Aurentz, Jared L.; Mach, Thomas; Vandebril, Raf; Watkins, David S.
(Electronic Transactions on Numerical Analysis, 2015)
A fast Fortran implementation of a variant of Gragg's unitary Hessenberg QR algorithm is presented. It is proved, moreover, that all QR- And QZ-like algorithms for the unitary eigenvalue problems are equivalent. The algorithm ...