[petsc-users] DMPlex Reordering

[Nicholas Arnold-Medabalimi]

Hi Matt

Could you clarify what DMPlexOrient is doing as far as the metric for
compatibility for orientation?

Sincerely
Nicholas

On Mon, Jul 25, 2022 at 11:54 AM Matthew Knepley <knepley at gmail.com> wrote:

> On Mon, Jul 25, 2022 at 10:11 AM Nicholas Arnold-Medabalimi <
> narnoldm at umich.edu> wrote:
>
>> Hi Petsc users,
>>
>> I have been working on how to read in meshes into a DMPlex object. The
>> process of building the cones has been relatively straightforward. The mesh
>> files in question have sets of faces that I use to derive the cell vertex
>> cones. The method is basically identical to that used in
>> DMPlexCreateFluent. After I setup the DMPlex cones and call Symmetrize and
>> Stratify, I then load in all the coordinates corresponding to the
>> vertices and then use DMInterpolate to generate the intermediate edges
>>
>> The issue that I am running into is that because I am deriving the
>> cell-vertex relationship from independent sets of face-vertex
>> relationships, I can end up with cells that have improper mesh ordering.
>>
>> For example a cell with the coordinates:
>> point 0: 0.000000 0.000000
>> point 1: 0.000000 2.500000
>> point 2: 0.100000 0.000000
>> point 3: 0.100000 2.500000
>>
>> As you can see instead of going around the perimeter of the cell the path
>> from 1 to 2 instead bisects the cell.
>>
>> I can manually reorder these after I read in the coordinates by manually
>> checking right-handedness but I was wondering if there is an easier way to
>> reorder the cones? If there isn't once I do reorder the cones manually is
>> there anything I need to do as far as station keeping on the DM?
>>
>
> The function DMPlexOrient() reorders the cones so that all cells have
> compatible orientation. However, it will not catch this because it is
> an illegal ordering for a quad. This order is called
> a DM_POLYTOPE_SEG_PRISM_TENSOR in Plex because it is the tensor product of
> two segments (so that opposite sides have the same orientation). If all
> your cells are this way, you can just mark them as tensor segments
> and you are done. If only some turn out this way, then we have to write
> some code to recognize them, or flip them when you create the cones.
>
>   Thanks,
>
>     Matt
>
>
>> I apologize if I missed any resources on this.
>>
>> Thanks
>> Nicholas
>>
>> --
>> Nicholas Arnold-Medabalimi
>>
>> Ph.D. Candidate
>> Computational Aeroscience Lab
>> University of Michigan
>>
>
>
> --
> 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/>
>


-- 
Nicholas Arnold-Medabalimi

Ph.D. Candidate
Computational Aeroscience Lab
University of Michigan
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