2008/9/20 mhampton <[EMAIL PROTECTED]>: > > OK, well I have plenty of projects so I won't work too hard on that > right now and see what you come up with. I need something that works > for a talk I am giving in about a month, but if necessary I can use > the "bandaid" code I already have, which works about 98% of the time > for the stuff I care about, and I know how to make it a little > better. I am happy to review code in this area or discuss it further.
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 sage-devel@googlegroups.com 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 -~----------~----~----~----~------~----~------~--~---
