[Trilinos-Users] anasazi and eigs with singular matrix

[Simone Deparis]

Hi Heidi,

Thornquist, Heidi K wrote:
> Hi Simone,
> 
> Yes, we have experience with this type of problem.  In fact, an example
> for solving something similar
> to this can be found in BlockKrylovSchurEpetraExGen.cpp.  

thank you, I look through this.

> What specific eigenvalues are you looking to
> compute for this generalized problem (Ax = \lambda Bx), i.e. largest
> magnitude, smallest magnitude, rightmost?

Actually I'll work with the symmetrized version of A: (A+A^T)/2 and B is 
already simmetric.
I look for the larger and the two smallest (in magnitude) eigenvalue + 
vector.

> I would be glad to help you set this up.  If you want to take a look at
> the example, we can start there.

Thank you. I have to finish to set up my matrices and run some tests and 
then I'll start with the eigsproblem.

Thank you
Simone
PS: I add here some answers to David:

 > Another question:
 > How accurate do the eigenvectors need to be?

I need an accurate upper bound for the largest and accurate lower bounds 
for the smallest ones. But since I am realistic, I take what I get :-)

 > Are you checking that the inf-sup bound?

Do you mean the inf-sup lower bound? Among others.
I have a set of matrices A, each independend one from an other and they 
are undefinite. The only helping bit is that since I simmetrize, the 
eigs will be real.




> Hello,
> 
> I have an eigenvalue problem of the form Ax = \lambda B x
> 
> where B is a singular matrix (positive semidefinite).
> I am interested in modes orthogonal to the zero mode and I whish to use
> the Anasazi::BlockKrylovSchur method.
> 
> Does somebody have an experience with something similar?
> 
> Thank you
> Simone
> 
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