Actually in the last mail, below scripts are running in all processes.

IS isrow;
PetscInt *indices;
PetscMalloc1(1, &indices);
Indices[0] = 0;
ISCreateGenreral(PETSC_COMM_WORLD, 1, indices, PETSC_OWN_POINTER, &isrow);
MatCreateSubMatrix(mat,isrow,NULL,MAT_INITIAL_MATRIX,&newmat);
(extract from newmat)

However, you said it cannot get the values of first row of global matrix.
Please let me know how can I fix this scripts for getting the 1st row of global matrix in all processes.

Hyung Kim







2023년 2월 3일 (금) 오후 10:54, Matthew Knepley <knepley@gmail.com>님이 작성:
On Fri, Feb 3, 2023 at 8:52 AM 김성익 <ksi2443@gmail.com> wrote:
I want to extract same row values of global matrix in all processes.
Then how can I do this??

Create the same IS on each process.

  THanks,

    Matt
 
The case of same problem of vector, I just use vecscattertoall.
However, I can't find same function for matrix.

Hyung Kim

2023년 2월 3일 (금) 오후 10:47, Matthew Knepley <knepley@gmail.com>님이 작성:
On Fri, Feb 3, 2023 at 8:45 AM 김성익 <ksi2443@gmail.com> wrote:
Following your comments,
If I extract first row of below matrix.
image.png
IS isrow;
PetscInt *indices;
PetscMalloc1(1, *indices);

That should be &indices.
 
Indices[0] = 0;
ISCreateGenreral(PETSC_COMM_WORLD, 1, indices, PETSC_COPY_VALUES, &isrow);

You should use PETSC_OWN_POINTER.
 
MatCreateSubMatrix(mat,isrow,NULL,MAT_INITIAL_MATRIX,&newmat);

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

No, just on the process which gives 0. If you do that on every process, every rank with get row 0.

  Thanks,

     Matt
 
Hyung Kim

2023년 2월 3일 (금) 오후 10:26, Matthew Knepley <knepley@gmail.com>님이 작성:
On Fri, Feb 3, 2023 at 8:06 AM 김성익 <ksi2443@gmail.com> wrote:
Following your comments,
I want to check below things.
For example, the global dense matrix are as below.
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(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@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@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



--
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



--
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