[petsc-dev] ASM for each field solve on GPUs

Jed Brown jed at jedbrown.org
Wed Dec 30 17:46:55 CST 2020

Mark Adams <mfadams at lbl.gov> writes:

> I see that ASM has a DM and can get subdomains from it. I have a DMForest
> and I would like an ASM that has a subdomain for each field. How might I go
> about doing this? (the fields are not coupled in the matrix so this would
> give a block diagonal matrix, and thus exact with LU sub solvers.

The fields are already not coupled or you want to filter the matrix and give back a single matrix with coupling removed?

You can use Fieldsplit to get the math of field-based block Jacobi (or ASM, but overlap with fields tends to be expensive). Neither FieldSplit or ASM can run the (additive) solves concurrently (and most libraries would need something to drive the threads).

> I am then going to want to get these separate solves to be run in parallel
> on a GPU (I'm talking with Sherry about getting SuperLU working on these
> small problems). In looking at PCApply_ASM it looks like this will take
> some thought. KSPSolve would need to be non-blocking, etc., or a new apply
> op might be needed.
> Thanks,
> Mark

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