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Add a multi-level Schwarz preconditioner
This PR adds a multi-level Schwarz preconditioner to Ginkgo. The main objective is to be able to use this as preconditioners for Krylov solvers, but combined with IR, it can be used as a solver as well.
TODO:
- [x] Store coarse solvers as Multigrid levels (RAP) ~~+ [ ] Incorporate Overlap.~~
Currently, this is a single GPU version, but the core class and implementation should carry over to the distributed setup.
Is the implementation intended for single-executor or distributed use? The interface seems to imply the former
Note: This PR changes the Ginkgo ABI:
Functions changes summary: 0 Removed, 270 Changed (7047 filtered out), 1283 Added functions
Variables changes summary: 0 Removed, 0 Changed, 0 Added variable
For details check the full ABI diff under Artifacts here
@upsj What do you think of two separate classes, one for distributed and one for single GPU , differing in namespaces gko::preconditioner::Schwarz and gko::distributed::preconditioner:Schwarz.
@pratikvn sorry for leaving this hanging. Yes, that's what I had in mind. It might be that there is some overlap (haha 😁) in the kernels that can be used to set up overlap information, but the interfaces are probably too different to be useful. Still, I think the interfaces should both be designed with overlap in mind, do you have a prototype with overlap capabilities somewhere that we can use as guidance?
Closing as the same interface for distributed and non-distributed is not reasonable.
@upsj, I had a preliminary overlap interface somewhere, I will have to dig that up. But it was still only contiguous overlaps (ranges) and not disjoint. To be more generic, It would be better to have an interface that supports disjoint overlaps, which I still need to think about a bit.