Hellooooooooooooo ! > for a simple graph, trace_faces() gives the expected answer for the faces > of a planar graph
That's a good news :-D the face that should exist between just nodes 3,4 and 5 is not found, it's > replaced with a face around nodes 1,2,3,4,5. Any ideas what is wrong, or > other ways of getting an accurate list of the faces in a planar graph? > What makes you think that the faces returned by Sage are wrong ? A planar graph can have different planar embeddings, and so different sets of faces. If you call .show() with a specific position for the vertices, this may result in a planar graph and you may see some faces defined, but there is no reason why .trace_faces() should return the faces using the positions you defined earlier for the plot ! In the documentation, .trace_faces() tells you that it can either find the embedding by itself, or use an "embedding" argument. In you case you did not define the embedding, so trace_faces() finds its own. As, just before, you called .is_planar(set_embedding=True), the embedding used by traces_faces() is the one that has been found by is_planar. But as you did not give to is_planar() the position of your vertices (and it does not accept positions of vertices as an input anyway),then is computes its own embedding. That's all. So unless you think that the faces returned by Sage do not correspond to a planar embedding, technically Sage makes no error. Now, if you want Sage to work with the position of the vertices you used for the plot, what you should do is write a short function which transforms (x,y) positions for the vertices into a combinatorial embedding. Then, you will be able to call .set_embedding() with that embedding, and then trace_faces() will give you the result that you expect, i.e. the faces defined by your embedding. And if you do that, please contribute to Sage by submitting your code, as I guess this would definitely be useful to others :-) Good luuuuuuuuuuuuuuuuuuuuuuuuuuuck ! Nathann > > > I'm using 'Sage Version 5.13, Release Date: 2013-12-15' > > I realize that trace_faces has been deprecated to just faces() per this > discussion: http://trac.sagemath.org/ticket/15551 > > but when I run > S.faces() > > I get the error > AttributeError: 'Graph' object has no attribute 'faces' > > -- 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 post to this group, send email to sage-support@googlegroups.com. Visit this group at http://groups.google.com/group/sage-support. For more options, visit https://groups.google.com/d/optout.
