[petsc-users] about VecScatterCreate()

[Matthew Knepley]

On Fri, May 28, 2010 at 1:02 PM, Yujie <recrusader at gmail.com> wrote:

> Dear PETSc Developers,
>
> I got the following information from VecScatterCreate() manpage.
> "
> PetscErrorCode  VecScatterCreate(Vec xin,IS ix,Vec yin,IS iy,VecScatter
> *newctx)
>
> Collective on Vec
>
> Input Parameters
>        xin     - a vector that defines the shape (parallel data layout of
> the
> vector) of vectors from which we scatter
>        yin     - a vector that defines the shape (parallel data layout of
> the
> vector) of vectors to which we scatter
>        ix      - the indices of xin to scatter (if PETSC_NULL scatters all
> values)
>        iy      - the indices of yin to hold results (if PETSC_NULL fills
> entire
> vector yin)
> "
> My question is about "ix". If xin and yin are parallel Vec, how about ix?
>
> Is "ix"  an IS only containing local index set or a parallel IS
> containing all the index set on all the processors (each local index
> set on its processor)? Thanks a lot.
>

ix contains some indices for that process. The indices can be different on
each process.
We take the union.

   Matt


> Regards,
> Yujie
>



-- 
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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