1. GENERAL INTRODUCTION Automatic control has played a vital role in the advance of engineering and sciences. In addition to its extreme importance in space vehicle systems, missile-guidance systems, robotic systems, etc, automatic control has become an important and integral part of modern manufacturing and industrial processes. Say for example, Automatic control is essential in the numerical control of machine tools as utilized in manufacturing industries, in the design of autopilot systems, in the aerospace industries and in the design of cars and trucks in the automobile industries. It is also essential in such industrial operations and more, most engineers and scientists must now have a good understanding of this field.