Update products with the block-Jacobi preconditioner

[amontoison]

No description provided.

[amontoison]

For Block-Krylov methods we need operator-matrix products.
I added a method for CPU matrices.

I don't understand why you implemented a kernel for the CUDA version.
Is it not possible to perform a asynchronous gemm with each block and synchronize at the end?

A block-Jacobi should not have overlap.

ps: I also added some view for the CPU variants to avoid unnecessary copies.

[frapac]

The preconditioner on master is deprecated. Please have a look at the fp/precond_experiments branch.

I don't understand why you implemented a kernel for the CUDA version.

https://github.com/exanauts/ExaPF.jl/blob/fp/precond_experiments/src/LinearSolvers/preconditioners.jl#L182-L188

A block-Jacobi should not have overlap.

The block-Jacobi preconditioner was just an intermediate step to implement a overlapping Schwarz preconditioner. Hence the overlap found in the code. Feel free to rename the preconditioner if you prefer.

ps: I also added some view for the CPU variants to avoid unnecessary copies.

The CPU implementation is here just for debugging purpose, but feel free to clean it.

My opinion is that preconditioners do not belong to ExaPF and should be moved in a new package.

[codecov-commenter]

Codecov Report

Merging #278 (368237b) into main (dbc883e) will increase coverage by 0.04%.
The diff coverage is 70.00%.

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@@            Coverage Diff             @@
##             main     #278      +/-   ##
==========================================
+ Coverage   74.50%   74.55%   +0.04%     
==========================================
  Files          31       30       -1     
  Lines        4182     4201      +19     
==========================================
+ Hits         3116     3132      +16     
- Misses       1066     1069       +3     

Files	Coverage Δ
src/LinearSolvers/preconditioners.jl	81.93% <70.00%> (+0.65%)	⬆️

... and 5 files with indirect coverage changes

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