On Oct 2, 2013, at 12:28 AM, Jed Brown <[email protected]> wrote:
> "Mark F. Adams" <[email protected]> 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
