[petsc-users] Parallel DMPlex

erdemguer erdemguer at proton.me
Wed Oct 11 03:42:14 CDT 2023 

Hi again,
Here is my code:
#include <petsc.h>
static char help[] = "dmplex";

int main(int argc, char **argv)
{
PetscCall(PetscInitialize(&argc, &argv, NULL, help));
DM dm, dm_dist;
PetscSection section;
PetscInt cStart, cEndInterior, cEnd, rank;
PetscInt nc[3] = {3, 3, 3};
PetscReal upper[3] = {1, 1, 1};

PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD, &rank));

DMPlexCreateBoxMesh(PETSC_COMM_WORLD, 3, PETSC_FALSE, nc, NULL, upper, NULL, PETSC_TRUE, &dm);
DMViewFromOptions(dm, NULL, "-dm1_view");
PetscCall(DMSetFromOptions(dm));
DMViewFromOptions(dm, NULL, "-dm2_view");

PetscCall(DMPlexGetDepthStratum(dm, 3, &cStart, &cEnd));
DMPlexComputeCellTypes(dm);
PetscCall(DMPlexGetCellTypeStratum(dm, DM_POLYTOPE_INTERIOR_GHOST, &cEndInterior, NULL));
PetscPrintf(PETSC_COMM_SELF, "Before Distribution Rank: %d, cStart: %d, cEndInterior: %d, cEnd: %d\n", rank, cStart,
cEndInterior, cEnd);

PetscInt nField = 1, nDof = 3, field = 0;
PetscCall(PetscSectionCreate(PETSC_COMM_WORLD, &section));
PetscSectionSetNumFields(section, nField);
PetscCall(PetscSectionSetChart(section, cStart, cEnd));
for (PetscInt p = cStart; p < cEnd; p++)
{
PetscCall(PetscSectionSetFieldDof(section, p, field, nDof));
PetscCall(PetscSectionSetDof(section, p, nDof));
}

PetscCall(PetscSectionSetUp(section));

DMSetLocalSection(dm, section);
DMViewFromOptions(dm, NULL, "-dm3_view");

DMSetAdjacency(dm, field, PETSC_TRUE, PETSC_TRUE);
DMViewFromOptions(dm, NULL, "-dm4_view");
PetscCall(DMPlexDistribute(dm, 1, NULL, &dm_dist));
if (dm_dist)
{
DMDestroy(&dm);
dm = dm_dist;
}
DMViewFromOptions(dm, NULL, "-dm5_view");
PetscCall(DMPlexGetDepthStratum(dm, 3, &cStart, &cEnd));
DMPlexComputeCellTypes(dm);
PetscCall(DMPlexGetCellTypeStratum(dm, DM_POLYTOPE_FV_GHOST, &cEndInterior, NULL));
PetscPrintf(PETSC_COMM_SELF, "After Distribution Rank: %d, cStart: %d, cEndInterior: %d, cEnd: %d\n", rank, cStart,
cEndInterior, cEnd);

DMDestroy(&dm);
PetscCall(PetscFinalize());}

This codes output is currently (on 2 processors) is:
Before Distribution Rank: 1, cStart: 0, cEndInterior: -1, cEnd: 14
Before Distribution Rank: 0, cStart: 0, cEndInterior: -1, cEnd: 13
After Distribution Rank: 0, cStart: 0, cEndInterior: -1, cEnd: 27After Distribution Rank: 1, cStart: 0, cEndInterior: -1, cEnd: 24

DMView outputs:
dm1_view (after creation):
DM Object: 2 MPI processes
type: plex
DM_0x84000004_0 in 3 dimensions:
Number of 0-cells per rank: 64 0
Number of 1-cells per rank: 144 0
Number of 2-cells per rank: 108 0
Number of 3-cells per rank: 27 0
Labels:
marker: 1 strata with value/size (1 (218))
Face Sets: 6 strata with value/size (6 (9), 5 (9), 3 (9), 4 (9), 1 (9), 2 (9))
depth: 4 strata with value/size (0 (64), 1 (144), 2 (108), 3 (27)) celltype: 4 strata with value/size (7 (27), 0 (64), 4 (108), 1 (144))

dm2_view (after setfromoptions):
DM Object: 2 MPI processes
type: plex
DM_0x84000004_0 in 3 dimensions:
Number of 0-cells per rank: 40 46
Number of 1-cells per rank: 83 95
Number of 2-cells per rank: 57 64
Number of 3-cells per rank: 13 14
Labels:
depth: 4 strata with value/size (0 (40), 1 (83), 2 (57), 3 (13))
marker: 1 strata with value/size (1 (109))
Face Sets: 5 strata with value/size (1 (6), 2 (1), 3 (7), 5 (5), 6 (4)) celltype: 4 strata with value/size (0 (40), 1 (83), 4 (57), 7 (13))

dm3_view (after setting local section):
DM Object: 2 MPI processes
type: plex
DM_0x84000004_0 in 3 dimensions:
Number of 0-cells per rank: 40 46
Number of 1-cells per rank: 83 95
Number of 2-cells per rank: 57 64
Number of 3-cells per rank: 13 14
Labels:
depth: 4 strata with value/size (0 (40), 1 (83), 2 (57), 3 (13))
marker: 1 strata with value/size (1 (109))
Face Sets: 5 strata with value/size (1 (6), 2 (1), 3 (7), 5 (5), 6 (4))
celltype: 4 strata with value/size (0 (40), 1 (83), 4 (57), 7 (13))
Field Field_0: adjacency FEM

