oh, right, what I suggested isn't what you asked for, sorry.
On Mon, 19 Jun 2023, 13:56 John Cremona, <john.crem...@gmail.com> wrote: > Thanks Dima for the suggestion. I'm not sure that this does what I need: > the associated directed graph has each edge directed, which is not what I > was needing, and the faces of the directed graph look identical to those of > the original -- in particular, the edges of each face are tuples (x,y) > where both (x,y) and (y,x) appear on different faces (as I need to always > hold) regardless of the orientation of the edges. > > I will keep on experimenting. My polyhedra are small and few enough that > check the orientations of each is not very time-consuming. > > John > > On Monday, June 19, 2023 at 12:08:18 PM UTC+1 Dima Pasechnik wrote: > >> On Mon, Jun 19, 2023 at 11:18 AM John Cremona <john.c...@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...@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/08ace3c1-1e96-427a-97a1-53605ca42742n%40googlegroups.com > <https://groups.google.com/d/msgid/sage-support/08ace3c1-1e96-427a-97a1-53605ca42742n%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- 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/CAAWYfq0M-cXk1qM-c3GDm4bzUSfdegH7UQ-rfjHbZWQ8tpW2Bg%40mail.gmail.com.
