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

[Sami BEN ELHAJ SALAH]

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.
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
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 <mailto: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 <mailto: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 <mailto: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 <mailto: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 <mailto:sami.ben-elhaj-salah at ensma.fr>
>>> www.samibenelhajsalah.com <http://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/>

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