p.2 In the closed-loop system, the control u(t) is modified
in some way by information about the behavior of the system output. A feedback system is often better able to cope with unexpected
disturbances and uncertainties about the system's dynamic behavior.
p.4 Engineers and scientists are frequently confronted with the task of
analyzing problems in the real world, synthesizing solutions to these problems, or developing theories to explain them. One
of the first steps in any task is the development of a mathematical model of the phenomenon being studied. This
model must not be oversimplified, or conclusions drawn from it will not be valid in the real world. The model should
not be so complex as to complicate unnecessarily the analysis.
p.27 Most systems considered in classical control theory are feedback control
systems.
p.33 The advantages of feedback control are:
1. The system output can be made to follow or track the specified
input function in an automatic fashion. The name automatic control theory is frequently used for this reason.
2. System performance is less sensitive to variation of parameter values...
3. System performance is less sensitive to unwanted disturbances...
4. Use of feedback makes it easier to achieve the desired transient and steady-state
response
p.41 Since perfect models are never available, either because of intentional
simplifications or because of unavoidable ignorance, time variations, or noise corruption, a good control system must be at
least somewhat forgiving of these errors.
