[Octave-bug-tracker] [bug #42097] 64bit Slackware, eig returning incorrect results

[Russell Carden]

Follow-up Comment #19, bug #42097 (project octave):

I almost have all the code in place to do what you are suggesting.
I will do that later this afternoon.
However, let me note The results are incorrect immediately after the call to
DGEEV.  The eigenvalues and the eigenvectors are incorrect.  If you compute
the perturbation to A, as I did in a previous comment,  you find that the
presenece of the A(3,1) entry results in a perturbation to the A(2,1) entry of
the matrix.  This perturbation is not a linear function of the A(3,1) entry.
I just did a test on a similarly structured matrix 
A=diag(ones(3,1),1), A(4,1)=1.  eig(A) returns incorrect results,
However when I apply eig(A^2) which is not an upper Hessenberg matrix, I get
correct results.  Octave always seems to give the right answer for upper
Hessenberg matrices.



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