[francois pacull] Re: fieldsplits

[Matthew Knepley]

On Thu, Dec 10, 2009 at 3:03 PM, Jed Brown <jed at 59a2.org> wrote:

> Can KSPView before KSPSolve reasonably be made to work?
>

What breaks? If you mean that it is not broken, but information is different
than it
is after KSPSetUp(), I would say no.

  matt


> ---------- Forwarded message ----------
> From: francois pacull <fpacull at fluorem.com>
> To: Jed Brown <jed at 59a2.org>
> Date: Thu, 10 Dec 2009 12:27:57 +0100
> Subject: Re: fieldsplits
> Thanks a lot, it works now.
>
> Besides my confusion with the fieldsplit Schur options, I think that my
> mistake was that I was not calling a PCSetUp of the fieldsplit PC before
> calling a KSPView (which I always call just before the KSPSolve):
> PCFieldSplitSetType(fieldsplitPC,PC_COMPOSITE_SCHUR) ...
> PCSetUp(fieldsplitPC), KSPView, KSPSolve works
> PCFieldSplitSetType(fieldsplitPC,PC_COMPOSITE_SCHUR) ... KSPSolve works
> PCFieldSplitSetType(fieldsplitPC,PC_COMPOSITE_SCHUR) ... KSPView,
> KSPSolve does not work.
>
> francois.
>
>
> Jed Brown a écrit :
> > Thanks for the info, I'll read the rest more carefully later.
> >
> > On Wed, 09 Dec 2009 16:56:11 +0100, francois pacull <fpacull at fluorem.com>
> wrote:
> >
> >
> >> I would like to use an ILU factorization for A, a GMRES for S... Also, I
> >> would like an ILU factorization for D,  in order to construct a
> >> preconditioner for S, but how to set it up? With fieldsplit_1 I guess?
> >>
> >
> > I think this will do what you're asking for
> >
> > -fieldsplit_0_ksp_type preonly         # no subcycles on A
> > -fieldsplit_0_pc_type ilu              # precondition A using ILU
> > -pc_fieldsplit_schur_precondition diag # use D as preconditioning matrix
> for S
> > -fieldsplit_1_ksp_type gmres           # GMRES on S
> > -fieldsplit_1_ksp_max_it 10            # 10 iterations max
> > -fieldsplit_1_pc_type ilu              # ILU of D to precondition GMRES
> on S
> >
> > Use -ksp_type fgmres because the preconditioner is nonlinear, pc_types
> > would need to be asm or bjacobi in parallel, but try in serial first.
> >
> > Jed
> >
> >
>
>


-- 
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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