On Sep 20, 9:05 am, mhampton <[EMAIL PROTECTED]> wrote:
> Hi everybody,
Hi Marshall,
> 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.
You need to propose lrs for inclusion, but note that it needs to
fulfill the inclusion procedure. I see it rather unlikely for TOPCOM
to become standard in Sage since it builds for a long time and is
rather large (we talked about this for a while a couple months bag).
> 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
Cheers,
Michael
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