[petsc-users] basis/basisDer/Jac in FE

[Mark Adams]

Area of a unit triangle is (1x1)/2 I would guess.

On Thu, Oct 27, 2022 at 11:32 AM Yann Jobic <yann.jobic at univ-amu.fr> wrote:

> Hello,
>
> I'm trying to understand how to use the lowlevel Petsc Finit Element
> Framework. I've got few questions about it.
>
> 1) I'm checking the determinant of the Jacobian transformation from real
> space to the parametric one. The source code is in :
>
> https://petsc.org/main/src/dm/impls/plex/plexgeometry.c.html#DMPlexComputeTriangleGeometry_Internal
> I don't quite understand the 0.5 factor in front of it.
> Geometrically, it should be the ratio of the area/volume of the reel
> element over the referenced one. It's not the case here no ?
> It seems that, for other elements, this factor still applies.
> What this factor represent ?
>
> 2) I only checked triangle elements here. The ordering of the test
> functions and its derivatives is different it seems, with also the 0.5
> factor. Am i mistaken ?
>
> I could not find any informations about it in the user-doc. Maybe it's
> written somewhere else ?
>
> Many Thanks,
>
> Best regards,
>
> Yann
>
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