dolfin team mailing list archive

[Evan Lezar <evanlezar@xxxxxxxxx>]

Kent

Thanks for the reply.  I have started to have a look at the code to make the
changes that you suggested, but must admit that I am a little lost.

I will continue to work on it, but any other tips would be greatly
appreciated.

Thanks
Evan

On Wed, Feb 4, 2009 at 10:50 PM, <kent-and@xxxxxxxxx> wrote:

>
> Hi,
>
> Here are my rough thoughts on it.
>
> In FunctionSpace there is a function restriction which creates a
> (restricted) DofMap based
> on a mesh, a ufc:.dofmap and a MeshFunction. The way I have implemented,
> this function is such that the MeshFunction contains booleans that
> indicates which cells
> that should be used in the DofMap. It could equally well be vertices or
> other
> mesh entities, but the way restriction is implemented now, it has to be
> cells.
> It should however be relatively easy to change it to other entities (I
> think).
> Changing this would give a loc2glob array which contains -1 for the entries
> that should not be used. As I understand, petsc will then avoid these
> entries
> so it might work, at least for petsc, with only this alteration in the
> function restriction.
>
> Kent
>
> > Hi
> >
> > Since I last rasied this issue there have been a lot of changes (great
> > ones
> > I must add) to the fenics codebase, so I thought I would ask again.
> >
> > I am interested in removing the rows and columns of the finite element
> > matrices (for vector electromagnetic problems) associated with zero
> valued
> > Dirichlet boundary conditions.  It is important that the original degrees
> > of
> > freedom (or a mapping between the two sets) be available so that the
> > solution of a system of equations or an eigenvalue problem can be used to
> > visualize the solution, for example.
> >
> > The removal of the degrees of freedom has two advantages that I can think
> > of
> > (for my applications at any rate).  The first is that the systems being
> > solved will be smaller.  The second is of particular concern to me as I
> am
> > often solving eigenvalue problems and the unity eigenvalues that are
> > introduce when applying the Dirichlet BCs in their current form
> > contaminate
> > the spectrum in many of my examples.
> >
> > Any thoughts or assistance would be greatly appreciated.
> >
> > Thanks
> > Evan
> > _______________________________________________
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> >
>
>
>