Supporting pytorch_sparse

[mpariente]

Hi again,

You might be aware of this project (pytorch_sparse) which is really cool.
It's be great to support their SparseTensor as an input to solve, or maybe adding another method for those tensors.

I don't know much about sparse format but it does support efficient csc conversion (here), it might be worth having a look.

[flaport]

I have come across the pytorch_sparse library indeed. However, I have never used it. If it is indeed the de-facto sparse library for PyTorch, it might indeed be a good idea to also work with their sparse tensor implementations.

I'll have a look at their repo to get more acquainted.