[Dune] Accessing cells from faces

[Dragan Vidovic]

Hi all

I use a LeafGridView::template Codim<1>::Iterator to iterate all faces
in the grid. For each face I need to refer to the neighboring cells
(codim 0) and get their centroids. I guess it's only possible to refer
from a cell to a face and not the other way around because this would
require some extra storage, but before I start hacking it I'd like to
ask if someone knows something about this.

Thanks

Dragan