Matrix free petsc solver with multigrid (MG or GAMG) preconditioner

Linear Algebra
1

Hi.
I want to use petsc MG or GAMG preconditioner in conjunction with matrix free approach given here.
So in line 346, I want
solver.getPC().setType(PETSc.PC.Type.GAMG)
instead of
solver.getPC().setType(PETSc.PC.Type.NONE)
Is it possible to use petsc preconditioners directly or do I need to define my own preconditioner? I am presuming something like PCSHELL

2

Hi,

you will need to build a matrix-free preconditioner within PCSHELL, PETSc built-in preconditioners need access to the matrix entries. Algebraic MG, in particular, needs the assembled matrix, but you can construct your own geometric MG matrix-free. You can also build simpler matrix-free preconditioners (e.g. SOR) or physics-based ones using PCSHELL, depending on the problem you are trying to solve.

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