dolfin team mailing list archive

[kent-and@xxxxxxxxx]

> 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.

Kent

> (2) The eigenvectors associated with these only have non-zero
> coefficients for the relevant boundary degrees of freedom -- hence can
> be filtered by examining the coefficients
> (3) The krylov-schur solver in SLEPc 3.1(-p2) converges way more often
> than before. This makes solving non-tiny singular, generalized
> eigenvalue problems way easier.
>
> --
> Marie
>
>
>
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