dm4_view (after setting adjacency):
DM Object: 2 MPI processes
type: plex
DM_0x84000004_0 in 3 dimensions:
Number of 0-cells per rank: 40 46
Number of 1-cells per rank: 83 95
Number of 2-cells per rank: 57 64
Number of 3-cells per rank: 13 14
Labels:
depth: 4 strata with value/size (0 (40), 1 (83), 2 (57), 3 (13))
marker: 1 strata with value/size (1 (109))
Face Sets: 5 strata with value/size (1 (6), 2 (1), 3 (7), 5 (5), 6 (4))
celltype: 4 strata with value/size (0 (40), 1 (83), 4 (57), 7 (13))
Field Field_0: adjacency FVM++

dm5_view (after distribution):
DM Object: Parallel Mesh 2 MPI processes
type: plex
Parallel Mesh in 3 dimensions:
Number of 0-cells per rank: 64 60
Number of 1-cells per rank: 144 133
Number of 2-cells per rank: 108 98
Number of 3-cells per rank: 27 24
Labels:
depth: 4 strata with value/size (0 (64), 1 (144), 2 (108), 3 (27))
marker: 1 strata with value/size (1 (218))
Face Sets: 6 strata with value/size (1 (9), 2 (9), 3 (9), 4 (9), 5 (9), 6 (9))
celltype: 4 strata with value/size (0 (64), 1 (144), 4 (108), 7 (27))
Field Field_0: adjacency FVM++

Thanks,
Guer.

Sent with [Proton Mail](https://proton.me/) secure email.

------- Original Message -------
On Wednesday, October 11th, 2023 at 3:33 AM, Matthew Knepley <knepley at gmail.com> wrote:

> On Tue, Oct 10, 2023 at 7:01 PM erdemguer <erdemguer at proton.me> wrote:
>
>> Hi,
>> Sorry for my late response. I tried with your suggestions and I think I made a progress. But I still got issues. Let me explain my latest mesh routine:
>>
>> - DMPlexCreateBoxMesh
>>
>> - DMSetFromOptions
>> - PetscSectionCreate
>> - PetscSectionSetNumFields
>> - PetscSectionSetFieldDof
>>
>> - PetscSectionSetDof
>>
>> - PetscSectionSetUp
>> - DMSetLocalSection
>> - DMSetAdjacency
>> - DMPlexDistribute
>>
>> It's still not working but it's promising, if I call DMPlexGetDepthStratum for cells, I can see that after distribution processors have more cells.
>
> Please send the output of DMPlexView() for each incarnation of the mesh. What I do is put
>
> DMViewFromOptions(dm, NULL, "-dm1_view")
>
> with a different string after each call.
>
>> But I couldn't figure out how to decide where the ghost/processor boundary cells start.
>
> Please send the actual code because the above is not specific enough. For example, you will not have
> "ghost cells" unless you partition with overlap. This is because by default cells are the partitioned quantity,
> so each process gets a unique set.
>
> Thanks,
>
> Matt
>
>> In older mails I saw there is a function DMPlexGetHybridBounds but I think that function is deprecated. I tried to use, DMPlexGetCellTypeStratumas in ts/tutorials/ex11_sa.c but I'm getting -1 as cEndInterior before and after distribution. I tried it for DM_POLYTOPE_FV_GHOST, DM_POLYTOPE_INTERIOR_GHOST polytope types. I also tried calling DMPlexComputeCellTypes before DMPlexGetCellTypeStratum but nothing changed. I think I can calculate the ghost cell indices using cStart/cEnd before & after distribution but I think there is a better way I'm currently missing.
>>
>> Thanks again,
>> Guer.
>>
>> ------- Original Message -------
>> On Thursday, September 28th, 2023 at 10:42 PM, Matthew Knepley <knepley at gmail.com> wrote:
>>
>>> On Thu, Sep 28, 2023 at 3:38 PM erdemguer via petsc-users <petsc-users at mcs.anl.gov> wrote:
>>>
>>>> Hi,
>>>>
>>>> I am currently using DMPlex in my code. It runs serially at the moment, but I'm interested in adding parallel options. Here is my workflow:
>>>>
>>>> Create a DMPlex mesh from GMSH.
>>>> Reorder it with DMPlexPermute.
>>>> Create necessary pre-processing arrays related to the mesh/problem.
>>>> Create field(s) with multi-dofs.
>>>> Create residual vectors.
>>>> Define a function to calculate the residual for each cell and, use SNES.
>>>> As you can see, I'm not using FV or FE structures (most examples do). Now, I'm trying to implement this in parallel using a similar approach. However, I'm struggling to understand how to create corresponding vectors and how to obtain index sets for each processor. Is there a tutorial or paper that covers this topic?
>>>
>>> The intention was that there is enough information in the manual to do this.
>>>
>>> Using PetscFE/PetscFV is not required. However, I strongly encourage you to use PetscSection. Without this, it would be incredibly hard to do what you want. Once the DM has a Section, it can do things like automatically create vectors and matrices for you. It can redistribute them, subset them, etc. The Section describes how dofs are assigned to pieces of the mesh (mesh points). This is in the manual, and there are a few examples that do it by hand.
>>>
>>> So I suggest changing your code to use PetscSection, and then letting us know if things still do not work.
>>>
>>> Thanks,
>>>
>>> Matt
>>>
>>>> Thank you.
>>>> Guer.
>>>>
>>>> Sent with [Proton Mail](https://proton.me/) secure email.
>>>
>>> --
>>>
>>> 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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