I'm not sure I understand what you think is wrong; the output you are describing looks ok to me. The polyhedron is a square, 2- dimensional. It has four 1-dimensional faces, and .facial_incidences() is listing the indices of those faces followed by the indices of the vertices contained in each face.
Are you writing triangularization code for arbitrary dimensions or just for 3d? I realized that although I was mainly using it for rendering, other people are interested in triangularizations for other reasons and in other dimensions. Cheers, Marshall On Sep 20, 3:08 pm, "Arnaud Bergeron" <[EMAIL PROTECTED]> wrote: > About this, I have encountered behaviour which I find strange (and > also breaks the current code), but it may just be because I am not > familiar enough with polytopes > > sage: p2 = Polyhedron([[0,0,0], [0,0,10], [10,0,10], [10,0,0]]) > > This should just be a square on the y plane right? > > sage: p2.facial_incidences() > [[0, [0, 3]], [1, [0, 1]], [2, [1, 2]], [3, [2, 3]]] > > But this says to me it's actually four segments with the center empty. > > So I have two questions: > > 1. Is the polyheron above actually a square? > 2. Is the facial incidence list describing a square or four edges > along the side of one? > > If 1 is yes, I think I found a bug. > > If 2 is yes, my new code works! > > Arnaud > > > > > Cheers, > > Marshall Hampton > > > On Sep 20, 11:35 am, "Arnaud Bergeron" <[EMAIL PROTECTED]> wrote: > >> 2008/9/20 mhampton <[EMAIL PROTECTED]>: > > >> > Hi everybody, > > >> > This is mainly about making the lrs optional package standard to > >> > improve some polytope-related calculations. > > >> > My original motivation for lrs (linear reverse search) is that is a > >> > very different algorithm/implementation for computing exact convex > >> > hulls in arbitrary dimensions. Currently the default for this in Sage > >> > is cddlib, which uses the "double description" method. There are > >> > classes of polytopes for which lrs is much faster than cddlib, > >> > although in my experience cddlib does better most of the time. lrs is > >> > also nice in that it doesn't use much memory. Polymake also uses > >> > these two methods, plus a third, the "beneath and beyond" method. I > >> > still need to modify the Polyhedron class to make use of lrs if it is > >> > present. > > >> > I am now thinking more about nice renderings of polytopes, and for > >> > that I need better triangulation code. I have a really bad algorithm > >> > in polyhedra.py right now that needs to be improved or replaced. I > >> > see at least three options for this: > > >> > 1) I could just improve the code I already have. I've actually > >> > already done this, and I guess I will submit a ticket soon. But I am > >> > not an expert in this area and I don't think even my improved versions > >> > would be good enough for serious users. > > >> > 2) The option I like best in the short term is to make lrs standard > >> > and use it for computing triangulations. The lrs algorithm computes a > >> > triangulation anyway, and its probably one of the faster methods > >> > available for doing so. lrs is small (spkg is 120kb) and compiles > >> > quickly. Its mature code, its been maintained and improved for about > >> > 10 years. > > >> > 3) Eventually it would be good to add TOPCOM. Apparently it is what > >> > people use who do research that involves triangulations. But this is > >> > a bigger task than I can take on right now. Its a much larger piece > >> > of code than lrs, but it would add more functionality. > > >> > So I can do option (1) very soon, and option (2) in the next month or > >> > so unless people have objections. > > >> I am beginning to work on the triangularization code just now, since > >> it was on the list of requested items when I asked for thing to do in > >> graphics. It should be ready in about a week if all goes well. > > >> Arnaud > > >> > To help, install the optional package and test it by downloading: > >> >http://www.d.umn.edu/~mhampton/lrs_test.ext > >> > and run $SAGE_ROOT/local/bin/lrs your_path_to_lrs_test/lrs_test.ext > >> > where of course you replace "your_path_to_lrs_test" with the path to > >> > the file. I've done this on a couple of intel macs (10.4 and 10.5), I > >> > don't expect any problems on linux and I have no idea about Solaris. > > >> > Cheers, > >> > Marshall Hampton > > >> -- > >> La brigade SnW veut vous recruter -http://brigade.snw.googlepages.com > > -- > La brigade SnW veut vous recruter -http://brigade.snw.googlepages.com --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to [email protected] To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sage-devel URLs: http://www.sagemath.org -~----------~----~----~----~------~----~------~--~---
