Regulation as an interpolation problem Original Research Article

The design of a controller such that the closed-loop system will track reference signals or reject disturbance signals from a specified class is known as the “servomechanism problem” or the “regulator problem.” We show here that the regulator problem can be looked at as an interpolation problem for a subspace-valued function that can be viewed as a multivariable version of the Nyquist curve. The result is applied to obtain a simple parametrization of all solutions.