Worst case analysis in the frequency domain: The H∞approach to control

This paper describes an approach to frequency domain design using H
^x
methods. We outline the main tools available and describe how these methods can be applied to control problems and to some gain optimization problems in circuits. In particular, we present a new method for combining several competing constraints which arise in control (such as tracking error and bandwidth constraints) into a single type of constraint which
H^{\infty}
methods analyze explicitly. A computer program which implements and teaches this method is on tape for a VAX. It is available on request.