[dune-pdelab] dune-pdelab | Feature: Divergence and curl as DGF (#15)

[Christian Engwer]

> I do care, but I cannot give an opinion since nobody cares to explain the
> original issue to me.  And I did ask [1].  What is wrong with the existing
> curl DiscreteGridfunctions?
> 
> [1] http://conan2.iwr.uni-heidelberg.de/git/pdelab/dune-pdelab/merge_requests/15#note_1068

I asked this as well and I'm curious which features are lacking in the
old curl implementation and why it can't be achieved by a simplex
fix/patch.

If the only reason is some "not-invented-here", I'm against merging
the new functions.

> And I also don't understand the point about unnecessary deprecations.  When
> the revolution (i.e. dune-function) comes we will probably deprecate _all_ old
> discrete gridfunctions, whether curl or div or just plain old regular ones.
> Until then we use the existing ones, and where those are not enough we can
> continue to create special ones in the style of the existing ones and
> alongside the existing ones (not an option above).  We will have to deprecate
> them, yes, but they will very likely be deprecated along with all the other
> old ones, so I don't see any additional confusion there.

If we introduce new features we encourage people to use it and in some
sense we promise the people that these features will be around for a
while. I consider it unfortunate if we introduce something and
rmeove/deprecate it in the next release. Thus I'd like to put it into
the experimental namespace, in order to signal that we don't promise
anything concerning this feature.

Christian