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

[Matthew Knepley]

On Fri, Oct 4, 2019 at 3:09 PM Faibussowitsch, Jacob <
jfaibussowitsch at anl.gov> wrote:

> Note that Paraview already knows the cell number and can display it
>
> Now that would have been useful to know months ago.
>
> Here is me making a similar field containing the rank instead of the cell
> number:
>
> Yes I ended up cannibalizing that function and this worked well enough.
> One thing I noticed however is that it the global vector this creates is of
> the size of number of cells, but when I create a global vector it is the
> size of num vertices.
>

If you are requesting a Vec from a Plex, then the discretization in its DS
determines its size. You need to

  make a clone (DMClone) and set a P0 discretization

This is what I do there.

   Matt


> I omitted the PETSc__rank_ options prefix part when creating the default
> fe, is that responsible for setting the vec size here?
>
> Best,
>
> Jacob
>
> On Oct 4, 2019, at 9:42 AM, Matthew Knepley <knepley at gmail.com> wrote:
>
> 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/>
>
>
>

-- 
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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