[petsc-users] Question about DMPlexDistribute & distribute mesh over processes

[Matthew Knepley]

On Sat, May 28, 2022 at 1:35 PM Sami BEN ELHAJ SALAH <
sami.ben-elhaj-salah at ensma.fr> wrote:

> Hi Matthew,
>
> Thank you for your response.
>
> I don't have that. My DM object is not linked to PetscSection yet. I'll
> try that.
> Is there any example that manages this case? (DMPlexDistribute &
> PetscSection) or any guideline will be helpful.
>

Here is an example where we create a section without DS.

  THanks,

    Matt


> Thanks in advance,
>
> Sami,
>
> --
> Dr. Sami BEN ELHAJ SALAH
> Ingénieur de Recherche (CNRS)
> Institut Pprime - ISAE - ENSMA
> Mobile: 06.62.51.26.74
> Email: sami.ben-elhaj-salah at ensma.fr <sami.ben-elhaj-salah at ensma.fr>
> www.samibenelhajsalah.com
> <https://samiben91.github.io/samibenelhajsalah/index.html>
>
>
>
> Le 27 mai 2022 à 20:45, Matthew Knepley <knepley at gmail.com> a écrit :
>
> On Fri, May 27, 2022 at 9:42 AM Sami BEN ELHAJ SALAH <
> sami.ben-elhaj-salah at ensma.fr> wrote:
>
>> Hello Isaac,
>>
>> Thank you for your reply!
>>
>> Let me confirm that when I use DMCreateMatrix() with the orig_dm, I got
>> my jacobian_matrix. Also, I have succeeded to solve my system and my
>> solution was converged* by using one process*.
>> Let me give you some other information about my code. Currently, I am
>> using my own discretization system and not the PetscDS object. Considering
>> the nonlinear solver SNES, I use the following routines (like the basic
>> snes usage):
>> - SNESSetFunction(snes,residual_vector,compute_residual ,(void*)
>> _finite_element_formulation)
>> - SNESSetJacobian(snes, jacobian.matrix(), _jacobian_precond_matrix,
>> compute_jacobian, (void*) _finite_element_formulation)
>> - SNESSolve(snes,NULL,x)
>>
>> Regarding  your last answer, I will try to reformulate my question as
>> follows:
>> Using a distributed dm instead of the original dm (not distributed dm)
>> and my own discretization system (not the PetscDS object),
>>
>
> You do not have to use PetscDS, but the DM does need to a PetscSection in
> order to compute sizes and sparsity patterns. Do you have that?
>
>   Thanks,
>
>      Matt
>
>
>> should I add something specific to get a distributed jacobian_matrix over
>> processes?
>> I precise that I just replaced the orig_dm by a distributed mesh with the
>> routine that I wrote in my first mail. So is it enough ?
>>
>> Thank you and have a good day,
>> Sami,
>>
>>
>> --
>> Dr. Sami BEN ELHAJ SALAH
>> Ingénieur de Recherche (CNRS)
>> Institut Pprime - ISAE - ENSMA
>> Mobile: 06.62.51.26.74
>> Email: sami.ben-elhaj-salah at ensma.fr <sami.ben-elhaj-salah at ensma.fr>
>> www.samibenelhajsalah.com
>> <https://samiben91.github.io/samibenelhajsalah/index.html>
>>
>>
>>
>> Le 25 mai 2022 à 19:41, Toby Isaac <toby.isaac at gmail.com> a écrit :
>>
>> Hi Sami,
>>
>> Just to verify: if you call DMCreateMatrix() on orig_dm, do you get a
>> Jacobian matrix?
>>
>> The DMPlex must be told what kind of discretized fields you want a
>> matrix for and what equations you are discretizing.  This is handled
>> by the PetscDS object.  In snes/tutorials/ex59.c, see the code after
>> DMGetDS() for an example.
>>
>> - Toby
>>
>> On Wed, May 25, 2022 at 1:17 PM Sami BEN ELHAJ SALAH
>> <sami.ben-elhaj-salah at ensma.fr> wrote:
>>
>>
>> Dear PETSc developer team,
>>
>> I m trying to create à jacobian_matrix from distributed DM. I have
>> followed the two examples (snes/tests/ex2.c and ex56.c). So I wrote this
>> routine:
>>
>> PetscDM orig_dm;
>> PetscDM dist_dm = NULL;
>> PetscPartitioner part;
>> DMPlexGetPartitioner(orig_dm, &part);
>> PetscPartitionerSetType(part, PETSCPARTITIONERPARMETIS);
>> DMPlexDistribute(orig_dm, 0, NULL, &dist_dm);
>>
>> PetscErrorCode err = DMCreateMatrix(dist_dm, &jacobian_matrix);
>> PetscInt M, N, m, n;
>> MatGetSize(jacobian_matrix, &M, &N);
>> MatGetLocalSize(jacobian_matrix, &m, &n);
>>
>> Then I run my code with 2 processes and I obtained this result:
>> Size from jacobian_matrix: M=0 m =0 (this result is the same in all
>> processes).
>>
>> I didn't understand if I forgot something in my code to obtain the
>> correct values for the local and global sizes for the jacobean_matrix? (I
>> mean if my code is missing something to obtain a distributed mesh over
>> processes ?)
>>
>> Thank you in advance for any help!
>> Sami,
>>
>>
>> --
>> Dr. Sami BEN ELHAJ SALAH
>> Ingénieur de Recherche (CNRS)
>> Institut Pprime - ISAE - ENSMA
>> Mobile: 06.62.51.26.74
>> Email: sami.ben-elhaj-salah at ensma.fr <sami.ben-elhaj-salah at ensma.fr>
>> www.samibenelhajsalah.com
>>
>>
>>
>>
>>
>
> --
> 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/>
>
>
>

-- 
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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