dolfin team mailing list archive

["Johan Hoffman" <jhoffman@xxxxxxxxxx>]

> 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?

I believe this is rebuilt from global vertex numbers.

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

I am not sure how from only local info you can construct information on
which boundary vertices are owned by which processes?

>>  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.

Niclas can send you his code.

/Johan

> --
> Anders
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