[petsc-users] KSP changes for successive solver

Matthew Knepley knepley at gmail.com
Sat Jul 18 21:56:23 CDT 2015

On Sat, Jul 18, 2015 at 9:53 PM, Michele Rosso <mrosso at uci.edu> wrote:

>  Barry,
> I tried the master branch of PETSc as you suggested and unfortunately the
> problem with KSP being set to GMRES on the coarse level when using
> "-mg_coarse_ksp_type preonly"  is still there. I attached the output from
> ksp view and the options stack.
> Am I missing something?

If you show output from -log_summary we can make sure you are running the
version we expect.



> Thanks,
> Michele
> On Thu, 2015-07-16 at 17:30 -0500, Barry Smith wrote:
>    Michel,
>     This is a very annoying feature that has been fixed in master http://www.mcs.anl.gov/petsc/developers/index.html  I would like to have changed it in maint but Jed would have a shit-fit :-) since it changes behavior.
>   Barry
> > On Jul 16, 2015, at 4:53 PM, Michele Rosso <mrosso at uci.edu> wrote:> > Hi,> > I am performing a series of solves inside a loop. The matrix for each solve changes but not enough to justify a rebuilt of the PC at each solve.> Therefore I am using  KSPSetReusePreconditioner to avoid rebuilding unless necessary. The solver is CG + MG with a custom  PC at the coarse level.> If KSP is not updated each time, everything works as it is supposed to. > When instead I allow the default PETSc  behavior, i.e. updating PC every time the matrix changes, the coarse level KSP , initially set to PREONLY, is changed into GMRES > after the first solve. I am not sure where the problem lies (my PC or PETSc), so I would like to have your opinion on this.> I attached the ksp_view for the 2 successive solve and the options stack.> > Thanks for your help,> Michel> > > > <ksp_view.txt><petsc_options.txt>

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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