Hmmm ./ex19 -da_refine 2 -pc_type gamg -help | grep mg_coarse | grep shift -mg_coarse_sub_pc_factor_shift_type <INBLOCKS> (choose one of) NONE NONZERO POSITIVE_DEFINITE INBLOCKS (PCFactorSetShiftType) -mg_coarse_sub_pc_factor_shift_amount <2.22045e-14>: Shift added to diagonal (PCFactorSetShiftAmount)
What do you get with -ksp_type gmres -pc_type gamg -help | grep factor_shift ? What do you get with -ksp_type gmres -pc_type gamg -mg_coarse_sub_pc_factor_shift_type gibberish ? You should get an error message saying it doesn't know the type. Otherwise it is not checking that option. Or perhaps you somehow have it set to use a LU factorization that doesn't support this option like SuperLU. Barry > On Sep 19, 2015, at 6:10 PM, Gideon Simpson <[email protected]> wrote: > > It gives zero pivots on: > > -ksp_type gmres -pc_type gamg -mg_coarse_sub_pc_factor_shift_type NONZERO > > It has no problem with: > > -ksp_type gmres -pc_type bjacobi -sub_pc_factor_shift_type NONZERO > > -gideon > >> On Sep 19, 2015, at 12:37 AM, Barry Smith <[email protected]> wrote: >> >> >>> On Sep 18, 2015, at 10:42 PM, Gideon Simpson <[email protected]> >>> wrote: >>> >>> I’m getting a zero pivot in LU factorization error when I use the gamg >>> preconditioner. I know there is some issue with my matrix, as I get the >>> same error if I use pc_type lu in serial, or if I use pc_type bjacobi in >>> parallel, both of which are corrected by adding -pc_factor_shift_type >>> NONZERO -sub_pc_factor_shift_type NONZERO, respectively. However, I can’t >>> quite seem to figure out the analogous command to use for the gamg >>> preconditioner. >> >> You need to figure out the prefix to the option that is added by gamg to set >> it. One way is to run with the gamg options and -help and grep for >> factor_shift. >> >> The option is like something like -mg_coarse_pc_factor_shift_type nonzero >> or -mg_coarse_sub_pc_factor_shift_type >> >> Barry >> >>> >>> -gideon >>> >> >
