[petsc-users] petsc-users Digest, Vol 173, Issue 131

Barry Smith bsmith at petsc.dev
Mon May 29 22:06:01 CDT 2023 

  What version of PETSc are you using? The output looks a little funny.

  Would you be willing to send your code to petsc-maint at mcs.anl.gov <mailto:petsc-maint at mcs.anl.gov> so I can debug it quickly?


> On May 29, 2023, at 9:54 PM, Waltz Jan <jl2862237661 at 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-request at mcs.anl.gov <mailto:petsc-users-request at 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 <jl2862237661 at gmail.com <mailto:jl2862237661 at gmail.com>>
>> To: petsc-users at mcs.anl.gov <mailto:petsc-users at mcs.anl.gov>
>> Subject: [petsc-users] MatGetValues() can't return the correct values
>> Message-ID:
>>         <CAEj=jGKvgY5ys=4_=YoEZrE5Xu4Pj6FVxSq8XgUH=N=QF_C-vA at mail.gmail.com <mailto:QF_C-vA at 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 <bsmith at petsc.dev <mailto:bsmith at petsc.dev>>
>> To: Waltz Jan <jl2862237661 at gmail.com <mailto:jl2862237661 at gmail.com>>
>> Cc: petsc-users at mcs.anl.gov <mailto:petsc-users at mcs.anl.gov>
>> Subject: Re: [petsc-users] MatGetValues() can't return the correct
>>         values
>> Message-ID: <99A3D1B8-6CA1-41C3-8B19-E68F90A67102 at petsc.dev <mailto:99A3D1B8-6CA1-41C3-8B19-E68F90A67102 at 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 <jl2862237661 at gmail.com <mailto:jl2862237661 at 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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>> End of petsc-users Digest, Vol 173, Issue 131
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