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[Lapack] [lapackers] bug in DGEHRD



On Thu, 22 Apr 2010, James Demmel wrote:

There is a permutation that makes this matrix 2x2 block triangular,

Mmm, I can not find this permutation ... I tried symamd and colamd and 
they can not either.

Note that while
   [V,D]=eig(A);
does not work,
   [Q,H]=hess(A);
   [V,D]=eig(H);
   V = Q*V;
works ...

Definetley balancing ... I've just remembered that actually you can 
desactivate balancing in eig of matlab, all relative backward errors are 
back to 1e-16 with [V,D]=eig(A,'nobalance');.

Julien.


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