On 07/03/2021 16:54, Matthew Knepley wrote:
On Sun, Mar 7, 2021 at 8:52 AM Nicolas Barral
<[email protected]
<mailto:[email protected]>> wrote:
Matt,
Thanks for your answer.
However, DMPlexComputeCellGeometryFVM does not compute what I need
(normals of height 1 entities). I can't find any function doing
that, is
there one ?
The normal[] in DMPlexComputeCellGeometryFVM() is exactly what you want.
What does not look right to you?
So it turns out it's not what I want because I need non-normalized
normals. It doesn't seem like I can easily retrieve the norm, can I?
If not, I'll fallback to computing them by hand for now. Is the
following assumption safe or do I have to use DMPlexGetOrientedFace?
> if I call P0P1P2P3 a tet and note x the cross product,
> P3P2xP3P1 is the outward normal to face P1P2P3
> P0P2xP0P3 " P0P2P3
> P3P1xP3P0 " P0P1P3
> P0P1xP0P2 " P0P1P2
Thanks
--
Nicolas
Thanks,
Matt
So far I've been doing it by hand, and after a lot of experimenting the
past weeks, it seems that if I call P0P1P2P3 a tetrahedron and note x
the cross product,
P3P2xP3P1 is the outward normal to face P1P2P3
P0P2xP0P3 " P0P2P3
P3P1xP3P0 " P0P1P3
P0P1xP0P2 " P0P1P2
Have I been lucky but can't expect it to be true ?
(Alternatively, there is a link between the normals and the element
Jacobian, but I don't know the formula and can find them)
Thanks,
--
Nicolas
On 08/02/2021 15:19, Matthew Knepley wrote:
> On Mon, Feb 8, 2021 at 6:01 AM Nicolas Barral
> <[email protected]
<mailto:[email protected]>
> <mailto:[email protected]
<mailto:[email protected]>>> wrote:
>
> Hi all,
>
> Can I make any assumption on the orientation of triangular
facets in a
> tetrahedral plex ? I need the inward facet normals. Do I need
to use
> DMPlexGetOrientedFace or can I rely on either the tet vertices
> ordering,
> or the faces ordering ? Could DMPlexGetRawFaces_Internal be
enough ?
>
>
> You can do it by hand, but you have to account for the face
orientation
> relative to the cell. That is what
> DMPlexGetOrientedFace() does. I think it would be easier to use the
> function below.
>
> Alternatively, is there a function that computes the normals
- without
> bringing out the big guns ?
>
>
> This will compute the normals
>
>
https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/DMPLEX/DMPlexComputeCellGeometryFVM.html
> Should not be too heavy weight.
>
> THanks,
>
> Matt
>
> Thanks
>
> --
> Nicolas
>
>
>
> --
> 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/>
