[petsc-users] Question on DMPlexCreateFromCellList and DMPlexCreateFromFile

[Danyang Su]

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 
> <mailto: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.

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/>

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