dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Sun, Sep 12, 2010 at 11:37:26AM +0100, Garth N. Wells wrote:
>
>
> On 11/09/10 16:39, Evan Lezar wrote:
> >New question #125019 on DOLFIN:
> >https://answers.launchpad.net/dolfin/+question/125019
> >
> >Hi
> >
> >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.
>
> I don't think that this is a big deal. The reduction in size will
> almost always be very small.
>
> 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.
> >
>
> There are two ways to apply Dirichlet boundary conditions in DOLFIN.
> I expect if you use 'assemble_system' that you'll get what you want.

Wouldn't that just have the effect of making the bc application
symmetric? The unity eigenvalues would still be there.

--
Anders