1. Why and how to regulate

1.1 Automatic control objectives

To regulate a quantity is to obtain a given behavior from it, in an environment likely to present variations. This initial definition of a much-used but ambiguous word will be refined at a later date. As for environmental variations, they are often neither predictable nor measurable.

Let's clarify a few points right away.

• We will only be looking at automatic systems, i.e. where a machine performs the control function, either to replace a human operator, or because a human operator is unable to achieve the desired result. This requires the calculation and application of commands.

• The physical quantities controlled vary continuously...