See the very end of the section https://petsc.org/release/manual/ksp/#multigrid-preconditioners on how to control the smoothers (and coarse grid solve) for multigrid in PETSc including for algebraic multigrid.
So, for example, -mg_levels_pc_type fieldsplit would be the starting point. Depending on the block size of the matrices it may automatically do simple splits, you can control the details of the fieldsplit preconditioner with -mg_levels_pc_fieldsplit_... and the details for each split with -mg_levels_fieldsplit_.... See src/ksp/ksp/tutorials/ex42.c for example, usage Feel free to ask more specific questions once you get started. > On Jul 26, 2023, at 9:47 PM, Michael Wick <[email protected]> wrote: > > Hello PETSc team: > > I wonder if the current PETSc implementation supports using AMG > monolithically for a multi-field problem and using fieldsplit in the smoother. > > Thank you very much, > > Mike
