[Dune] reminder

[Peter Bastian]

Am Donnerstag, den 18.06.2009, 10:25 +0200 schrieb Andreas Dedner:
> Hi,
> during the summer school two questions arose:
> 1) Oliver asked about uniqueness of ids:
>      I have been wondering about the precise semantics of ids.  In
>      particular,  can two entities in the same grid, but with different
>      codimensions, have the same id?
>      - the gridpaper (part I) says they can
>      - The file http://www.dune-project.org/doc/devel/indexidsets.html
>        says they cannot
Ovbviously, that should not be the case.

>      - both the grid howto and the class documentation do not say
>        anything about this
>      - UGGrid allows entities with different codimensions to have the
>        same id.
>      Is this a bug?
> 2) Can ids be reused during the grid modification, i.e., can a new
>     entity have the id of a vanished entity?
> 
> We think that
> 1) ids should be unique through all codimensions
I think the same. Otherwise you would have to code this uniqueness
yourself in order to identify multiple codim entities between
processors.

> 2) ids can be reused during one grid change
If I remember right it is said in the grid paper that IDs cannot be
reused in one grid modification step. If this is done, will you use the
NEW flag to check if the identity is really new?

Peter