dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Tue, Feb 19, 2008 at 09:18:54AM +0100, Johan Hoffman wrote:
> > On Mon, Feb 18, 2008 at 04:35:54PM +0100, Johan Hoffman wrote:
> >> > This is good juncture at which re-focus on important goals for a
> >> hopefully not too distant next release. Three priorities that I see are:
> >> >
> >> > - New build system.
> >> >
> >> > - Improved support for parallel assembly and solve. The class Function
> >> will probably need the most work. Good goals would be to get Poisson and
> >> elasticity demos running in parallel.
> >>
> >> I thought the Poisson problem was running, and showing good parallel
> >> scaling? Or maybe that was a test outside the dolfin-dev demos?
> >
> > The demo is in src/demo/fem/assembly/.
> 
> Ok, so the matrix assembly is working and is implemented as a demo, but
> solve is missing.

Two things are missing: solve and handling forms with coefficients in
parallel (the Vector in DiscreteFunction holding the dofs should be
parallel).

Garth has done parallel solve (with PETSc) in src/sandbox/passembly/main.cpp
so it shouldn't be much work to get the solve part going.

> >> We (Nicklas) have now a preliminary distributed parallel implementation
> >> running for Poisson and a Unicorn flow solver. The structure is still
> >> quite messy and the partitioning is based on Metis, but we expect it to
> >> be
> >> integrated with DOLFIN in the coming months, hopefully before the
> >> summer.
> >
> > Could this be done in small pieces? I'm a little worried about seeing
> > big changesets that add things to the mesh classes.
> 
> Yes, we need to figure out how this should be done to best fit with the
> existing mesh classes. When we have cleaned up the code we will take that
> discussion here at the dolfin mailing list so that we can agree on a
> solution.

Excellent.

> >> When the structure is more clear we can discuss on the mailing list how
> >> to
> >> best incorporate this into DOLFIN. Apart from the structure of the
> >> implementation we are also focusing on distributed local mesh
> >> refinement.
> >
> > Great.
> >
> > What is the difference from what we have now? Is it the same but with
> > a distributed mesh (so each processor just sees the local part, not
> > the whole mesh)? Or is it something different?
> 
> I think the main issues are to handle refinement over
> partition-boundaries, and efficient re-partitioning after refinement (for
> load-balancing).

ok, we haven't considered this at all.

> > I think what we have now can be fairly easily extended to a
> > distributed mesh without any (significant) changes to the mesh
> > classes. The key point is to build the DofMap in parallel. Take a look
> > here, in particular Section 6 and Algorithm 5:
> >
> >   http://simula.no/research/scientific/publications/Simula.SC.75
> >
> 
> Seems I need a username/password for this.

Sorry, try here:

  http://home.simula.no/~logg/tmp/

-- 
Anders


> /Johan
> 
> >> > - Testing of QuadratureFunction and adding corresponding demos.
> >> >
> >> > Another point is to add Trilinos as a supported linear algebra back
> >> end.
> >> How does this tie up with closer links to PyCC?
> >> >
> >> > Garth
> >>
> >> - Something else that I think is important is to include geometry in
> >> DOLFIN. We were to start such a project before Christmas, but we lost
> >> the
> >> msc student that was supposed to work on this. I would expect that we
> >> restart this later this spring. Basically we need to import CAD-geometry
> >> (or other geometry descriptions), create an internal DOLFIN format
> >> (typically based on NURBS or similar) with a Geometry-class. Typical
> >> functionality needed is then to project a point onto the surface
> >> geometry.
> >
> > That would be nice.
> >
> >
> >
> >> /Johan
> >>
> >>
> >> > _______________________________________________
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> >> >
> >>
> >>
> >>
> >>
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> 
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