dolfin team mailing list archive

[Niclas Jansson <njansson@xxxxxx>]

Ola Skavhaug wrote:
> On Wed, Aug 13, 2008 at 2:57 PM, Johan Hoffman <jhoffman@xxxxxxxxxx 
> <mailto: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?
>
>
> Ola

No, we use a set of MeshFunctions marking ghosted/shared vertices.
However, the algorithm is almost the same.

Input: Distributed mesh T

1) extract interior boundary I of T  (boundary between processors).

2) iterate over I and decide which processor should renumber which 
shared dof.

3) compute offset_i for each processor i.

4) renumber all dofs on processor i starting from offset_i (local + 
(assigned) shared).

5) exchange assigned numbers for shared dofs.

Niclas

>  
>
>
>     >
>     > Garth
>     >
>     >
>     >> I see Anders report referenced in the code, where the mapping
>     scheme
>     >> described is fairly close to what Niclas has implemented,
>     although there
>     >> are some differences. We will sit down today to sum up what we
>     think
>     >> needs
>     >> to be done, and then we can discuss this on the mailing list.
>     >>
>     >> /Johan
>     >>
>     >>
>     >>
>     >>
>     >>
>     >>
>     >>
>     >>
>     >
>     >
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>
> --
> Ola Skavhaug