Hello everyone!I would like to compute the cup-product of two chains in the cohomology of a simplicial complex.
What I have so far, is that I have the simplicial complex realized as a SimplicialComplex in sage and I can compute its cohomology groups. They are: {0: 0, 1: Z x Z, 2: Z^28, 3: Z^9}. What I would like to do, is to take two generators of the cohomology group in degree 1 and compute that their cup-product is non-trivial. What is the best way to do this?
As I gather from Trac issue #6102, I can't simply compute the cohomology ring, as this functionality is not yet implemented. So I have to do this by hand, but that's okay. AFAICT, there are two things I need to figure out.1) How can I get my hands on two representatives of the generators of the first cohomology group? I am not sure, whether I can have sage compute these for me (see ticket #6100). If yes, how? If no, I could maybe construct these two by hand (as I "know" how my simplicial complex "looks"). But in what format do I have to construct these chains so that I can use them in step 2?
2) How can I compute coboundaries of chains in the cochain complex? I know that sage will give me the cochain complex induced by my simplicial complex including the (co)boundary maps. But how do I apply these coboundary maps to chains? What format do these chains need to have?
dimension 1 boundary a1 = - 1 * a3 - 1 * a10 boundary a2 = - 1 * a2 - 1 * a5 boundary a3 = + 1 * a4 + 1 * a9 boundary a4 = + 1 * a6 + 1 * a12 boundary a5 = + 1 * a2 + 1 * a11 boundary a6 = - 1 * a4 - 1 * a11 boundary a7 = + 1 * a4 + 1 * a8 boundary a8 = + 1 * a5 + 1 * a14 boundary a9 = - 1 * a9 + 1 * a10 boundary a10 = + 1 * a1 + 1 * a6 boundary a11 = - 1 * a6 - 1 * a8 boundary a12 = + 1 * a5 + 1 * a7 boundary a13 = + 1 * a8 + 1 * a14 boundary a14 = + 1 * a7 + 1 * a9 ...
But I don't see any information what face, say, a1 corresponds to. Am I missing something?
Here is a first implementation of the cup product.
If there is interest, I would be willing to put in the additional work to add this function to Sage. But for that I would need to learn about the all the other issues that I don't know anything about but that I should take care of first :)
And don't forget that if you can stay for a few days after, there is
Sage Days 35.5:
http://wiki.sagemath.org/days35.5
Thanks,
Jason