Hello Dominique, One thing to note here is that the graph you are trying to plot is not a planar triangulation.
The planar drawings output by sage are precisely those proposed by Schnyder for planar triangulations. What happens when you ask for a planar drawing of a planar non triangulated graph? 1. Augment the input graph to a triangulation by adding edges (if needed). 2. Obtain the coordinates for the planar drawing of the augmented graph. 3. Use those positions for the input graph (deleting edges will preserve planarity of the drawing). You are right in that the drawings output by sage do not correspond to the planar embedding. The get_embedding method says vertices are ordered in clockwise order whereas the drawing output by sage displays them in counter-clockwise order. There is an interesting aspect of Schnyder drawings though. They have been generalized to planar 3-connected graphs and that yields drawings still in an O(n)xO(n) grid where each of the faces is convex (this might be something interesting to implement ;-). Unfortunately the graph you are trying to draw is not even 3-connected. The "problem" with this is that the embedding may not be unique. Hope this helped clarifying further some of your questions. Best, Fidel On Sunday, October 18, 2015 at 12:56:14 PM UTC-4, Dominique Laurain wrote: > > > Sorry, maybe "clockwise" doesn't mean anything with two neighbours > > Mea culpa > > Dominique. > > -- 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 [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/sage-support. For more options, visit https://groups.google.com/d/optout.
