[petsc-users] Question on DMPlexCreateFromCellList and DMPlexCreateFromFile

[Matthew Knepley]

On Fri, Feb 16, 2018 at 11:36 AM, Danyang Su <danyang.su at gmail.com> wrote:

> On 18-02-15 05:57 PM, Matthew Knepley wrote:
>
> On Thu, Feb 15, 2018 at 7:40 PM, Danyang Su <danyang.su at gmail.com> wrote:
>
>> Hi Matt,
>>
>> I have a question on DMPlexCreateFromCellList and DMPlexCreateFromFile.
>> When use DMPlexCreateFromFile with Gmsh file input, it works fine and each
>> processor gets its own part. However, when use DMPlexCreateFromCellList,
>> all the processors have the same global mesh. To my understand, I should
>> put the global mesh as input, right?
>
>
> No. Each process should get part of the mesh in CreateFromCellList(), but
> the most common thing to do is to
> feed the whole mesh in on proc 0, and nothing in on the other procs.
>
> Thanks for the explanation. It works now.
>

Great. Also feel free to suggest improvements, examples, or better
documentation.

  Thanks,

     Matt


> Danyang
>
>
>   Thanks,
>
>     Matt
>
>
>> Otherwise, I should use DMPlexCreateFromCellListParallel instead if the
>> input is local mesh.
>>
>> Below is the test code I use, results from method 1 is wrong and that
>> from method 2 is correct. Would you please help to check if I did anything
>> wrong with DMPlexCreateFromCellList input?
>>
>> !test with 4 processor, global num_cells = 8268, global num_nodes = 4250
>>
>> !correct results
>>
>>  check rank            2  istart         2034  iend         3116
>>  check rank            3  istart         2148  iend         3293
>>  check rank            1  istart         2044  iend         3133
>>  check rank            0  istart         2042  iend         3131
>>
>> !wrong results
>>
>>   check rank            0  istart         8268  iend        12518
>>   check rank            1  istart         8268  iend        12518
>>   check rank            2  istart         8268  iend        12518
>>   check rank            3  istart         8268  iend        12518
>>
>>
>>       !c *************    test part    *********************
>>       !c method 1: create DMPlex from cell list, same duplicated global
>> meshes over all processors
>>       !c the input parameters num_cells, num_nodes, dmplex_cells,
>> dmplex_verts are all global parameters (global mesh data)
>>       call DMPlexCreateFromCellList(Petsc_Comm_World,ndim,num_cells,   &
>> num_nodes,num_nodes_per_cell,      &
>> Petsc_True,dmplex_cells,ndim,      &
>> dmplex_verts,dmda_flow%da,ierr)
>>       CHKERRQ(ierr)
>>
>>
>>       !c method 2: create DMPlex from Gmsh file, for test purpose, this
>> works fine, each processor gets its own part
>>       call DMPlexCreateFromFile(Petsc_Comm_World,                      &
>> prefix(:l_prfx)//'.msh',0,             &
>>                                 dmda_flow%da,ierr)
>>       CHKERRQ(ierr)
>>
>>       !c *************end of test part*********************
>>
>>
>>       distributedMesh = PETSC_NULL_OBJECT
>>
>>       !c distribute mesh over processes
>>       call DMPlexDistribute(dmda_flow%da,0,PETSC_NULL_OBJECT,          &
>>                             distributedMesh,ierr)
>>       CHKERRQ(ierr)
>>
>>       !c destroy original global mesh after distribution
>>       if (distributedMesh /= PETSC_NULL_OBJECT) then
>>         call DMDestroy(dmda_flow%da,ierr)
>>         CHKERRQ(ierr)
>>         !c set the global mesh as distributed mesh
>>         dmda_flow%da = distributedMesh
>>       end if
>>
>>       !c get coordinates
>>       call DMGetCoordinatesLocal(dmda_flow%da,gc,ierr)
>>       CHKERRQ(ierr)
>>
>>       call DMGetCoordinateDM(dmda_flow%da,cda,ierr)
>>       CHKERRQ(ierr)
>>
>>       call DMGetDefaultSection(cda,cs,ierr)
>>       CHKERRQ(ierr)
>>
>>       call PetscSectionGetChart(cs,istart,iend,ierr)
>>       CHKERRQ(ierr)
>>
>> #ifdef DEBUG
>>         if(info_debug > 0) then
>>           write(*,*) "check rank ",rank," istart ",istart," iend ",iend
>>         end if
>> #endif
>>
>>
>> Thanks and regards,
>>
>> Danyang
>>
>>
>
>
> --
> 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.caam.rice.edu/%7Emk51/>
>
>
>


-- 
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.caam.rice.edu/~mk51/>
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