[Dune] Performace of ISTL

[Christian Engwer]

Dear Patrick,

> > And there is an other question:
> > Is there no easy way, to get a global, consecutive integer id in a 
> > parallel DUNE code? I know, there is the global id, which I can compare 
> > and sort, but if I have such an integer index I can feed my problem to a 
> > parallel Trilinos solver in a very easy way. 
> 
> No there is no consecutive global id, as it is hard to support this
> together with adaptivity.

For a static grid (between the adaptation steps) you can easily
compute global index. You communicate the local size and then you can
compute a global index based on the process id, the sizes of all
preceeding process and the local index.
 
> > An other application for 
> > such an index will be, to write the solution from different processes in 
> > the same hdf5 file.
> 
> Does it really have to be consecutive for this task?
> 
> > I have a look at the global id and I saw, that it consists of 4 
> > integers. Is any functionality to send such a global id object via MPI? 
> > Then can I build my own integer index.
> > 
> 
> I do not know how the global id is implement and it might even be
> different between various grids. 

It is different between various grids. Legacy grid managers usually
use long int for the global id, but this is not sufficient for big
simulations.

Christian