[petsc-users] API cal to set mg_levels_pc_type

[Jed Brown]

Barry Smith <bsmith at petsc.dev> writes:

>> 1. Is there a way to set the mg_levels_pc_type via an API call?
>> 2. Are there any changes in efficiency expected with this new PC?
>
>   This was changed mainly because PCSOR is not effective (currently in PETSc) for GPUs. For CPUs
> it will definitely be problem dependent, you need to try both smoothers at scale to determine the most effective.

When running on CPU for elliptic problems, -mg_levels_ksp_type richardson -mg_levels_ksp_max_it 1 -mg_levels_pc_type sor is often a good choice.

The new default (Chebyshev/Jacobi) is efficient on both CPU and GPU. The setup cost for this configuration is lower in 3.17 because the GAMG setup needs the same eigenvalue estimates.