[petsc-users] local/global DMPlex Vec output

[Matteo Semplice]

Dear Matt,

     I guess you're right: thresholding by rank==0 and rank==1 in 
paraview reveals that it is indeed the overlap cells that are appear 
twice in the output.

The attached file is not exactly minimal but hopefully short enough. If 
I run it in serial, all is ok, but with

     mpirun -np 2 ./saveDemo

it creates a 10x10 grid, but I get "output.vtu" with a total of 120 
cells. However the pointSF of the DMPlex seems correct.

Thanks

     Matteo

Il 21/10/24 19:15, Matthew Knepley ha scritto:
> On Mon, Oct 21, 2024 at 12:22 PM Matteo Semplice via petsc-users 
> <petsc-users at mcs.anl.gov> wrote:
>
>     Dear petsc-users,
>
>         I am having issues with output of parallel data attached to a
>     DMPlex (or maybe more fundamental ones about DMPlex...).
>
>     So I currently
>
>      1. create a DMPlex (DMPlexCreateGmshFromFile or DMPlexCreateBoxMesh)
>      2. partition it
>      3. and create a section for my data layout with
>         DMPlexCreateSection(ctx.dmMesh, NULL, numComp, numDof, numBC,
>         NULL, NULL, NULL, NULL, &sUavg)
>      4. DMSetLocalSection(ctx.dmMesh, sUavg)
>      5. create solLoc and solGlob vectors with DMCreateGlobalVector
>         and DMCreateLocalVector
>      6. solve ....
>      7. VecView(ctx.solGlob, vtkViewer) on a .vtu file
>
>     but when I load data in ParaView I get more cells than expected
>     and it is as if the cells in the halo are put twice in output. (I
>     could create a MWE if the above is not clear)
>
> I think we need an MWE here, because from the explanation above, it 
> should work.
>
> However, I can try to guess the problem. When you partition the mesh, 
> I am guessing that you have cells in the overlap. These cells
> must be in the point SF in order for the global section to give them a 
> unique owner. Perhaps something has gone wrong here.
>
>   Thanks,
>
>      Matt
>
>     I guess that the culprit is point (4), but if I replace it with
>     DMSetGlobalSection then I cannot create the local vector at point (5).
>
>     How should I handle this properly? In my code I need to create
>     both local and global vectors, to perform at least GlobalToLocal
>     and to save the global data.
>
>     (On a side note, I tried also HDF5 but then it complains about the
>     DM not having a DS...; really, any working solution that allows
>     data to be explored with Paraview is fine)
>
>     Thanks for any advice!
>
>     Matteo Semplice
>
>
>
> -- 
> 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
>
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-- 
---
Professore Associato in Analisi Numerica
Dipartimento di Scienza e Alta Tecnologia
Università degli Studi dell'Insubria
Via Valleggio, 11 - Como
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