25 Years Ago

Many control objectives can be expressed in terms of a criterion function. Generally, explicit solutions to such optimization problems require full knowledge of the plant and disturbances, and complete freedom in the complexity of the controller. In practice, the plant and the disturbances are seldom known, and it is often desirable to achieve the best possible performance with a controller of prescribed complexity. For example, one may want to tune the parameters of a PID controller in order to extract the best possible performance from such simple controller.