dolfin team mailing list archive

["Garth N. Wells" <g.n.wells@xxxxxxxxxx>]

Martin Sandve Alnæs wrote:
> On 12/7/06, Garth N. Wells <g.n.wells@xxxxxxxxxx> wrote:
> > Martin Sandve Alnæs wrote:
>
> Yes, but that's a separate issue.
>
> We're probably just talking past each other here.
>
> After looking at your code again, I think the misunderstanding is in this:
> (I don't know PetSC, so I might be wrong here)
>
> You call VecCreateMPI(..., n_local, n_global, &vec), which probably
> distributes the global vector entries in contiguous chunks to
> processes. If you didn't renumber, I now see your "problem".
>
> I've used an Epetra_Map(..., array_of_local_entries, n_local) which
> distributes the global vector entries with a completely general
> local-to-global mapping. 

I see now how Epetra works. Epetra_Map creates a mapping between global 
and local indices. Do you create this, or does Epetra create it for you 
on the fly as you insert terms? I'm building this map manually.

When you have things running with Epetra and we have things up and 
running with PETSc, it would be nice to compare the performance of the 
two. Looks like Epetra has some nice functionality.

Garth

But the local Epetra_Vector will store its
> local entries in a contiguous array, so there is an implicit
> renumbering here. But it is not a renumbering of the global dofs, it
> is a separate renumbering or mapping between local and global vector
> indices. With this approach, there is no connection between the
> numbering of the global dofs and the communication amount.
>
> martin