On Fri, 16 Apr 2010 13:51:13 +0200, tribur at vision.ee.ethz.ch wrote: > ML works now using, e.g., -mg_coarse_redundant_pc_factor_shift_type > POSITIVE_DEFINITE. However, it converges very slowly using the default > REDUNDANT for the coarse solve.
"Converges slowly" or "the coarse-level solve is expensive"? I suggest starting with -mg_coarse_pc_type lu -mg_coarse_pc_factor_mat_solver_package mumps or varying parameters in ML to see if you can make the coarse level problem smaller without hurting convergence rate. You can do semi-redundant solves if you scale processor counts beyond what MUMPS works well with. Depending on what problem you are solving, ML could be producing a (nearly) singular coarse level operator in which case you can expect very confusing and inconsistent behavior. Jed
