On 25 July 2018 at 09:48, Matthew Knepley <knep...@gmail.com> wrote: > On Wed, Jul 25, 2018 at 4:24 AM Buesing, Henrik < > hbues...@eonerc.rwth-aachen.de> wrote: > >> Dear all, >> >> I would like to improve the iterative solver [1]. As I understand it I >> would need to improve the preconditioner for the Schur complement. >> >> How would I do that? >> > > 1) I always start from the exact thing (full Schur factorization with > exact solves and back off parts until I am happy) > > 2) Is the a11 block a good preconditioner for your Schur complement? If > not, I would start by replacing that matrix > with something better. >
Some additional info. If you want to pursue option 2, you need to do call PCFieldSplitSetSchurPre() http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/PC/ PCFieldSplitSetSchurPre.html#PCFieldSplitSetSchurPre with PC_FIELDSPLIT_SCHUR_PRE_USER <http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/PC/PCFieldSplitSchurPreType.html#PCFieldSplitSchurPreType> (second arg) and your user defined schur complement preconditioner (last arg). Thanks, Dave > > Thanks, > > Matt > > >> Thank you for your help! >> Henrik >> >> >> >> [1] >> -ksp_max_it 100 -ksp_rtol 1e-6 -ksp_atol 1e-50 -ksp_type fgmres -pc_type >> fieldsplit -pc_fieldsplit_type schur -pc_fieldsplit_schur_precondition >> a11 -fieldsplit_p_w_ksp_type preonly -fieldsplit_S_n_ksp_type gmres >> -fieldsplit_p_w_pc_type hypre -fieldsplit_p_w_pc_hypre_type boomeramg >> -fieldsplit_S_n_pc_type hypre -fieldsplit_S_n_pc_hypre_type boomeramg >> -fieldsplit_S_n_ksp_max_it 100 fieldsplit_S_n_ksp_rtol 1e-2 >> >> >> -- >> Dipl.-Math. Henrik Büsing >> Institute for Applied Geophysics and Geothermal Energy >> E.ON Energy Research Center >> RWTH Aachen University >> >> Mathieustr. 10 >> <https://maps.google.com/?q=Mathieustr.+10&entry=gmail&source=g> >> | Tel +49 (0)241 80 49907 >> 52074 Aachen, Germany | Fax +49 (0)241 80 49889 >> >> http://www.eonerc.rwth-aachen.de/GGE >> hbues...@eonerc.rwth-aachen.de >> >> > > -- > What most experimenters take for granted before they begin their > experiments is infinitely more interesting than any results to which their > experiments lead. > -- Norbert Wiener > > https://www.cse.buffalo.edu/~knepley/ <http://www.caam.rice.edu/~mk51/> >
