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[Kent-Andre Mardal <question125019@xxxxxxxxxxxxxxxxxxxxx>]

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

Kent-Andre Mardal proposed the following answer:

Note that SystemAssembler adds 1 to the element matrices for the
Dirichlet conditions. Where n elements meet the diagonal entry
will be n. Hence, for an eigenvalue problem you will have
a number of eigenvectors associated with the eigenvalues (1,2,...n).
Here, n will depend on the mesh, but it will never be a very large number.
You should exlude these values from you eigenvalue analysis.

Kent


> 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.
>
> Thanks for the help so far.
>
> Evan
>
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