Parameterization of suboptimal solutions of the Nehari problem for infinite-dimensional systems

The Nehari problem plays an important role in [H.sup.[infinity]] control theory. It is well known that [H.sup.[infinity]] control problem can be reduced to solving this problem. This note gives a parameterization of all suboptimal solutions of the Nehari problem for a class of infinite-dimensional systems. Many earlier solutions of this problem are seen to be special cases of this new parameterization. It is also shown that for finite impulse response systems this parameterization takes a particularly simple form. Index Terms--Delay systems, [H.sup.[infinity]]-control, infinite-dimensional systems, Nehari problem.