regular pentagon over AA but not over RDF. The problem can be seen with the following code: sage: P = polytopes.regular_polygon(5) sage: a_vertex = P.vertices()[0] sage: for facet in P.Hrepresentation(): print facet.contains(a_vertex), facet.interior_contains(a_vertex) True False True True True False True True True True sage: P = polytopes.regular_polygon(5, base_ring=RDF) sage: a_vertex = P.vertices()[0] sage: for facet in P.Hrepresentation(): print facet.contains(a_vertex), facet.interior_contains(a_vertex) True True True True True True True True True True (The first output is as expected: the vertex is not contained in the interior of exactly 2 facets. This is not the case in RDF) Right now, I have the following question in mind: Does it make sense to have polyhedron over RDF? By which I mean: it can not even deal with containment of faces properly. Reasonably, the user knows that and will use a different ring... But what if? I know that it is practical to have polyhedron defined over RDF for different reasons, but there is a fundamental change in the results (and pretty much any method doing computations) if the ring changes. I'm NOT asking to remove RDF as a possible ring. The reason I'm asking is that I have to use such containment check to implement the method barycentric subdivision for polyhedron, but then it breaks for polyhedron defined on RDF because of that. So there are methods that simply do not work when the ring is RDF. Maybe this analogy could explain my thoughts: If we compute the eigenvalues of a matrix defined over RDF, sage warns us that the results may go bad. It doesn't if the matrix is rational... Could such a warning be issued when working with RDF? And then put NotImplemented whenever it is known that RDF could cause trouble (and then fix it for that specific ring?). I could simply set the barycentric subdivision for polyhedron over RDF not to be implemented, but I feel this would not answer the problem raised anyway. Thanks! -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+unsubscr...@googlegroups.com. To post to this group, send email to sage-devel@googlegroups.com. Visit this group at http://groups.google.com/group/sage-devel. For more options, visit https://groups.google.com/d/optout.
