John, For any non-trivial size problem for the Laplacian you definitely want to use multigrid. You can start by trying algebraic multigrid on both cases with
-pc_type gamg Barry On Sep 22, 2014, at 6:41 PM, Alletto, John M <[email protected]> wrote: > I am solving one of the PETSc 3D Laplacian examples with a 7 point stencil of > width 1 and in a separate baseline with a 13 point stencil of width 2 (a more > accurate mesh). > > What worked fast in terms of solvers and pre-conditioner for the less > accurate baseline was non-optimal (very slow) for the more accurate baseline. > > Are there a set of general rules for picking preconditioners and solvers when > solving a 3D Laplace's equation? > > > Thank you for your time > John Alletto
