On 07/03/2021 22:30, Matthew Knepley wrote:
On Sun, Mar 7, 2021 at 4:13 PM Nicolas Barral
<[email protected]
<mailto:[email protected]>> wrote:
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]>
> <mailto:[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?
You just want area-weighted normals I think, which means that you just
multiply by the area,
which comes back in the same function.
Ah by the area times 2, of course, my bad.
Do you order height-1 elements in a certain way ? I need to access the
facet (resp. edge) opposite to a vertex in a tet (resp. triangle).
Thanks
--
Nicolas
Thanks,
Matt
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]>>
> > <mailto:[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/>
--
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/>
