© 1997 by Institute of Mathematics and its Applications
New results on the operator Carleson measure criterion
Department of Mathematics, Iowa State University Ames, Iowa 50011, USA
Department of Electrical Engineering, Ben-Gurion University Beer Sheva 84105, Israel
We consider control systems of the form
= Ax + Bu where A is the generator of a diagonal semigroup T on l2 and B is an unbounded operator from a Hilbert space U to l2. In a previous paper by Hansen & Weiss, a condition called the operator Carleson measure criterion was shown to be necessary for the admissibility of the control operator B. Furthermore this condition was shown to be sufficient if T is either analytic or invertible. In this paper we continue the analysis of admissibility as related to the operator Carleson measure criterion. We show that the operator Carleson measure criterion is satisfied if and only if the input-to-state transfer function has a certain decay rate. We also extend the previous sufficiency results of Hansen & Weiss to a more general class of diagonal semigroups. To achieve our aims, we derive some general results (not confined to diagonal semigroups) concerning Lypapunow equations and feedback-type perturbations, which are of independent interest.
Keywords: Admissibility; Carleson measure; Lyapunov equation.