Chapter 



12 



THE ERROR-CONTROLLED 

 REGULATOR 



12/1. In the previous chapter we studied the nature of regulation, 

 and showed that certain relations and laws must hold if regulation 

 is to be achieved. There we assumed that regulation was achieved, 

 and then studied what was necessary. This point of view, however, 

 though useful, hardly corresponds with that commonly used in 

 practice. Let us change to a new point of view. 



In practice, the question of regulation usually arises in this way: 

 The essential variables E are given, and also given is the set of states 

 T] in which they must be maintained if the organism is to survive (or 

 the industrial plant to run satisfactorily). These two must be given 

 before all else. Before any regulation can be undertaken or even 

 discussed, we must know what is important and what is wanted. Any 

 particular species has its requirements given — the cat must keep itself 

 dry, the fish must keep itself wet. A servo-mechanism has its aim 

 given by other considerations — one must keep an incubating room 

 hot, another must keep a refrigerating room cold. Throughout 

 this book it is assumed that outside considerations have already 

 determined what is to be the goal, i.e. what are the acceptable 

 states 7]. Our concern, within the book, is solely with the problem 

 of how to achieve the goal in spite of disturbances and difficulties. 



The disturbances D threaten to drive E outside the set rj. If D 

 acts through some dynamic system (an environment) T, then the 

 diagram of immediate effects is initially 



D 



The organism (or whoever is interested in E), however, has some 

 power of forming another dynamic system R (e.g. a brain or a servo- 

 mechanism) which can be coupled to T and which, if properly 

 made, will form with T a whole, F, so that the diagram of immediate 

 effects becomes 



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