[petsc-users] Questions about multigrid preconditioner and multigrid level

[Young Hyun Jo]

Hello, I'm Young Hyun Jo, and I study plasma physics and particle-in-cell
simulation.
Currently, I'm using PETSc to solve a 3D Poisson's equation in the FDM
scheme.
I have one question about the multigrid preconditioner.
When I use PCG(KSPCG) with the multigrid preconditioner(PCMG), I get an
error if I don't use the appropriate multigrid level for the grid number.
For example, If I use 129 grids, I can use 7 multigrid levels.
However, If I use 130 grids, I can't use any multigrid levels but one.
So, It seems that the grid number is better to be (2*n + 1) to use
multigrid preconditioner.
Is this correct that the multigrid conditioner has some restrictions for
the grid number to use?
It will be really helpful for me to use PETSc properly.
Thanks in advance.

Sincerely,
Young Hyun Jo
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