[Dune] New subentity numbering

[Andreas Dedner]

>> Is it really impossible to rewrite the generic geometry stuff in a way
>> that it preserves the old numbering, at least for simplices and cubes?
Tell us how - although we will not do it. Your few days work was
about a few months work on our side!
And we never had 4D simplicies before. There was never any information
what so ever on how subentities of subentities are numbered - so talk
about complete documentation!

>> The cubes were generated generically before, so this should still be
>> possible.  And I don't see any reason why it should not be possible
>> for the simplices. 
We have asked (more than once) for a documentation of the generic cubes
- with no results - so we made are own, which are consistent with the
way all the other geometries are built, so it is in fact rather easy to
understand

>> Not a single word about the differences, nor about which is the old
>> and which is the new method, and that it is dangerous to mix the use
>> of old and new methods.  Furthermore, 95 % of the code in
>> grid/genericgeometry is without any documentation (not even
>> comments!).  Even parts of the code that are meant to be directly used
>> by DUNE users are lacking any documentation (for example
>> GenericReferenceElements).  And finally, the transition page itself is
>> all but complete (for example, no word about the orientation changes
>> of subentities).
A comment on where documentation is missing would be more helpful than a
remark that it is missing. As soon as we got concrete suggestions of
where documentation should be added, it never took long for us to write
it.


>>
>> To be clear about this:  I really like that we have generic geometries
>> now -- they facilitate new grid implementations and reduce code
>> duplication.  But I can't see any advantages of the new numbering, and
>> I would like to have documentation for the generic geometry code.
>>
We want work on anything new with respect to generic geometries. So if
the general feeling is to go back to the old things, we can put that to
a vote or else somebody should say that he is willing to spend a few
months on writing new generic geometries and I wish him the best.

Andreas