Re: Problem with Schur decomposition

[Patrick Alken]

Note that the documentation says:

"If T is desired, it is stored in the upper portion of A on output".

This means that the gsl_eigen_nonsymm / gsl_eigen_nonsymm_Z functions do
not zero out the lower portion of the output matrix. The lower portion
of A is used as temporary workspace by the eigenvalue solver, so the
values stored here should not be referenced. You can explicitly set the
lower portion of A to zero with the function:

gsl_linalg_hessenberg_set_zero()

to get the behavior you want.

Patrick

On 5/18/21 3:05 PM, david allen wrote:
> What is supposed to be a upper quasi-triangular matrix has non-zero
> elements below the first sub-diagonal. This is demonstrated in the
> attached file. Computer and OS information are also in the file.
>