[petsc-users] Correlation between da_refine and pg_mg_levels

[Matthew Knepley]

On Thu, Mar 30, 2017 at 2:17 PM, Justin Chang <jychang48 at gmail.com> 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?
>

You cannot refine further than 1 grid point in any direction. Moreover,
DMDA has some problems with MG on grids without an odd number of vertices I
think.

   Matt


> Thanks,
> Justin
>



-- 
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
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