[petsc-users] gmres restart

[Barry Smith]

On Nov 29, 2010, at 6:01 PM, Verena Kuhlemann wrote:

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> On Mon, Nov 29, 2010 at 6:08 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
> 
> On Nov 29, 2010, at 5:04 PM, Verena Kuhlemann wrote:
> 
> > Hello,
> >
> > I have a (hopefully) quick question about setting the restart for gmres.
> >
> > I set the restart to be 50, but when I use KSPView it looks like GMRES
> > still uses a restart of 30. It is possible that I overwrite my settings
> > somehow? Here is the relevant part of my code:
> >
> > KSPCreate(PETSC_COMM_WORLD,&ksp);
> > KSPSetOperators(ksp,A,A,DIFFERENT_NONZERO_PATTERN);
> 
>   KSPSetType(ksp,KSPGMRES);
> 
> > KSPGMRESSetRestart(ksp,50);
> 
>   You have not set the type to GMRES by this point, therefor the setting of restart is ignored. Must set the type before this.
> 
> Ah, I thought I don't have to set it, since GMRES is the default. Now it works, thanks.

   The thing is it delays picking the default as long as possible, thus it was not set at that point. But you are right, it would be reasonable to be known the whole time.

   Barry

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>   BTW: we highly recommend just calling KSPSetFromOptions() and setting parameters from the options database, much nicer IOHO then hardwiring in the source code.
> 
>   Barry
> 
> 
> > KSPSetInitialGuessNonzero(ksp,PETSC_TRUE);
> > KSPSetTolerances(ksp,1.e-12,1.e-12,PETSC_DEFAULT,100000);
> > KSPSetUp(ksp);
> > KSPGetPC(ksp,&pc);
> > PCSetType(pc,PCNONE);
> > KSPView(ksp,PETSC_VIEWER_STDOUT_WORLD);
> > KSPSolve(ksp,b,x);
> >
> >
> > Thanks,
> > Verena
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> 
> -- 
> Verena Kuhlemann
> Ph.D. Candidate
> Mathematics and Computer Science Department
> Emory University
>