I'm not sure what MG is doing with an "unstructured" problem. I assume you are not using DMDA. -pc_type gamg should work I would configure with hypre and try that also: -pc_type hypre
As Matt said MG should be faster. How many iterations was it taking? Try a 100^3 and check that the iteration count does not change much, if at all. Mark On Mon, Jun 26, 2023 at 11:35 AM Vanella, Marcos (Fed) via petsc-users < petsc-users@mcs.anl.gov> wrote: > Hi, I was wondering if anyone has experience on what combinations are more > efficient to solve a Poisson problem derived from a 7 point stencil on a > single mesh (serial). > I've been doing some tests of multigrid and cholesky on a 50^3 mesh. *-pc_type > mg* takes about 75% more time than *-pc_type cholesky > -pc_factor_mat_solver_type cholmod* for the case I'm testing. > I'm new to PETSc so any suggestions are most welcome and appreciated, > Marcos >
