[petsc-dev] Right-preconditioned GMRES

[Pierre Jolivet]

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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