[petsc-users] Matrix assembly in SNES problem

[Mark Adams]

On Wed, Jul 22, 2020 at 8:05 AM Adolfo Rodriguez <adantra at gmail.com> wrote:

> I am trying to replace the non-linear solver in a flow simulation problem
> where the matrix sparsity can change during the iterations. I tried
> successfully to create the matrix within the FormJacobian function but I
> have a memory leak which I don't know how to fix.
>
> My FormJacobian function is something like this:
>
> .. FormJacobian( ..){
>      matrixconstruction(); // returns csr matrix in c++ regular vectors
>      MatSeqAIJSetPreallocationCSR ...;
>      //loop over the entries and
>      MatSetValues;
>      MatAssemblyBegin();
>      MatAssemblyEnd();
>      return 0;
> }
>
> This approach works for small problems but, when dealing with large ones I
> observe a memory leak.
>

How are you detecting a memory leak? It's odd that you would not see it on
a small problem. You can run with -malloc_debug to get a listing of PETSc
memory that was not freed.


> I am pretty sure that It is related to the fact that I am creating new
> matrices every time FormJacobian is called but I don't know how to destroy
> it between iterations.
>

You don't create the matrix in FormJacobian, do you?
Do your changes (eg, AMR) before or after the time step (you can do this
with a TSSetPostStep and TSSetPreStep), then destroy the old matrix and
vectors.


>
> Any suggestions?
>
> Regards,
>
> Adolfo
>
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