[petsc-dev] Right-preconditioned GMRES

[Mark Adams]

Try -pc_asm_overlap 0 with ASM.

And I trust the KO run works with 1 processor (direct solve)

On Sun, Oct 13, 2019 at 3:41 AM Pierre Jolivet via petsc-dev <
petsc-dev at mcs.anl.gov> wrote:

> Hello,
> I’m struggling to understand the following weirdness with PCASM with exact
> subdomain solvers.
> I’m dealing with a very simple Poisson problem with Dirichlet + Neumann
> BCs.
> If I use PCBJACOBI + KSPPREONLY or 1 iteration of GMRES either
> preconditioned on the right or on the left, I get the expected result, cf.
> attached screenshot.
> If I use PCASM + KSPPREONLY or 1 iteration of GMRES preconditioned on the
> left, I get the expected result as well.
> However, with PCASM + 1 iteration of GMRES preconditioned on the right, I
> don’t get what I should (I believe).
> Furthermore, this problem is specific to -pc_asm_type restrict,none (I get
> the expected result with basic,interpolate).
>
> Any hint?
>
> Thanks,
> Pierre
>
> $ -sub_pc_type lu -ksp_max_it 1 -ksp_type gmres -pc_type bjacobi
> -ksp_pc_side right -> bjacobi_OK
> $ -sub_pc_type lu -ksp_max_it 1 -ksp_type gmres -pc_type asm -ksp_pc_side
> left -> asm_OK
> $ -sub_pc_type lu -ksp_max_it 1 -ksp_type gmres -pc_type asm -ksp_pc_side
> right -> asm_KO
>
>
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