Re: Good eigenvalue/eigenvector test problems for eigs?

[David Bateman]

Sebastien Loisel wrote:
>
>     ## Symmetric real PD
>     A = spdiags([ones(n,1),4*ones(n,1),ones(n,1)],[-2,0,2],n,n);
>
>
> This should not be ill conditioned. A-2I is diagonally dominant and
> symmetric so all its eigenvalues are positive. 6I-A is also diagonally
> dominant and symmetric so its eigenvalues are all positive. As a
> result, the eigenvalues of A are between 2 and 6, this is a pretty
> tight bound. The condition number is uniformly bounded by 3.
>
> Sebastien Loisel
This was my thinking as well, the the problem should be easy. By try the
code I supplied under matlab and see what you get for "det(A - lamba *
eye(n))".

D.

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