Re: Good eigenvalue/eigenvector test problems for eigs?

[David Bateman]

Sebastien Loisel wrote:
>     Yes, its supposed to be well behaved, but consider
> 
>     octave:1> n=200;
>     octave:2> A = spdiags([ones(n,1),4*ones(n,1),-ones(n,1)],[-2,0,2],n,n); 
> 
> 
> Ok, that's not the same matrix I was talking about, but it's also well
> conditioned.
> 
>       -7.2806 + 0.0000i
>       -7.1793 + 0.0000i
>       -6.4207 + 0.0000i
>        5.8174 + 0.0000i
>       -5.6617 - 0.1134i
>       -5.6617 + 0.1134i
> 
> 
> That's really weird. I don't get that in Matlab. And it shouldn't even
> be a hard test case... Doesn't the QR iteration work just fine on this
> stuff?
> 
> Sébastien Loisel
> 


Does matlab give the right answer for eig ? I can't check till monday
back at work. On the second non symmetric test case I tried it
definitely didn't..

D.