[petsc-users] MatView to file

[Alfredo Jaramillo]

Hello Mark,
But why should this depend on the number of processes?
thanks
Alfredo

On Fri, Aug 12, 2022 at 1:42 PM Mark Adams <mfadams at lbl.gov> wrote:

> With 4 million elements you are nowhere near the 32 but integer limit of
> 2B or 32Gb of memory.
>
> See the https://petsc.org/main/docs/manualpages/Mat/MatView
> You should go to binary format when doing large matrices.
>
> Mark
>
> On Fri, Aug 12, 2022 at 1:00 PM Alfredo Jaramillo <
> ajaramillopalma at gmail.com> wrote:
>
>> Hello Mark,
>> Thank you, I added the lines that you sent.
>> This only happens when running the code with more than 1 process. With
>> only 1 MPI process the matrix is printed out.
>> With 2 processes or more I observed the program begins to allocate RAM
>> until it exceeds the computer capacity (32GB) so I wasn't able to get the
>> stack trace.
>>
>> However, I was able to reproduce the problem by compiling
>> src/ksp/ksp/tutorials/ex54.c.html
>> <https://petsc.org/release/src/ksp/ksp/tutorials/ex54.c.html> (modifying
>> line 144) and running it with
>>
>> mpirun -np 2 ex54 -ne 1000
>>
>> This gives a sparse matrix of order ~1 million. When running ex54 with
>> only one MPI process I don't observe this excessive allocation and the
>> matrix is printed out.
>>
>> Thanks,
>> Alfredo
>>
>>
>>
>> On Fri, Aug 12, 2022 at 10:02 AM Mark Adams <mfadams at lbl.gov> wrote:
>>
>>> You also want:
>>>
>>>     PetscCall(PetscViewerPopFormat(viewer));
>>>     PetscCall(PetscViewerDestroy(&viewer));
>>>
>>> This should not be a problem.
>>> If this is a segv and you configure it with   '--with-debugging=1', you
>>> should get a stack trace, which would help immensely.
>>> Or run in a debugger to get a stack trace.
>>>
>>> Thanks,
>>> Mark
>>>
>>>
>>>
>>> On Fri, Aug 12, 2022 at 11:26 AM Alfredo Jaramillo <
>>> ajaramillopalma at gmail.com> wrote:
>>>
>>>> Dear developers,
>>>>
>>>> I'm writing a sparse matrix into a file by doing
>>>>
>>>>     if (dump_mat) {
>>>>         PetscViewer viewer;
>>>>         PetscViewerASCIIOpen(PETSC_COMM_WORLD,"mat-par-aux.m",&viewer);
>>>>         PetscViewerPushFormat(viewer, PETSC_VIEWER_ASCII_MATLAB);
>>>>         MatView(A,viewer);
>>>>     }
>>>>
>>>> This works perfectly for small cases.
>>>> The program crashes for a case where the matrix A is of order 1 million
>>>> but with only 4 million non-zero elements.
>>>>
>>>> Maybe at some point petsc is full-sizing A?
>>>>
>>>> Thank you,
>>>> Alfredo
>>>>
>>>
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