dolfin team mailing list archive

["Garth N. Wells" <g.n.wells@xxxxxxxxxx>]

Anders Logg wrote:
> On Wed, Dec 06, 2006 at 11:39:44PM +0100, Garth N. Wells wrote:
> > Anders Logg wrote:
> > > Do you mean "DofMap associated with mesh and finite element"?
> > Yep.
> >
> > > I'm ok with that. We could have a DiscreteFunction with two members:
> > >
> > >     Vector
> > >     DofMap
> > That would work.
>
> ok. This will also have consequences for the file format for
> input/output of Functions.

Yes. Slightly related, I'd like to add output for MeshFuction<T> if the 
T is suitable for output.

> Anyway, the Function class needs some work. We've also talked about
> smart pointers before so there are a few things to figure out:
>
>     - Incorporate DofMap
>     - Reference counting/smart pointers
>     - FiniteElement --> ufc::finite_element
>
> > > I haven't looked closely on the DofMap yet, but does it allow working
> > > only through the on-the-fly computed dofmap of the FFC generated code?
> > This is exactly what it does at the moment.
> >
> > DofMap::dofmap(int dof_map[], const Cell& cell, const uint e = 0) const;
> >
> > just call the FFC nodemap() function. The DofMap can have two finite 
> > elements attached to it (for rows and columns), so e indicates which map 
> > you want.
>
> Sounds good. But I'd like to avoid talking about rows and columns if
> possible.

You don't see this in the code - just a hint in the comments that one 
element should correspond to the test element and the other to the trial 
element.

> > > Or is it necessary to compute all the data?
> > You only need to compute something if you want to know the total number 
> > of degrees of freedom or you want to the sparsity pattern.
> >
> > I'll add shortly the possibility to run the Cuthill-McKee over the map 
> > and reorder it. This will be an option.
>
> What is Cuthill-McKee?

It's the most common reordering algorithm. It will probably improve the 
sparse matrix performance.

> > > I'd like something where one can decide whether to actually build all
> > > the data or just use what FFC generates (to save memory in storing the
> > > function).
> > Agree.My intention is that the data is built only if a renumbering is 
> > requested.
> >
> > What is worthwhile is computing the sparsity pattern. For 10^6 
> > triangles, it only cost 2.5s to do this on my laptop and it can save a 
> > lot of memory.
>
> Very nice.
>
> It looks like estimateNonZeros() is no longer needed in FEM?

I think that I already removed it. FEM::size(uint e) should also be 
removed and DofMap::size(uint e = 0) should be used instead. This 
requires some work though because FEM::size() is used elsewhere in the code.

Garth

> /Anders
> _______________________________________________
> DOLFIN-dev mailing list
> DOLFIN-dev@xxxxxxxxxx
> http://www.fenics.org/mailman/listinfo/dolfin-dev