[Dune] The subentity numbering again...

[Oliver Sander]

I support this proposal.  It seems like a reasonable compromise
to me.

I would have liked to keep the old hypercube numberings.
However I know that Sven put some thought into how to do that,
and that he would have proposed it if it was feasable.

--
Oliver

Sven Marnach schrieb:
> Hi all,
>
> last week I had a long phone call with Martin.  Among other things, we
> discussed again the possibilities of changing the subentity numbering.
>
> After discussion among the people in Heidelberg, we suggest the
> follwoing changes to the current generic numbering:
>
>  1. The old 2D simplex numbering is recovered by special-casing.  This
>     special case is used as a basis for recursively building higher
>     dimension simplices.  These will be numbered generically according
>     to the rules in 2.
>
>  2. When recursively building the higher dimension simplex E° from a
>     simplex E, the subentities are numbered in the following way:
>
>       * First, all subentities of E° which are not part of E get the
>         numbers of the subentities of E which they are based on.
>
>       * Then the subentities of E° which are contained in E are
>         numbered consecutively in the same ordering as they were
>         numbered before.
>
>     This will recover opposite-vertex numbering for the faces of a
>     simplex of any dimension, except for the 1D simplex (but in the
>     case of 1D simplces, opposite-vertex numbering would mean that a
>     vertex should get a different number when the vertex is considered
>     as a face).
>
>  3. The cubes will retain their current generic numbering (i.e. the
>     one introduced by Martin and Andreas).
>
>  4. The numberings of prisms and pyramids change according to the
>     rules in 2.
>
> This numbering has the following advantages:
>
>  1. The numbering in 2D will be completely the same as before.  Many
>     people only have 2D codes, which will essentially work unchanged
>     (of course, method calls have to be changed to the new method
>     names).
>
>  2. In 3D, the old numbering of vertices and faces is preserved for
>     cubes and simplices.  Only the edge numbering of simplices and
>     cubes will change.  This will not affect as many people as
>     renumbering faces.
>
>  3. Simplices will retain opposite-vertex numbering.  This is what
>     most people expect because it is already used in school.  It is
>     also more intuitive for P1 finite elements.  (People _really_
>     expect this.  We were already asked why on earth we adopted a
>     numbering which does not have opposite-vertex numbering.)
>
>  4. The faces of 2D simplices will be numbered anticlockwise, which
>     again is what most people expect.
>
> Martin thinks that these changes would be possible whith some minor
> changes to the current code.
>
> What is the opinion of the DUNE developers on this topic?  Who is in
> favor of adopting this proposal?
>
> Regards from Heidelberg,
>     Sven
>
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>   


-- 
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* Oliver Sander                ** email: sander at mi.fu-berlin.de        *
* Freie Universität Berlin     ** phone: + 49 (30) 838 75348           *
* Institut für Mathematik      ** URL  : page.mi.fu-berlin.de/~sander  *
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