[Dune] Re: Notification from Dune

[Robert Kloefkorn]

Hi Christian, hi others,

> We discussed this issue in Stuttgart and we decided, that this issue
> must be solved before 1.0 in the one ore other way. Oliver complains,
> that the faces in the reference quad are oriented with some normal
> vectors pointing outwards and some pointing inwards.

The problem described in the task in not nice, I agree.

> We agree, that it would be nice to have all normalvectors pointing
> inwards (like in the reference triangle). The current orientation
> arises from the fact, that the reference cubes are constructed via
> tensor product.

Peter decided to have the reference cubes that way to provide
n-dimensions reference cubes. That is a good reason.

To keep this feature it would be a better way to change the simplex
reference elements. It really makes no difference whether the normals
point outward or inward, you just have to know which direction.

> If it is managable, we should do this change before 1.0, because
> changing the semantics of the reference cube after 1.0 would be a
> really bad idea; the api would stay the same and no user whould be
> warned to change his code. Really strange and hard to find errors
> would be the result.

This change is gonna be hard at any time. It will effect almost all
parts of the ALUGrid implementation, the complete dune-fem package,
everything that has to do with quadrature rules, visualization (at least
grape). This will change be worse than the GeometryType change.
I'm, so to speak, "completely against" this change.

> If it is to hard to implement we should just close the bug as "won't
> fix".

This problem arrises from the definition, that the geometry type line is
always interpreted as a cube which is (with our current implementation
of the reference elements) obviously not the case. If one can fix this
problem, the described problem in the task will disappear.
An easy fix will be, that a line, belonging to a triangle, is a simplex
too, a line belonging to a quadrilateral is a cube.

Regards,

R

-- 

  Robert Klöfkorn           <robertk at mathematik.uni-freiburg.de>

  Mathematisches Institut              Tel: +49 (0) 761 203 5631
  Abt. für Angewandte Mathematik       Fax: +49 (0) 761 203 5632
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