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[Garth Wells <question125019@xxxxxxxxxxxxxxxxxxxxx>]

Question #125019 on DOLFIN changed:
https://answers.launchpad.net/dolfin/+question/125019

    Status: Open => Answered

Garth Wells proposed the following answer:

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.

Garth

> Any thoughts or assistance would be greatly appreciated.
>
> Thanks Evan
>
> PS. I know that I have asked this before, but due to other projects
> requiring my attention, I have not been able to focus on this and
> achieve a proper solution.
>

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