[petsc-users] Generating data on dmplex with varying DOFs

[Matthew Knepley]

On Sun, Jul 17, 2022 at 7:41 AM Prateek Gupta <prateekgupta1709 at gmail.com>
wrote:

> Thanks!
> On a similar note, is it possible to define data on faces of a parallel
> (distributed) dmplex? I have seen the example particular to finite volume
> methods. But the examples I am building are block-spectral where each
> element has a higher order polynomial running (much like spectral element
> methods without the nuisance to separate edge modes and nodal modes).
>

Yes, you can do this. For example,
https://gitlab.com/petsc/petsc/-/blob/main/src/dm/impls/plex/tutorials/ex8.c
shows closures for spectral elements.


> What I am interested in is,
>
> 1. Define face data with multiple DOFs.
>

Yes, faces are mesh points, just like vertices, edges, and cells.


> 2. A quick way of exchanging this face data between processors for
> calculating fluxes.
>

GlobalToLocal will do this.


> I have written all of this by hand already. Just wanted to check and
> compare if dmplex would offer some performance improvement.
>

Possibly. There are some nice optimizations in PetscSF.


> Additionally, petscFV could be extended to petscSD (SD stands for spectral
> difference), where finite volume implementation is the zeroth order special
> case.
>

How is SD different from a spectral element method, with respect to data
layout and communication?

  Thanks,

     Matt


> Thank you.
> Sincerely,
> Prateek Gupta, PhD
>
>
> On Fri, Jul 15, 2022 at 5:43 PM Matthew Knepley <knepley at gmail.com> wrote:
>
>> On Fri, Jul 15, 2022 at 7:08 AM Prateek Gupta <prateekgupta1709 at gmail.com>
>> wrote:
>>
>>> Hi,
>>> Is it possible to generate data using PetscSection with varying degrees
>>> of freedom? I am building a sample example on a mixed grid (with both
>>> hexahedra and tetrahedra) and thinking if it is possible to generate the
>>> face data using PetscSection (or something else) on the resulting. The quad
>>> faces have p*p data points and tri faces have p*(p-1)/2 data points.
>>>
>>
>> Yes, you can set the size to whatever you want using
>>
>>   PetscSectionSetDof()
>>   PetscSectionSetFieldDof()
>>
>> The DMPlexCreateSection() routine is overly simplistic here since I
>> assume all k-cells have the same layout.
>>
>>   Thanks,
>>
>>      Matt
>>
>>
>>> Thank you.
>>> Sincerely,
>>> Prateek Gupta, PhD
>>>
>> --
>> 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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