-da_refine $DAREFINE determines how large the final problem will be. By default if you don't supply pc_mg_levels then it uses $DAREFINE + 1 as the number of levels of MG to use; for example -da_refine 1 would result in 2 levels of multigrid.
> On Mar 30, 2017, at 2:17 PM, Justin Chang <[email protected]> wrote: > > Hi all, > > Just a general conceptual question: say I am tinkering around with SNES > ex48.c and am running the program with these options: > > mpirun -n $NPROCS -pc_type mg -M $XSEED -N $YSEED -P $ZSEED -thi_mat_type > baij -da_refine $DAREFINE -pc_mg_levels $MGLEVELS > > I am not too familiar with mg, but it seems to me there is a very strong > correlation between $MGLEVELS and $DAREFINE as well as perhaps even the > initial coarse grid size (provided by $X/YZSEED). > > Is there a rule of thumb on how these parameters should be? I am guessing it > probably is also hardware/architectural dependent? > > Thanks, > Justin
