dolfin team mailing list archive

[Kent Andre <kent-and@xxxxxxxxx>]

On sø., 2009-08-16 at 23:17 +0200, Anders Logg wrote:
> On Sun, Aug 16, 2009 at 04:36:33PM +0100, Garth N. Wells wrote:
> >
> >
> > Anders Logg wrote:
> > > What is the reason for using int instead of uint in the precomputed
> > > DofMap?
> > >
> >
> > I didn't make it int, but I suspect that it is to leave open the
> > possibility of using negative indexes which some libraries (e.g. PETSc)
> > treat differently during insertion.
> 
> Negative indices will affect all backends. Does Trilinos support it?


The negative indices are not sent to the backend. In the present
(cellwise)  situation this have been easy to avoid, but in the general
case I think one probably need to implement this a separate step where
only the non-negative indices are copied to an additional array. 

Kent   

> 
> > > Also, would it be good to have the same DofMapBuilder::build()
> > > implementation both in parallel and serial. I imagine the algorithm
> > > will specialize to the case of one process. This will be useful to
> > > have once we add the localized iteration over cells on each mesh to
> > > minimize bandwidth.
> >
> > DofMapBuilder::build() does not build the DofMap (name needs to be
> > changed).
> 
> Yes, maybe DofMapRenumbering is better.
> 
> > It renumbers the dofs and is not required when running in serial.
> 
> I think it is. The FFC generated dof map does not do a very good job
> at minimizing bandwidth for vector-valued elements (or even scalar
> P2). I was hoping the same algorithm would work in both serial and
> parallel (less code to maintain).
> 
> --
> Anders
> 
> 
> > I have added a FIXME (might not have pushed it yet) that
> > DofMap::parallel_build needs to be broken into two functions. The first
> > function should determine ownership of dofs when running in parallel,
> > and the second does the re-numbering.
> >
> > Garth
> >
> > >
> >
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