[petsc-users] PETSC FVM view gradient

[Matthew Knepley]

On Tue, Jul 21, 2020 at 6:12 AM Thibault Bridel-Bertomeu <
thibault.bridelbertomeu at gmail.com> wrote:

> Dear all,
>
> This request stems from the "How to add a source term for PETSCFV ?"
> thread.
> Basically, I would like to output in a VTK file all the components of the
> gradient computed using the following piece of code (given sol is a global
> representation of the solution over the whole mesh described by the manager
> dm with a unique field fvm).
>
>   ierr = PetscFVSetComputeGradients(fvm,PETSC_TRUE);CHKERRQ(ierr);  ierr = DMConvert(dm, DMPLEX, &plex);CHKERRQ(ierr);  ierr = DMPlexGetDataFVM(plex, fvm, &cellGeom, &faceGeom, &gradDM);CHKERRQ(ierr);  ierr = DMCreateLocalVector(plex,&locX);CHKERRQ(ierr);  ierr = DMPlexInsertBoundaryValues(plex, PETSC_TRUE, locX, 0.0, faceGeom, cellGeom, NULL);CHKERRQ(ierr);  ierr = DMGlobalToLocalBegin(plex, sol, INSERT_VALUES, locX);CHKERRQ(ierr);  ierr = DMGlobalToLocalEnd  (plex, sol, INSERT_VALUES, locX);CHKERRQ(ierr);  ierr = DMCreateGlobalVector(gradDM, &grad);CHKERRQ(ierr);  ierr = DMPlexReconstructGradientsFVM(plex, locX, grad);CHKERRQ(ierr);  ierr = DMCreateLocalVector(gradDM, &locGrad);CHKERRQ(ierr);  ierr = DMGlobalToLocalBegin(gradDM, grad, INSERT_VALUES, locGrad);CHKERRQ(ierr);  ierr = DMGlobalToLocalEnd(gradDM, grad, INSERT_VALUES, locGrad);CHKERRQ(ierr);  ierr = VecDestroy(&grad);CHKERRQ(ierr);
>
>   ierr = PetscViewerCreate(PetscObjectComm((PetscObject)gradDM), &viewer);CHKERRQ(ierr);
>
>   ierr = PetscSNPrintf(filename,sizeof filename,"%s-%03D-gradient.vtu",user->outputBasename,stepnum);CHKERRQ(ierr);
>
>   ierr = PetscViewerSetType(viewer, PETSCVIEWERVTK);CHKERRQ(ierr);  ierr = PetscViewerFileSetName(viewer, filename);CHKERRQ(ierr);
>
>   ierr = VecView(locGrad,viewer);CHKERRQ(ierr);
>
>
> I am having troubles with a few things I think but I cannot figure out how
> to put it together in the right order ...
> (i) I am not sure whether VecView should be called with a local or a
> global vector
>

Does not matter, so you can just use the global vector.


> (ii) I can see from the error log that gradDM does not have fields and
> thus when it goes through dmplexvtu.c it crashes and cannot write the file.
> I tried to add the fvm as a field, but it does not work either, it crashes
> on a memory corruption.
>

Can you show the error? The above looks correct to me.

  Thanks,

    Matt


> Could somebody please advise ?
>
> Thank you very much in advance,
>
> Thibault Bridel-Bertomeu
> —
> Eng, MSc, PhD
> Research Engineer
> CEA/CESTA
> 33114 LE BARP
> Tel.: (+33)557046924
> Mob.: (+33)611025322
> Mail: thibault.bridelbertomeu at gmail.com
>
>
>>>
>>>

-- 
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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