All optimal Hankel-norm approximations and their /spl Lscr//sub /spl infin// error bounds in discrete-time

This paper investigates a parallel problem to Glover (1984): approximate a multivariable transfer function G(z) of McMillan degree n by G(z) of McMillan degree smaller than k in discrete-time. A state-space solution is derived to the optimal Hankel-norm approximation problem, together with characterization to all optimal Hankel-norm approximations. It is shown that the /spl Lscr//sub /spl infin//error bound derived in holds for discrete-time systems as well.