[Dune] Comment to task #120.

[Robert Kloefkorn]

Hi all,

> Secondly it's not that all normals of the reference quad
> point outwards while they should point inwards.  The
> problem is that _some_ point outwards and _some_ inwards.
> Of course I know which do which, and I can write code
> like
> if (subface==1 || subface==3)
>   // reorient face

if that is the problem then I suggest to add a method to the reference
elementes to return 1.0 or -1.0 depending on the normal pointing outward
or inward. By multiplying with this factor, one always get a outward (or
maybe inward) pointing normal for each face. The we have to change
nothing of our exsiting code and we solve this problem too. Also this
factor tell you the orientation of this face and you can take care of it
in your code.
Besides orientation of faces is, what a TwistUtility is good for.
Andreas will comment that piece of code.

> I'm afraid I didn't express myself precisely enough in the
> FlySpray entry.  The problem is not the ordering of the
> vertices of the reference elements as such but the ordering
> of the vertices of subfaces of the reference elements when
> you access them through the subEntity method.
> Of course
> I don't know your code but I'd be surprised if it relied
> a lot on that ordering.

Is has to do with the mapping from the Dune reference elements to the
ALUGrid internal reference elementes. It was really hard to get this
working and I would like to leave it the way it is. Changes a this point
will de-stabilize the whole code again.
Especially face mappings were the most work, when implementing the
entity method in ALUGrid. Here you have to provide a mapping from the
Dune faces of a cube to the ALUGrid faces of a cube.
I really don't want to touch this code again.

Regards

R

-- 

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

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