[petsc-users] Multigrid with PML

[Safin, Artur]

Dear PETSc community,

I am working on solving a Helmholtz problem with PML. The issue is that I am finding it very hard to deal with the resulting matrix system; I can get the correct solution for coarse meshes, but it takes roughly 2-4 times as long to converge for each successively refined mesh. I've noticed that without PML, I do not have problems with convergence speed.

I am using the GMRES solver with GAMG as the preconditioner (with block-Jacobi preconditioner for the multigrid solves). I have also tried to assemble a separate preconditioning matrix with the complex shift 1+0.5i, that does not seem to improve the results. Currently I am running with

   -ksp_type fgmres \
   -pc_type gamg \
   -mg_levels_pc_type bjacobi \
   -pc_mg_type full \
   -ksp_gmres_restart 150 \

Can anyone suggest some way of speeding up the convergence? Any help would be appreciated. I am attaching the output from kspview.

Best,

Artur

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