What version of PETSc are you using? The output looks a little funny.
Would you be willing to send your code to petsc-ma...@mcs.anl.gov
<mailto:petsc-ma...@mcs.anl.gov> so I can debug it quickly?
> On May 29, 2023, at 9:54 PM, Waltz Jan <jl2862237...@gmail.com> wrote:
>
> Thank you for your reply and help. I followed your advice to try it out, but
> found that the results were not quite right. It may be due to my
> misunderstanding. Could you please help me? The specific information is as
> follows:
>
> Codes:
> /* Solve J Y = F, where J is Jacobian matrix */
> ierr = SNESComputeJacobian(snes, X, snes->jacobian, snes->jacobian_pre);
> CHKERRQ(ierr);
>
> PetscViewer viewer;
> /* View the matrix in a text file */
> ierr = PetscViewerASCIIOpen(PETSC_COMM_WORLD,
> "/share/userfile/jianglei/Muti-layers-well-working/petsc/jacobianmatrix.m",
> &viewer);CHKERRQ(ierr);
> ierr = PetscViewerPushFormat(viewer,
> PETSC_VIEWER_ASCII_MATLAB);CHKERRQ(ierr); /* Optional: use MATLAB format */
> ierr = MatView(snes->jacobian, viewer);CHKERRQ(ierr);
> ierr = PetscViewerDestroy(&viewer);CHKERRQ(ierr);
>
> MatAssemblyBegin(snes->jacobian,MAT_FINAL_ASSEMBLY);
> MatAssemblyEnd(snes->jacobian,MAT_FINAL_ASSEMBLY);
> PetscInt rstart, rend;
> MatGetOwnershipRange(snes->jacobian, &rstart, &rend);
> PetscInt row=1000, col=1000;
> PetscScalar v;
>
> if (row>=rstart && row<rend)
> {
> MatGetValues(snes->jacobian, 1, &row, 1, &col, &v);
> PetscPrintf(PETSC_COMM_WORLD, "rstart: %d, rend: %d, row: %d, col: %d,
> v: %e\n", rstart, rend, row, col, PetscRealPart(v));
> }
>
> Results:
> <image.png>
> <image.png>
> <image.png>
> ====================== Step: 1, time: 0. days====================
> 0 SNES Function norm 1.772062116708e-01
> rstart: 0, rend: 4000, row: 1000, col: 1000, v: 7.443232e-06
>
> That's all. Could you help me?
>
>
> On Tue, May 30, 2023 at 1:00 AM <petsc-users-requ...@mcs.anl.gov
> <mailto:petsc-users-requ...@mcs.anl.gov>> wrote:
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>> Today's Topics:
>>
>> 1. MatGetValues() can't return the correct values (Waltz Jan)
>> 2. Re: MatGetValues() can't return the correct values (Barry Smith)
>>
>>
>> ----------------------------------------------------------------------
>>
>> Message: 1
>> Date: Mon, 29 May 2023 16:49:40 +0800
>> From: Waltz Jan <jl2862237...@gmail.com <mailto:jl2862237...@gmail.com>>
>> To: petsc-users@mcs.anl.gov <mailto:petsc-users@mcs.anl.gov>
>> Subject: [petsc-users] MatGetValues() can't return the correct values
>> Message-ID:
>> <CAEj=jGKvgY5ys=4_=YoEZrE5Xu4Pj6FVxSq8XgUH=N=qf_c...@mail.gmail.com
>> <mailto:qf_c...@mail.gmail.com>>
>> Content-Type: text/plain; charset="utf-8"
>>
>> /* Solve J Y = F, where J is Jacobian matrix */
>> ierr = SNESComputeJacobian(snes, X, snes->jacobian, snes->jacobian_pre);
>> CHKERRQ(ierr);
>>
>> PetscInt rstart, rend;
>> MatGetOwnershipRange(snes->jacobian, &rstart, &rend);
>> PetscInt row=1000, col=1000;
>> PetscScalar v;
>> if (row>=rstart && row<rend)
>> {
>> MatGetValues(snes->jacobian, 1, &row, 1, &col, &v);
>> PetscPrintf(PETSC_COMM_WORLD, "rstart: %d, rend: %d, row: %d, col: %d,
>> v: %e\n", rstart, rend, row, col, v);
>> }
>>
>> It was supposed to return the value of the matrix at row 1001 and column
>> 1001, but it returned the value at row 2001 and column 2001 instead. There
>> is a two-fold relationship between these coordinates, and I'm not sure if
>> it's related to the fact that I set the number of processes to 2.
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>> ------------------------------
>>
>> Message: 2
>> Date: Mon, 29 May 2023 11:01:32 -0400
>> From: Barry Smith <bsm...@petsc.dev <mailto:bsm...@petsc.dev>>
>> To: Waltz Jan <jl2862237...@gmail.com <mailto:jl2862237...@gmail.com>>
>> Cc: petsc-users@mcs.anl.gov <mailto:petsc-users@mcs.anl.gov>
>> Subject: Re: [petsc-users] MatGetValues() can't return the correct
>> values
>> Message-ID: <99a3d1b8-6ca1-41c3-8b19-e68f90a67...@petsc.dev
>> <mailto:99a3d1b8-6ca1-41c3-8b19-e68f90a67...@petsc.dev>>
>> Content-Type: text/plain; charset="us-ascii"
>>
>>
>> Perhaps run a very small problem with 2 ranks and use MatView() to see
>> the matrix before getting the values. Maybe use the debugger
>> (-start_in_debugger) and step through the code as it gets values. I would
>> say there is very little chance it is getting the "wrong values" and is more
>> likely due to a misunderstanding of the matrix usage.
>>
>> Barry
>>
>>
>>
>>
>> > On May 29, 2023, at 4:49 AM, Waltz Jan <jl2862237...@gmail.com
>> > <mailto:jl2862237...@gmail.com>> wrote:
>> >
>> > /* Solve J Y = F, where J is Jacobian matrix */
>> > ierr = SNESComputeJacobian(snes, X, snes->jacobian, snes->jacobian_pre);
>> > CHKERRQ(ierr);
>> >
>> > PetscInt rstart, rend;
>> > MatGetOwnershipRange(snes->jacobian, &rstart, &rend);
>> > PetscInt row=1000, col=1000;
>> > PetscScalar v;
>> > if (row>=rstart && row<rend)
>> > {
>> > MatGetValues(snes->jacobian, 1, &row, 1, &col, &v);
>> > PetscPrintf(PETSC_COMM_WORLD, "rstart: %d, rend: %d, row: %d, col: %d,
>> > v: %e\n", rstart, rend, row, col, v);
>> > }
>> >
>> > It was supposed to return the value of the matrix at row 1001 and column
>> > 1001, but it returned the value at row 2001 and column 2001 instead. There
>> > is a two-fold relationship between these coordinates, and I'm not sure if
>> > it's related to the fact that I set the number of processes to 2.
>>
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>>
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