Four-block problem: stable plants and rational weights

Abstract

It is shown that for a large class of multivariable infinite-dimensional stable plants, and rational weights, the four-block problem reduces to finding the singular values of a certain operator defined by Feintuch and Francis (1986), via the singular system which is studied by Foias and Tannenbaum (1988), and Özbay and Tannenbaum (1988).