TABLE OF CONTENTS We now have the tools that are necessary to consider the pros and cons of feedback systems. Consider the system of Figure 3.1. What are the "physical implications" of the diagram? Generally speaking G c( s) is the transfer function of an object that we as system designers have added to the system in order to improve the system's performance it is added to compensate the system's shortcomings. The transfer function of the object whose output we are supposed to be controlling is G p( s). It is the given physical plant; we cannot change G p( s). The feedback network's transfer function is H( s). We also design the feedback network.
Though the labeling in the block diagram makes it seem as though all of the inputs and output are of the same sort (say voltages), this need not be the case. When it is the case, it often means that some blocks consist of more than one element. For example, a block that is supposed to be a motor but accepts a voltage input and returns a voltage output clearly consists of a motor and some sort of position (or velocity) to voltage transducer.
Frequently our goal is to design a system such that the output of the system tracks the input as well as possible. That is, we would like to minimize 
. In this case it...
