[petsc-users] doubts on VecScatterCreate

[Emmanuel Ayala]

Ok, thanks for the clarification.

Kind regards.

El vie., 8 de nov. de 2019 a la(s) 04:23, Matthew Knepley (knepley at gmail.com)
escribió:

> On Fri, Nov 8, 2019 at 2:23 AM Emmanuel Ayala via petsc-users <
> petsc-users at mcs.anl.gov> wrote:
>
>> 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?
>>
>
> No, each process has whatever you give it in this call. The comm
> determines what happens with collective calls, like
>
>
> https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/IS/ISGetTotalIndices.html
>
>   Thanks,
>
>     Matt
>
>
>> 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.
>>>
>>>
>
> --
> 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
>
> https://www.cse.buffalo.edu/~knepley/
> <http://www.cse.buffalo.edu/~knepley/>
>
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