[petsc-users] Vecscatter question

[Jed Brown]

On Mon, Aug 29, 2011 at 20:32, Tabrez Ali <stali at geology.wisc.edu> wrote:

> If during Vecscatter (say from a global vector x to a local vector y) if
> 'is' and 'iy' are such that almost all values being scattered happen to be
> on the local proc then almost 0 or very little MPI calls would be made
> internally. Is this correct?
>

Very few values would be sent anywhere. The number of MPI calls depends on
the number of processes that need to receive values and the scatter method
(methods descriptions:
http://www.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-dev/docs/manualpages/Vec/VecScatterCreate.html
).
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