[petsc-users] Numbering convention

[Matthew Knepley]

On Sat, Aug 14, 2021 at 12:19 AM Miguel Angel Tapia <miguel.td19 at outlook.com>
wrote:

> Hello. First of all thanks for the answers to the previous questions. They
> were really useful to me.
>
> Now I am facing a new problem. The code in which I want to implement
> DMPlex has a specific order in which it orders the elements that make up
> other elements for meshes of tetrahedra. But when I get the elements that
> make up some point of the DMPlex DAG they don't match what I need. So I
> would like to know what is the numbering convention for meshes of
> tetrahedra that is used in DMPlex?
>

We need to be a little more precise, so I can understand what you need.

We usually begin with a cell associated to a set of vertices. Our reference
tetrahedron is composed of the vertices, numbered 0 to 3:

  (-1, -1, -1) -- (-1, 1, -1) -- (1, -1, -1) -- (-1, -1, 1)

The triangular faces, numbers 0 to 3, are composed of the vertices

  {0, 1, 2}, {0, 3, 1}, {0, 2, 3}, {2, 1, 3}

Notice that they all have outward normal.

  Thanks,

     Matt

-- 
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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