dolfin team mailing list archive

[kent-and@xxxxxxxxx]

> On Mon, Sep 13, 2010 at 01:16:23PM +0200, kent-and@xxxxxxxxx wrote:
>> > On 13. sep. 2010 08:11, Evan Lezar wrote:
>> >> Question #125019 on DOLFIN changed:
>> >> https://answers.launchpad.net/dolfin/+question/125019
>> >>
>> >>     Status: Answered => Open
>> >>
>> >> Evan Lezar is still having a problem:
>> >> Hi
>> >>
>> >> I think Anders is correct. I have just had a look at the
>> SystemAssembler
>> >> code, and it does seem to also place ones on the diagonals of the
>> matrix
>> >> to which the boundary conditions are being applied. In addition, I am
>> >> not solving a linear system, but eigenvalue problems and as such b is
>> a
>> >> Matrix not a Vector.
>> >>
>> >> At present I am manually removing the rows and columns for the
>> matrices
>> >> that correspond to (zero) Dirichlet conditions and then
>> reconstructing
>> >> the correct solution vector from the eigenvector that I obtain. This
>> is
>> >> fine for testing and getting the rest of the system running.
>> >>
>> >>
>> >
>> >
>> > Is this really simpler than filtering the eigenpairs? As far as I see
>> it
>> >
>> > (1) (As you know) the eigenvalues associated with the boundary
>> > conditions are all 1's
>>
>> The eigenvalues will not only be 1. They will be 1, 2, 3, .. etc
>> depending
>> on then number
>> of cells that meet. They should however be easy to spot and filter out.
>
> Not if the problem solved is a model problem designed to give
> eigenvalues that are 1, 2, 3 etc.
>
> --
> Anders
>

Yes, but you can often choose a scaling that makes these eigenvalues easy
to spot.

Kent