On Mon, Jun 19, 2023 at 11:18 AM John Cremona <john.crem...@gmail.com> wrote: > > I have some quite small graphs which are polyhedral, each is the 1-skeleton > of a (connected convex) polyhedron such as a cube, tetrahedron, etc, > constructed from a list of edge pairs. > > I can get the faces of one of these, say G, via G.faces(). This returns a > list of lists of vertices, each one being a list of the vertices of one face > in some cyclic order. So each face in the list has an implied orientation. > OK so far. > > What I want is for the orientations of the different faces to be coherent, > coming from a single orientation of the surface. Expliticly that means that > each edge xy, which will appear in exactly two faces, appears once in each > direction, i.e. x before y (cyclically) in one and the other way round in the > other. > > It is possible that G.faces() is already returning such a globally oriented > list of faces, as experimentation suggests, but I need to be certain -- > otherwise I can write code to check and if necessary reverse some faces. I > would prefer not to have to though. > > The docstrong of G.faces() does not make this clear (at least not to me).
You can call G.strong_orientation() to get an orientation of the edge of your graph, and use it. HTH Dima > > -- > You received this message because you are subscribed to the Google Groups > "sage-support" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to sage-support+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/sage-support/CAD0p0K5e9ch3tgrM2RAHxQieVOqG%2BEX37fyWj7BwF0ns-NTPpA%40mail.gmail.com. -- You received this message because you are subscribed to the Google Groups "sage-support" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-support+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/sage-support/CAAWYfq1CD25svmrm-VxCXHS02oGrzPE5V%2BZPfxAdX1qwN2uMFA%40mail.gmail.com.
