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This paper contains a survey of the computational methods which play an important role in the computer aided design in the frequency domain of single-input/single-output, linear systems, possibly including a pure time delay, and in continuous or discrete time. Emphasis throughout is on those numerical aspects unique to classical control systems design.

In this paper a method for designing dynamic compensators which reduce open loop interaction in a multivariable system is presented. An integral measure of interaction in the frequency domain is minimized to produce possibly dynamic compensators for either the system transfer function or its inverse. The technique is applicable to unstable systems, systems with time delays and, via a class of weighting functions can be used to obtain emphasised interaction reduction in particular frequency ranges. In addition, a feedback configuration aimed at lowering interaction is shown to give rise to a problem functionally equivalent to the above. An example designed interactively by computer is included to illustrate the effectiveness of the procedure.