And why are you fixed on 5 levels? On Wednesday, 2 October 2013, Barry Smith wrote:
> > Something is wrong, you should be getting better convergence. Please > answer my other email. > > > On Oct 2, 2013, at 1:10 PM, Michele Rosso <[email protected] <javascript:;>> > wrote: > > > Thank you all for your contribution. > > So far the fastest solution is still the initial one proposed by Jed in > an earlier round: > > > > -ksp_atol 1e-9 -ksp_monitor_true_residual -ksp_view -log_summary > -mg_coarse_pc_factor_mat_solver_package superlu_dist > > -mg_coarse_pc_type lu -mg_levels_ksp_max_it 3 -mg_levels_ksp_type > richardson -options_left -pc_mg_galerkin > > -pc_mg_levels 5 -pc_mg_log -pc_type mg > > > > where I used -mg_levels_ksp_max_it 3 as Barry suggested instead of > -mg_levels_ksp_max_it 1. > > I attached the diagnostics for this case. Any further idea? > > Thank you, > > > > Michele > > > > > > On 10/01/2013 11:44 PM, Barry Smith wrote: > >> On Oct 2, 2013, at 12:28 AM, Jed Brown <[email protected]<javascript:;>> > wrote: > >> > >>> "Mark F. Adams" <[email protected] <javascript:;>> writes: > >>>> run3.txt uses: > >>>> > >>>> -ksp_type richardson > >>>> > >>>> This is bad and I doubt anyone recommended it intentionally. > >> Hell this is normal multigrid without a Krylov accelerator. Under > normal circumstances with geometric multigrid this should be fine, often > the best choice. > >> > >>> I would have expected FGMRES, but Barry likes Krylov smoothers and > >>> Richardson is one of a few methods that can tolerate nonlinear > >>> preconditioners. > >>> > >>>> You also have, in this file, > >>>> > >>>> -mg_levels_ksp_type gmres > >>>> > >>>> did you or the recommenders mean > >>>> > >>>> -mg_levels_ksp_type richardson ??? > >>>> > >>>> you are using gmres here, which forces you to use fgmres in the outer > solver. This is a safe thing to use you if you apply your BCa > symmetrically with a low order discretization then > >>>> > >>>> -ksp_type cg > >>>> -mg_levels_ksp_type richardson > >>>> -mg_levels_pc_type sor > >>>> > >>>> is what I'd recommend. > >>> I thought that was tried in an earlier round. > >>> > >>> I don't understand why SOR preconditioning in the Krylov smoother is so > >>> drastically more expensive than BJacobi/ILU and why SOR is called so > >>> many more times even though the number of outer iterations > >>> > >>> bjacobi: PCApply 322 1.0 4.1021e+01 1.0 6.44e+09 1.0 > 3.0e+07 1.6e+03 4.5e+04 74 86 98 88 92 28160064317351226 20106 > >>> bjacobi: KSPSolve 46 1.0 4.6268e+01 1.0 7.52e+09 1.0 > 3.0e+07 1.8e+03 4.8e+04 83100100 99 99 31670065158291309 20800 > >>> > >>> sor: PCApply 1132 1.0 1.5532e+02 1.0 2.30e+10 1.0 > 1.0e+08 1.6e+03 1.6e+05 69 88 99 88 93 21871774317301274 18987 > >>> sor: KSPSolve 201 1.0 1.7101e+02 1.0 2.63e+10 1.0 > 1.1e+08 1.8e+03 1.7e+05 75100100 99 98 24081775248221352 19652 > >> > > > > <best.txt> > >
