forum.polymake.org

I've noticed that the commands hypersimplex(2,3) and hypersimplex(3,4) produce strange results. I expect hypersimplex(n-1,n) to give (n-1)-simplices, but get the following:

I get similar (obviously incorrect) results for hypersimplex(1,3) and hypersimplex(1,4).

Can someone take a look at this? (I am using polymake version 3.0.)

Thanks!

Thanks for pointing this out. Indeed, this is a bug.

The reason is that (for convenience and speed) the client writes VERTICES and FACETS, but they do not fit if the hypersimplex degenerates to a simplex. In fact, a worse version of the same problem occurs for k=0 or k=d.

The issue is resolved in polymake's git repository, and so it will be correct in the next release. We can provide a patch for 3.0 if necessary.
The solution is (1) to not write FACETS and VERTICES_IN_FACETS in the simplex case, (2) to forbid parameters which lead to the degeneration to a point.

Okay, thanks! I won't need a patch for this -- I was just using these for some testing.