[petsc-users] Question about MatGetRow

[김성익]

Following your comments,
If I extract first row of below matrix.
[image: image.png]
IS isrow;
PetscInt *indices;
PetscMalloc1(1, *indices);
Indices[0] = 0;
ISCreateGenreral(PETSC_COMM_WORLD, 1, indices, PETSC_COPY_VALUES, &isrow);
MatCreateSubMatrix(mat,isrow,NULL,MAT_INITIAL_MATRIX,&newmat);

Then can I get the array about first row of global matrix in all processes?

Hyung Kim

2023년 2월 3일 (금) 오후 10:26, Matthew Knepley <knepley at gmail.com>님이 작성:

> On Fri, Feb 3, 2023 at 8:06 AM 김성익 <ksi2443 at gmail.com> wrote:
>
>> Following your comments,
>> I want to check below things.
>> For example, the global dense matrix are as below.
>> [image: image.png]
>> If I want to get first row ('1 2 0 0 3 0 0 4') in Proc 1.
>> Then I should put 'MatCreateSubMatrix
>> <https://petsc.org/main/docs/manualpages/Mat/MatCreateSubMatrix/>(mat,
>> isrow, NULL, MAT_INITIAL_MATRIX, *&*newmat)'
>> and isrow will be [0 1 2 3 4 5 6 7].
>>
>> In this case, How can I make isrow?
>> Actually I can't understand the procedure of handling isrow.
>>
>
> You create an IS object of type ISGENERAL and give it the array of global
> indices that you want to extract.
>
>   Thanks,
>
>      Matt
>
>
>> Hyung Kim
>>
>> 2023년 2월 3일 (금) 오후 9:03, Mark Adams <mfadams at lbl.gov>님이 작성:
>>
>>> https://petsc.org/main/docs/manualpages/Mat/MatCreateSubMatrix/
>>>
>>> Note, PETSc lets you give NULL arguments if there is a reasonable
>>> default.
>>> In this case give NULL for the column IS and you will get the whole
>>> columns.
>>>
>>> Mark
>>>
>>> On Fri, Feb 3, 2023 at 4:05 AM 김성익 <ksi2443 at gmail.com> wrote:
>>>
>>>> Hello,
>>>>
>>>>
>>>> By using MatGetRow, user can get vectors from local matrix (at each
>>>> process).
>>>>
>>>> However, I need other process's row values.
>>>> So I have 2 questions.
>>>>
>>>> 1. Is there any function for getting arrays from other process's??
>>>>
>>>> 2. Or is there any function like matrix version of vecscattertoall??
>>>>
>>>> Thanks,
>>>> Hyung Kim
>>>>
>>>
>
> --
> 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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