dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Thu, Aug 14, 2008 at 11:48:14AM +0200, Johan Hoffman wrote:
> > On Wed, Aug 13, 2008 at 2:57 PM, Johan Hoffman <jhoffman@xxxxxxxxxx>
> > wrote:
> >
> >> >
> >> >
> >> > Johan Hoffman wrote:
> >> >>>
> >> >>> Anders Logg wrote:
> >> >>>> On Tue, Jun 17, 2008 at 02:45:41PM +0100, Garth N. Wells wrote:
> >> >>>>> It would be useful to lay out a plan for tackling DofMaps. Getting
> >> >>>>> this
> >> >>>>> right is the key to parallel assembly, assembly optimisations and
> >> >>>>> applying Dirichlet boundary conditions by eliminating Dirichlet
> >> dofs
> >> >>>>> from the global system.
> >> >>>>>
> >> >>>>> I'm happy to take a look, but I'll need some time because I've
> >> lost
> >> >>>>> my
> >> >>>>> overview of DofMaps. If someone else is already on top of it, I'd
> >> be
> >> >>>>> happy to provide feedback.
> >> >>>>>
> >> >>>>> Garth
> >> >>>> I won't have time to look at it until after the summer and I
> >> haven't
> >> >>>> started.
> >> >>>>
> >> >>>> Anyway, I think we should wait until after the next release until
> >> we
> >> >>>> start messing with the dof maps.
> >> >>>>
> >> >>>> Are there any issues we need to sort out before releasing 0.8? I'm
> >> >>>> thinking about a new release some time this or next week.
> >> >>>>
> >> >>>> One is to fix the bug in DirichletBC, but other than that?
> >> >>>>
> >> >>> Now would be a good time for a release so I can start messing with
> >> >>> DofMaps.
> >> >>>
> >> >>> Garth
> >> >>
> >> >> Has anything more been done about the DofMap design? During the
> >> summer
> >> >> Niclas has extended to general elements his adaptive algorithm for
> >> >> distributed parallel computing, so we are now ready to start messing
> >> >> with
> >> >> the DofMaps in order to implement his algorithm in DOLFIN.
> >> >>
> >> >
> >> > It has been given some thought, but no changes have been made in the
> >> > code yet.
> >>
> >> Ok. Any threads on the list to point to where this is discussed?
> >>
> >> If you have something already, I would suggest making it
> >> > publicly available somewhere for feedback before starting work on
> >> DOLFIN.
> >>
> >> It is a refinement and generalization of the thesis work of Niclas
> >> Jansson
> >> which was discussed on the list before the summer. Is is outlined in his
> >> report:
> >>
> >> http://www.nada.kth.se/utbildning/grukth/exjobb/rapportlistor/2008/rapporter08/jansson_niclas_08051.pdf
> >>
> >> My announcement here was to initiate a discussion of the detailed
> >> implementation, and to check if other DOLFIN-people were working on
> >> similar stuff to avoid double/conflicting development.
> >>
> >> /Johan
> >>
> >
> > Very good. We were about to start on this task, so now a good point in
> > time
> > to join forces.
> > As a starting point, it would be nice to agreeing on what data is needed
> > in
> > addition to the partitioned meshes to construct the global dofmap. I.e.
> > which MeshFunctions to construct during the mesh paritioning process. Are
> > you people using the same {T,S,F} input as Anders describes in Algorithm 5
> > in his paper?
> 
> We have discussed this, and it seems that for our adaptive algorithms we
> need some more info. Basically, we have two aims:
> 
> 1. Fully distributed computing (no collection of data on one processor)
> 2. Possibility for dynamic load balancing
> 
> To realize 1-2 we need information on the processor ownership of entities,
> and for resdistributing the mesh we need global vertex numbering. That is,
> we would need something like: {T,S,F,V,O}, where V is global vertex number
> and O is information whether boundary (between processors) vertices are
> own by the processor or if they are ghost nodes.

How do you deal with global edge or face numbers?

My suggestion is to start without a global numbering and then build it
(in parallel).

>  Possibly this is too much information, since for example S,F can be
> computed from V,O, but by storing all info faster algorithms can be
> constructed, so there is a trad-off between speed and memory.
> 
> What do you say?

If you have something that works, just send us a patch so we can try it.

-- 
Anders

Attachment: signature.asc
Description: Digital signature