[petsc-users] How to solve the pressure possion equations with four neuman bc

[Matthew Knepley]

On Sun, Sep 25, 2016 at 4:06 AM, 丁老师 <ztdepyahoo at 163.com> wrote:

> Dear professor:
>      In the ksp example ex50.c, i do not understand the meaning of
> *KSPSolve*
> <http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/KSP/KSPSolve.html#KSPSolve>
> *(ksp,NULL,NULL);*
>
> *     n**MatNullSpaceCreate* <http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatNullSpaceCreate.html#MatNullSpaceCreate>*(**PETSC_COMM_WORLD* <http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Sys/PETSC_COMM_WORLD.html#PETSC_COMM_WORLD>*,**PETSC_TRUE* <http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Sys/PETSC_TRUE.html#PETSC_TRUE>*,0,0,&nullspace);  *
>
>        What is the meaning of NULL in the kspsolve. and two "0" in the
> MatNullSpaceCrea
> <http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatNullSpaceCreate.html#MatNullSpaceCreate>
> te.
>

1) The NULL for KSPSolve() means that


http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/KSP/KSPSetComputeOperators.html

http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/KSP/KSPSetComputeRHS.html#KSPSetComputeRHS

are used to make the problem.

2) The NullSpace is the space of constant functions with these arguments


  Matt

Regards
>
>
>
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>
> At 2016-09-24 00:25:09, "Jed Brown" <jed at jedbrown.org> wrote:
> >"Kong, Fande" <fande.kong at inl.gov> writes:
> >
> >> Any references on this topic except the users manual?  I am interested in
> >> mathematics theory on this topic.
> >
> >These are relevant. I've only skimmed them briefly, but they might
> >suggest ways to improve PETSc's handling of singular systems.  The
> >technique is ancient.
> >
> >https://doi.org/10.1137/S0895479803437803
> >
> >https://doi.org/10.1007/s10543-009-0247-7
>
>
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>



-- 
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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