[petsc-users] Wrapper function to factorize a matrix

[Matthew Knepley]

On Mon, Oct 21, 2019 at 9:30 PM Zhang, Hong via petsc-users <
petsc-users at mcs.anl.gov> wrote:

> Shash,
> You may do it without using pc. See petsc/src/mat/examples/tests/ex125.c
>

Does this example let you invert the matrix and just apply to get the solve?

  Thanks,

    Matt


> Hong
>
> On Mon, Oct 21, 2019 at 4:43 PM Shashwat Sharma via petsc-users <
> petsc-users at mcs.anl.gov> wrote:
>
>> Hello,
>>
>> For some small matrices, I'd like to use Petsc to perform direct LU
>> factorization on a sequential dense or AIJ matrix, and then use the
>> factored matrix later on via MatSolve. This occurs multiple times in my
>> code, and each factored matrix is in turn used multiple times.
>>
>> I tried to wrap this factorization process in a function, which should
>> return the factored matrix, as follows:
>>
>> void MatFactorize_Petsc(Mat &mat, Mat &mat_factored)
>> {
>> PC pc;
>> PCCreate(MPI_COMM_SELF, &pc);
>> PCSetOperators(pc, mat, mat);
>> PCSetType(pc, PCLU);
>>
>> PCFactorSetMatSolverType(pc, MATSOLVERPETSC); // Or SuperLU
>> PCFactorSetUpMatSolverType(pc);
>>
>> PCFactorGetMatrix(pc, &mat_factored);
>> PCSetUp(pc);
>> // PCDestroy(&pc);
>> return;
>> }
>>
>> The command PCDestroy causes a segmentation fault, which I think happens
>> because retrieving the factored matrix does not increase the reference
>> count. Looking at the Petsc source, it basically returns a pointer to
>> pc->data. So if I want to use mat_factored outside the function, I cannot
>> destroy the PC object, which leads to memory leaks (as per Valgrind) even
>> if I later call MatDestroy(&mat_factored).
>>
>> I tried using a temp matrix to get the factors, and then doing
>> MatDuplicate(temp, MAT_COPY_VALUES, &mat_factored), but MatDuplicate is not
>> allowed on factored matrices; same for MatConvert.
>>
>> Is there a way I can achieve the desired behaviour, where mat_factored is
>> not "linked" to the pc or ksp object, keeping in mind that I'd like to be
>> able to choose between SuperLU, Petsc and SuperLU_dist solvers?
>>
>> Thanks,
>> Shash
>>
>>

-- 
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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