[petsc-users] Use of PCFieldSplitSetSchurPre

[Mark Adams]

On Thu, Aug 21, 2014 at 2:11 PM, Jed Brown <jed at jedbrown.org> wrote:

> Mark Adams <mfadams at lbl.gov> writes:
>
> > I have fixed this by setting the KSP op:
> >
> >        call PCFieldSplitGetSubKSP(spc,i,subksp,ierr)
> >        call KSPSetOperators(subksp(2),solver%schur,solver%schur,ierr)
>
> Mark, where is the information getting lost?  If the interface does not
> work correctly, we (PETSc) need to fix the interface, not just find a
> workaround.  That's why I suggested running in a debugger.
>

OK, I'll look at it but I need to get the debug build error (other thread)
fixed to be able to step through the code.  That error happens before this
PC Schur stuff is set.


>
> > Thanks,
> >
> >
> >
> > On Tue, Aug 19, 2014 at 8:17 AM, Jed Brown <jed at jedbrown.org> wrote:
> >
> >> Mark Adams <mfadams at lbl.gov> writes:
> >>
> >> > I am creating an Schur complement matrix explicitly (solver%schur) and
> >> > setting it with code like:
> >> >
> >> > call SNESGetKSP(solver%snes,innerksp,ierr)
> >> > call KSPGetPC(innerksp,spc,ierr)
> >> > call
> >> >
> >>
> PCFieldSplitSetSchurPre(spc,PC_FIELDSPLIT_SCHUR_PRE_USER,solver%schur,ierr)
> >> >
> >> > I would think that the "inner" solver would not be used but it is
> getting
> >> > used.
> >>
> >> [...]
> >>
> >> > PC Object:(fsa_) 4 MPI processes
> >> >   type: fieldsplit
> >> >     FieldSplit with Schur preconditioner, factorization FULL
> >> >     Preconditioner for the Schur complement formed from A11
> >>
> >> I would set a breakpoint at PCFieldSplitSetSchurPre_FieldSplit and then
> >> watch -l jac->schurpre since it appears that your information is being
> >> lost somewhere.
> >>
>
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