Sparse matrix format interfaces about sparsearrays.jl

[ViralBShah]

The problem right now is that SparseArrays.jl is a Julia stdlib, and I believe it can't be removed. Something to do with type piracy of * and . @KristofferC tried to excise it and realized we couldn't.

I would personally prefer to get it excised and also LinearAlgebra, and I also like the idea of the Interfaces package. In the meanwhile we can certainly add the types and machinery you suggest so that they can be extended by downstream packages.

Would be good to have @SobhanMP and @rayegun chime in as well, before any PRs are put together.

[SobhanMP]

The interface is generic; I only added CSC and dense matrix support because that's what's implemented in this package. Nothing is really stopping you from adding CSR support, and it should be composable with other types. https://sobhanmp.github.io/SparseExtra.jl/iternz/

[j-fu]

Just FYI: there is also https://github.com/gridap/SparseMatricesCSR.jl

[termi-official]

Thanks Jürgen. Let me then also mention for completeness of the thread the packages
https://github.com/BacAmorim/ThreadedSparseCSR.jl/
https://github.com/youwuyou/Ginkgo.jl
https://github.com/fredrikekre/HYPRE.jl
providing CSR formats

[termi-official]

Thanks for the additional context @ViralBShah . I went ahead and drafted what I have in mind and could need some feedback. The alternative would be to move the CSR code into a different package for now (SparseMatricesCSR.jl, if it is still maintained?) and strip the open PR down to the changes which are necessary to enable the AbstractSparseMatrixCSR interface.

Edit: If there is a third option I am still happy to hear. (And no worries, I have not forgot about the sparse matrix iterator interface tho Raye)

[SobhanMP]

forgot about the sparse matrix iterator interface tho Raye

Is this something different than #167?

[termi-official]

From what I understood Raye's idea was to have a generic interface which works across different formats. The PR looks like it is tailored to provide iterators primarily with CSC in mind

@inline getcolptr(x::SparseIndexIterate) = getcolptr(x.m)
@inline getrowval(x::SparseIndexIterate) = getrowval(x.m)
@inline getnzval(x::SparseIndexIterate) = getnzval(x.m)

right?