[petsc-dev] Best Way to Assign Cell Number to VTK Plot in DMPlex

[Matthew Knepley]

On Thu, Oct 3, 2019 at 11:42 AM Matthew Knepley <knepley at gmail.com> wrote:

> On Tue, Oct 1, 2019 at 11:57 AM Faibussowitsch, Jacob via petsc-dev <
> petsc-dev at mcs.anl.gov> wrote:
>
>> Hello All,
>>
>> I am plotting an output value from a vecview, and want to show in a
>> separate plot which cells correspond to which values in the vec. I plan to
>> do this by making a field on the cells whose value is the global number of
>> that cell. I have 2 issues with this:
>>
>> 1. How do I guarantee that the ordering of the Vec I made corresponds to
>> the DMPlex cell ordering such that Vec(0) corresponds to Cells(0) etc. (I
>> make the Vec separately from the DM since using DMCreateLocalVector makes a
>> vector on the vertices)
>>
>> 2. I am trying to use DMPlexVTKWriteAll to make my output, so I am adding
>> my field to the DMPlexVTK using PetscViewerVTKAddField, but I can’t seem to
>> get PetscViewerVTKWriteFunction to work properly, and the man pages don’t
>> link to an example. Here is my code for this section:
>>
>> PetscErrorCode        (*PetscViewerVTKWriteFunction) (PetscObject,
>> PetscViewer);
>>
>> ierr = PetscViewerCreate(comm=PETSC_COMM_WORLD, &vtkviewer);CHKERRQ(ierr);
>> ierr = PetscViewerVTKOpen(comm=PETSC_COMM_WORLD, "mesh.vtk",
>> FILE_MODE_WRITE, &vtkviewer);CHKERRQ(ierr);
>> ierr = PetscViewerSetUp(vtkviewer);CHKERRQ(ierr);
>>
>> PetscViewerVTKWriteFunction = (CellNum vtkviewer);
>>
>> ierr = PetscViewerVTKAddField(vtkviewer, (PetscObject) dm,
>> PetscViewerVTKWriteFunction, PETSC_VTK_CELL_FIELD, PETSC_TRUE,
>> CellNum);CHKERRQ(ierr);
>> ierr = DMPlexVTKWriteAll((PetscObject) dm, vtkviewer);CHKERRQ(ierr);
>>
>> Any help would be greatly appreciated!
>>
>
> I think what you want is to make a Section over cells with 1 dof, fill it
> with the cell number (from a global numbering), and then view that Vec.
>

Here is me making a similar field containing the rank instead of the cell
number:


https://www.mcs.anl.gov/petsc/petsc-master/docs/manualpages/DMPLEX/DMPlexCreateRankField.html

Note that Paraview already knows the cell number and can display it

  Thanks,

     Matt


>    Matt
>
>
>> Best,
>>
>> Jacob
>>
>>
>
> --
> 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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