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

[Sami BEN ELHAJ SALAH]

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), 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
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
>> www.samibenelhajsalah.com
>> 
>> 
>> 

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