[petsc-users] Vecscatter question

[Matthew Knepley]

On Tue, Aug 30, 2011 at 1:36 AM, Jed Brown <jedbrown at mcs.anl.gov> wrote:

> 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
> ).
>

Also, you can make an event around these calls and get information on the
number of messages and the average size.

   Matt

-- 
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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