[petsc-users] DMPlexCreateFromDAG for P2 elements

[Asitav Mishra]

Matt,

Please excuse me for not having stated it clearly. Of course, ultimately
residuals/Jacobians are what I'd need to evaluate using higher-order nodes.
I just meant my first concern is to create a mesh graph structure that can
be appropriately partitioned (and hopefully re-distributed) among multiple
processors without losing the higher order topological information of the
geometry, such as those in curved (higher-order) elements.

Thanks,
Asitav

On Wed, Oct 9, 2019 at 12:25 AM Matthew Knepley <knepley at gmail.com> wrote:

> On Tue, Oct 8, 2019 at 4:45 PM Asitav Mishra via petsc-users <
> petsc-users at mcs.anl.gov> wrote:
>
>> Stefano,
>>
>> Thanks a lot for your prompt response. I have a higher-order mesh, so
>> will need to create my own PetscSection to add the local coordinates looks
>> like.
>> At this point, FEM residuals and Jacobian computations are not as
>> important. But, could you direct me to any examples in creating
>> PetscSection for such elements?
>>
>
> Asitav,
>
> What do you want to do with higher oder coordinate embeddings, if not
> calculate residuals and Jacobians?
> Are you absolutely certain that is what you need, since this is not
> normally called P2.
>
>   Thanks,
>
>      Matt
>
>
>> Thanks,
>> Asitav
>>
>> On Tue, Oct 8, 2019 at 3:18 PM Stefano Zampini <stefano.zampini at gmail.com>
>> wrote:
>>
>>> DMPlex abstracts the mesh topology. PetscSection defines the dofs
>>> associated to the mesh entities.
>>> Why do you need P2 elements? For the discrete solution or because you
>>> have a high order mesh?
>>>
>>> If it is only for the solution, you should create a linear mesh
>>> (cell-vertex only), interpolate the mesh, and then use
>>> PetscFECreateDefault (
>>> https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/FE/PetscFECreateDefault.htm
>>> )
>>> +
>>> DMAddField (
>>> https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/DM/DMAddField.html
>>> )
>>> +
>>> DMCreateDS (
>>> https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/DM/DMCreateDS.html
>>> )
>>>
>>> Instead, if you have a high-order mesh, you should create a linear mesh,
>>> and then manipulate yourself the PetscSection defining the local
>>> coordinates.
>>> However, I’m not sure how complete is the support for high-order meshes
>>> when it comes to compute FEM residuals and assemble Jacobians
>>>
>>>
>>> On Oct 8, 2019, at 9:54 PM, Asitav Mishra via petsc-users <
>>> petsc-users at mcs.anl.gov> wrote:
>>>
>>> Hi,
>>>
>>> Does Petsc support DMPlexCreateFromDAG for 2nd order (P2) elements, or
>>> any orders higher than one (P1) for that matter? I know it is possible to
>>> create DMPlex mesh from GMSH files with P2 elements, but not sure how the
>>> 'cone/support' structures are built. One approach is to ignore the higher
>>> order nodes in an element to create the 'cones', but is there a way to
>>> preserve the P2 element information in the 'cones'?
>>>
>>> For example: how would the depth=1 cone structure look like for a mesh
>>> with two P2 triangles sharing a face?
>>>             2
>>>           / | \
>>>         /   |   \
>>>      6     |     8
>>>     /       |       \
>>>   /         |         \
>>> 0   0    5    1    3
>>>   \         |         /
>>>     \       |       /
>>>      4     |     7
>>>         \   |   /
>>>           \ | /
>>>            1
>>>
>>> Higher order nodes: [4, 5, 6, 7, 8]. Can we construct cones with
>>> cells-to-nodes (depth = 1)?:
>>>
>>> numPoints = [9, 2];                                             // 9
>>> nodes instead of just 4?
>>> coneSizes = [6, 6,    0, 0, 0, 0, 0, 0, 0, 0, 0];
>>> cones        = [0, 1, 2, 4, 5, 6,    2, 1, 3, 5, 7, 8];
>>> etc.
>>>
>>> Any help would be greatly appreciated.
>>>
>>> Thanks,
>>> Asitav
>>>
>>> --
>>> Asitav Mishra, PhD
>>> Research Engineer II, NIA
>>>
>>>
>>>
>>
>> --
>> Asitav Mishra, PhD
>> Research Engineer II, NIA
>>
>
>
> --
> 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/>
>


-- 
Asitav Mishra, PhD
Research Engineer II, NIA
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