Sub-optimal Hankel norm approximation for the analytic class of infinite-dimensional systems

The sub-optimal Hankel norm approximation problem is solved under the assumptions that the system is given in terms of a triple of operators (-A, B, C), where -A is the infinitesimal generator of an exponentially stable, analytic semigroup on the Hilbert space Z,B (element of) L (C m ,Z (alpha)) where -1<(alpha) <= 0,C (element of) L is obtained in terms of the system parameters-A, B, C. (Z, Cp ), and the system is approximately controllable. An explicit parameterization of all solutions is obtained in terms of the system parameters –A,B,C.