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

[Matthew Knepley]

On Sun, Jul 17, 2022 at 10:51 AM Prateek Gupta <prateekgupta1709 at gmail.com>
wrote:

> SD is a collocation method. Imagine a finite volume method, but instead of
> a single point (cell and face centers), data is distributed over a grid
> within the cell and the intersection of the grid with each of the cell's
> faces. So unlike FV, the communication is for a DIM-1 dimensional grid on
> the faces. I'll see if the SEM closures help me.
>

That sounds like the same layout and communication as high order DG.

  Thanks,

     Matt


>
> Thank you.
> Sincerely,
> Prateek Gupta, PhD
>
>
> On Sun, Jul 17, 2022 at 7:59 PM Matthew Knepley <knepley at gmail.com> wrote:
>
>> 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/>
>>
>

-- 
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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