[Dune] VertexIterator vs. CornerIterator in VTKWriter

[Christian Engwer]

Hi Jö,

please remeber that postings on this list should be in english
languange.

> In VTKWriter sowohl eine CornerIterator als auch einen VertexIterator, wobei
> der CornerIterator ein Subset vom VertexIterator (für datamode=nonconforming)
> zu sein scheint.  Hat das einen tieferen Sinn?

Within the VTKWriter it is necessary to loop over all vertices and to
loop over all global positions of vertices in the reference
element. The corneriterator always performs the "non-conforming"
iteration, i.e. loops over all corners of all elements. The
vertexiterator loops over all vertices inteh grid, this behavior
changes depending on the conforming/non-conforming view.

In the case of conforming data you need both types, in the case of
non-conforming data indeed they give the same set of points.

Christian