[petsc-users] doubts on VecScatterCreate

[Emmanuel Ayala]

Hi,

Thank you very much for the help and the quickly answer.

After check my code the problem was previous to scattering. *The scatter
routines work perfectly.*

Just to undesrtand, in the line:

ISCreateStride(MPI_COMM_WORLD,(end-start),start,1,&is_fromA);

if I use MPI_COMM_WORLD, it means that all the processes have a copy of the
(current local process) index set?
If I use MPI_COMM_SELF, it means that only the local process have
information about the index set?

Kind regards



El lun., 4 de nov. de 2019 a la(s) 08:47, Smith, Barry F. (
bsmith at mcs.anl.gov) escribió:

>
>    It works for me. Please send a complete code that fails.
>
>
>
>
> > On Nov 3, 2019, at 11:41 PM, Emmanuel Ayala via petsc-users <
> petsc-users at mcs.anl.gov> wrote:
> >
> > Hi everyone, thanks in advance.
> >
> > I have three parallel vectors: A, B and C. A and B have different sizes,
> and C must be contain these two vectors (MatLab notation C=[A;B]). I need
> to do some operations on C then put back the proper portion of C on A and
> B, then I do some computations on A and B y put again on C, and the loop
> repeats.
> >
> > For these propose I use Scatters:
> >
> > C is created as a parallel vector with size of (sizeA + sizeB) with
> petsc_decide for parallel layout. The vectors have been distributed on the
> same amount of processes.
> >
> > For the specific case with order [A;B]
> >
> > VecGetOwnershipRange(A,&start,&end);
> > ISCreateStride(MPI_COMM_WORLD,(end-start),start,1,&is_fromA);
> > ISCreateStride(MPI_COMM_WORLD,(end-start),start,1,&is_toC1);// this is
> redundant
> > VecScatterCreate(A,is_fromA,C,is_toC1,&scatter1);
> >
> > VecGetSize(A,&sizeA)
> > VecGetOwnershipRange(B,&start,&end);
> > ISCreateStride(MPI_COMM_WORLD,(end-start),start,1,&is_fromB);
> > ISCreateStride(MPI_COMM_WORLD,(end-start),(start+sizeA),1,&is_toC2);
> //shifts the index location
> > VecScatterCreate(B,is_fromB,C,is_toC2,&scatter2);
> >
> > Then I can use
> > VecScatterBegin(scatter1,A,C,INSERT_VALUES,SCATTER_FORWARD);
> > VecScatterEnd(scatter1,A,C,INSERT_VALUES,SCATTER_FORWARD);
> >
> > and
> > VecScatterBegin(scatter1,C,A,INSERT_VALUES,SCATTER_REVERSE);
> > VecScatterEnd(scatter1,C,A,INSERT_VALUES,SCATTER_REVERSE);
> >
> > and the same with B.
> > I used MPI_COMM SELF and I got the same results.
> >
> > The situation is: My results look good for the portion of B, but no for
> the portion of A, there is something that I'm doing wrong with the
> scattering?
> >
> > Best regards.
>
>
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