[Dune] local vertex indices

[Carsten Gräser]

Hi Lars,

Am 27.01.2014 18:35, schrieb Lars Lubkoll:
> I am using Dune 2.2.1 with UGGrid and have a question regarding the
> connection between local vertex indices of an intersection and one of
> its neighbouring tetrahedra.
> Is there a way to get the vertex indices wrt. the tetrahedron from
> indices wrt. the intersection?
> For me the problem seems to be how to get a codim<1>-entity of a cell.
> Then I would use the subEntity-method of GenericReferenceElement to map
> the indices. But it seems as if codim<1>-entities do not exist.
I'm afraid, that there's no way besides comparing coordinates
for two reasons:

* First of all intersection vertices are not necessarily element
  vertices. This is for example the case for nonconforming grid.

* Even for the codim<1>-subentity this does not work, since its
  vertex numbering does not correspond to the subEntity method
  of the reference element, because the latter does only enumerate
  the subentity vertices. The reason for this is that a global ordering
  and orientation of subentities that guarantees this consistency
  property with respect to all adjacent elements does not exist
  in general. However you can at least compare global indices
  instead of coordinates using the subIndex method.

While comparing coordinates sounds dangerous its not problematic
here, because you only have to consider global coordinates in the
element.

Best,
Carsten