[petsc-users] question about arbitrary eigenvector selection in SLEPC

[Matthew Knepley]

On Thu, May 29, 2014 at 10:58 AM, Giacomo Mulas <gmulas at oa-cagliari.inaf.it>
wrote:

> On Thu, 29 May 2014, Matthew Knepley wrote:
>
>  There might be an easier way to do this:
>>   PetscScalar val = 0.0, gval;
>>
>>   VecGetOwnershipRange(xr, &low, &high);
>>   if ((myindex >= low) && (myindex < high)) {
>>     VecGetArray(localx1,&a);
>>     val = a[myindex-low];
>>     VecRestoreArray(localx1, &a);
>>   }
>>   MPI_Allreduce(&val, &gval, 1, MPIU_SCALAR, MPI_SUM, PETSC_COMM_WORLD);
>>
>> Now everyone has the value at myindex.
>>
>
> brilliant, why didn't I think of this? Only, I guess you were
> copying/pasting and some variable names slipped, namely localx instead of
> xr.  Should it be
>

Yes

   Matt


>   PetscScalar val = 0.0, gval;
>   PetscScalar *a;
>
>   VecGetOwnershipRange(xr, &low, &high);
>   if ((myindex >= low) && (myindex < high)) {
>     VecGetArray(xr,&a);
>     val = a[myindex-low];     VecRestoreArray(xr, &a);
>   }
>   MPI_Allreduce(&val, &gval, 1, MPIU_SCALAR, MPI_SUM, PETSC_COMM_WORLD);
>   *rr = gval*gval;
>   *ri = 0;
>
> ?
>
> Thanks!
> Giacomo
>
> --
> _________________________________________________________________
>
> Giacomo Mulas <gmulas at oa-cagliari.inaf.it>
> _________________________________________________________________
>
> INAF - Osservatorio Astronomico di Cagliari
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>
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>
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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.
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