[petsc-users] Use of PCFieldSplitSetSchurPre

[Jed Brown]

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.

> 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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