[petsc-users] parallel computing error

[Barry Smith]

  The code in ex125.c contains

 PetscCall(MatCreate(PETSC_COMM_WORLD, &C));
  PetscCall(MatSetOptionsPrefix(C, "rhs_"));
  PetscCall(MatSetSizes(C, m, PETSC_DECIDE, PETSC_DECIDE, nrhs));
  PetscCall(MatSetType(C, MATDENSE));
  PetscCall(MatSetFromOptions(C));
  PetscCall(MatSetUp(C));

This dense parallel matrix is suitable for passing to MatMatSolve() as the right-hand side matrix. Note it is created with PETSC_COMM_WORLD and its type is set to be MATDENSE.

  You may need to make a sample code by stripping out all the excess code in ex125.c to just create an MATAIJ and MATDENSE and solves with MatMatSolve() to determine why you code does not work.



> On May 4, 2023, at 3:20 AM, ­권승리 / 학생 / 항공우주공학과 <ksl7912 at snu.ac.kr> wrote:
> 
> Dear Barry Smith
> 
> Thank you for your reply.
> 
> I've already installed MUMPS.
> 
> And I checked the example you said (ex125.c), I don't understand why the RHS matrix becomes the SeqDense matrix.
> 
> Could you explain in more detail?
> 
> Best regards
> Seung Lee Kwon
> 
> 2023년 5월 4일 (목) 오후 12:08, Barry Smith <bsmith at petsc.dev <mailto:bsmith at petsc.dev>>님이 작성:
>> 
>>   You can configure with MUMPS ./configure --download-mumps --download-scalapack --download-ptscotch --download-metis --download-parmetis 
>> 
>>   And then use MatMatSolve() as in src/mat/tests/ex125.c with parallel MatMatSolve() using MUMPS as the solver.
>> 
>>   Barry
>> 
>> 
>>> On May 3, 2023, at 10:29 PM, ­권승리 / 학생 / 항공우주공학과 <ksl7912 at snu.ac.kr <mailto:ksl7912 at snu.ac.kr>> wrote:
>>> 
>>> Dear developers
>>> 
>>> Thank you for your explanation.
>>> 
>>> But I should use the MatCreateSeqDense because I want to use the MatMatSolve that B matrix must be a SeqDense matrix.
>>> 
>>> Using MatMatSolve is an inevitable part of my code.
>>> 
>>> Could you give me a comment to avoid this error?
>>> 
>>> Best,
>>> 
>>> Seung Lee Kwon
>>> 
>>> 2023년 5월 3일 (수) 오후 7:30, Matthew Knepley <knepley at gmail.com <mailto:knepley at gmail.com>>님이 작성:
>>>> On Wed, May 3, 2023 at 6:05 AM ­권승리 / 학생 / 항공우주공학과 <ksl7912 at snu.ac.kr <mailto:ksl7912 at snu.ac.kr>> wrote:
>>>>> Dear developers
>>>>> 
>>>>> I'm trying to use parallel computing and I ran the command 'mpirun -np 4 ./app'
>>>>> 
>>>>> In this case, there are two problems.
>>>>> 
>>>>> First, I encountered error message
>>>>> ///
>>>>> [0]PETSC ERROR: [1]PETSC ERROR: --------------------- Error Message --------------------------------------------------------------
>>>>> [1]PETSC ERROR: Invalid argument
>>>>> [1]PETSC ERROR: Comm must be of size 1
>>>>> ///
>>>>> The code on the error position is 
>>>>> MatCreateSeqDense(PETSC_COMM_SELF, nns, ns, NULL, &Kns));
>>>> 
>>>> 1) "Seq" means sequential, that is "not parallel".
>>>> 
>>>> 2) This line should still be fine since PETSC_COMM_SELF is a serial communicator
>>>> 
>>>> 3) You should be checking the error code for each call, maybe using the CHKERRQ() macro
>>>> 
>>>> 4) Please always send the entire error message, not a snippet
>>>> 
>>>>   THanks
>>>> 
>>>>      Matt
>>>>  
>>>>> Could "MatCreateSeqDense" not be used in parallel computing?
>>>>> 
>>>>> Second, the same error message is repeated as many times as the number of cores.
>>>>> if I use command -np 4, then the error message is repeated 4 times.
>>>>> Could you recommend some advice related to this?
>>>>> 
>>>>> Best,
>>>>> Seung Lee Kwon
>>>>> 
>>>>> -- 
>>>>> Seung Lee Kwon, Ph.D.Candidate
>>>>> Aerospace Structures and Materials Laboratory
>>>>> Department of Mechanical and Aerospace Engineering
>>>>> Seoul National University
>>>>> Building 300 Rm 503, Gwanak-ro 1, Gwanak-gu, Seoul, South Korea, 08826
>>>>> E-mail : ksl7912 at snu.ac.kr <mailto:ksl7912 at snu.ac.kr>
>>>>> Office : +82-2-880-7389
>>>>> C. P : +82-10-4695-1062
>>>> 
>>>> 
>>>> -- 
>>>> 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/>
>>> 
>>> 
>>> -- 
>>> Seung Lee Kwon, Ph.D.Candidate
>>> Aerospace Structures and Materials Laboratory
>>> Department of Mechanical and Aerospace Engineering
>>> Seoul National University
>>> Building 300 Rm 503, Gwanak-ro 1, Gwanak-gu, Seoul, South Korea, 08826
>>> E-mail : ksl7912 at snu.ac.kr <mailto:ksl7912 at snu.ac.kr>
>>> Office : +82-2-880-7389
>>> C. P : +82-10-4695-1062
>> 
> 
> 
> -- 
> Seung Lee Kwon, Ph.D.Candidate
> Aerospace Structures and Materials Laboratory
> Department of Mechanical and Aerospace Engineering
> Seoul National University
> Building 300 Rm 503, Gwanak-ro 1, Gwanak-gu, Seoul, South Korea, 08826
> E-mail : ksl7912 at snu.ac.kr <mailto:ksl7912 at snu.ac.kr>
> Office : +82-2-880-7389
> C. P : +82-10-4695-1062

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