dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Thu, Feb 03, 2011 at 09:03:58PM +0100, Niclas Jansson wrote:
> Anders Logg <logg@xxxxxxxxx> writes:
>
> > On Tue, Feb 01, 2011 at 11:57:28AM -0000, Anders Logg wrote:
> >> Question #143645 on DOLFIN changed:
> >> https://answers.launchpad.net/dolfin/+question/143645
> >>
> >> Anders Logg proposed the following answer:
> >> On Tue, Feb 01, 2011 at 11:50:37AM -0000, Garth Wells wrote:
> >> > Question #143645 on DOLFIN changed:
> >> > https://answers.launchpad.net/dolfin/+question/143645
> >> >
> >> >     Status: Open => Answered
> >> >
> >> > Garth Wells proposed the following answer:
> >> > I don't think so.
> >>
> >> I think it should be possible, at least "in principle". I'll comment
> >> more later. I'm in a meeting now.
> >
> > Sorry for my late reply.
> >
> > What you can do is to get the "overlap":
> >
> > std::map<uint, std::vector<uint> >* overlap = mesh.data().vector_mapping("overlap");
> >
> > This gives you a mapping for each shared vertex to its neighboring
> > processes (the processes it's shared with).
> >
> > You can check if a vertex is shared by
> >
> >   overlap->find(i) != overlap->end()
> >
> > There is no functionality for checking edges, cells etc. Such
> > operations must be expressed in terms of their vertices.
> >
> > It would be easy to add some shortcuts like
> >
> >   bool Vertex::is_ shared() const;
> >
> > and even
> >
> >   bool MeshEntity::is_shared() const;
> >
> > etc if that helps. They could just look at the overlap.
> >
> > If that is costly, we could store another MeshFunction that holds the
> > appropriate data (or add as part of ParallelData).
> >
> >
>
> Perfect! That should be enough to get me started porting some code.

Great!

> How about owners of mesh entities? If I remember correctly mesh entities
> were not owned by a specific rank. If one could determine if a vertex
> is owned, ghosted or shared, it would make life much simpler when
> implementing various parallel mesh algorithms.

Isn't the rule that when a vertex is shared, it's owned by the lowest
rank process?

I don't know how we handle ghosted entities (or if we even have
ghosted entities). We have ghosted dofs stored in Vectors (handled by
PETSc/Epetra) but I'm not sure how it's handled. Garth knows a great
deal more about that.

--
Anders