Could you give a precise definition for "Control Law"?
A control law, which is usually part of the controller, takes the output of a process one wants to control as input. This input is then used in an algorithm to compute an output u, which is sent to the actuating mechanism to perform a corrective action. For example, in a cruise control system, the control law compares the reference speed to the current speed and uses this error (vr - v) in a PID control algorithm to determine the signal u that is then sent to the actuators to decrease the error between the desired and actual speed.
--Luis Soto 15:49, 10 October 2007 (PDT)