> > > Diffusion is as "nice" as possible in terms of stability and > well-established theory, multigrid will normally work very well. In > the latest release of PETSc, you could try -pc_type gamg. > Otherwise/alternatively, configure using --download-ml or > --download-hypre, then run with -pc_type ml or -pc_type hypre.
Thanks for your reply. Do you have experience with lumping of the mass matrix? The following options semm to work fine if I don't use lumping: mpiexec -np 4 ./ThermoPaine3d-opt -ksp_type fgmres -pc_type ksp -ksp_ksp_type cg -ksp_pc_type jacobi -ksp_monitor_true_residual -ksp_converged_reason (any comments to the options???) However, for heat diffusion, especially for non-steady starting conditions, oscillations seem to be a common problem (AFAIK). If I apply lumping of the mass matrix - which means I put the row-sum of the mass matrix on the main diagonal - the solver doesn't converge any more. Before it converged after 2 to 5 iterations, now I was running several hundreds. Maybe some of you - definitely more experienced users - have some ideas/suggestions? P.S.: I have tried a lot of different combinations of solvers and preconditioners (including those of the last reply).. Thank you, Robert
