What Does Control Theory Have to Offer

5W, 5 E INTRODUCE a few definitions. We have a system, in our examples simple linear difference or differential equations connecting certain inputs and outputs. There is a control variable which should enable us to produce some desired output. The output is the controlled variable. Open loop control exists where the output has no effect upon the input. Feedback provides the means of feeding back the output in order to enable a comparison with the desired output. Closed loop control means a system where output has effect on the input in order to obtain the desired result. Adaptive systems take change^in the environment into account, especially stochastic variations.