[petsc-users] Question about MatGetRow

[Matthew Knepley]

On Fri, Feb 3, 2023 at 9:04 AM 김성익 <ksi2443 at gmail.com> wrote:

> 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.
>

Did you run and see what you get? If it is on all processes, it should work.

  Thanks,

     Matt


> Hyung Kim
>
>
>
>
>
>
>
> 2023년 2월 3일 (금) 오후 10:54, Matthew Knepley <knepley at gmail.com>님이 작성:
>
>> On Fri, Feb 3, 2023 at 8:52 AM 김성익 <ksi2443 at 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 at gmail.com>님이 작성:
>>>
>>>> On Fri, Feb 3, 2023 at 8:45 AM 김성익 <ksi2443 at gmail.com> wrote:
>>>>
>>>>> Following your comments,
>>>>> If I extract first row of below matrix.
>>>>> [image: 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 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/>
>>>>>>
>>>>>
>>>>
>>>> --
>>>> 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/>
>>>>
>>>
>>
>> --
>> 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/>
>>
>

-- 
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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