[petsc-users] Accessing Vector's ghost values

Matthew Knepley knepley at gmail.com
Thu Feb 23 10:53:03 CST 2012

On Thu, Feb 23, 2012 at 10:46 AM, Bojan Niceno <bojan.niceno at psi.ch> wrote:

> Hi all,
> I've never used a mailing list before, so I hope this message will reach
> PETSc users and experts and someone might be willing to help me.  I am also
> novice in PETSc.
> I have developed an unstructured finite volume solver on top of PETSc
> libraries.  In sequential, it works like a charm.  For the parallel
> version, I do domain decomposition externally with Metis, and work out
> local and global numberings, as well as communication patterns between
> processor.  (The latter don't seem to be needed for PETSc, though.)  When I
> run my program in parallel, it also works, but I miss values in vectors'
> ghost points.
> I create vectors with command: VecCreate(PETSC_COMM_WORLD, &x);
> Is it possible to get the ghost values if a vector is created like this?

I do not understand this question. By definition, "ghost values" are those
not stored in the global vector.

> I have tried to use VecCreateGhost, but for some reason which is beyond my
> comprehension, PETSc goes berserk when it reaches the command:
> VecCreateGhost(PETSC_COMM_**WORLD, n, PETSC_DECIDE, nghost, ifrom, &x)

I think you can understand that "berserk" tells me absolutely nothing.
Error message? Stack trace? Did you try to run an
example which uses VecGhost?



> Can anyone help me?  Either how to reach ghost values for vector created
> by VecCreate, or how to use VecCreateGhost properly?
>   Kind regards,
>   Bojan

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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