Control specification
Several different control strategies have been devised in the past years. These vary from extremely general ones (PID controller), to others devoted to very particular classes of systems (especially robotics or aircraft cruise control). A control problem can have several specifications. Stability, of course, is always present. The controller must ensure that the closed-loop system is stable, regardless of the open-loop stability. A poor choice of controller can even worsen the stability of the open-loop system, which must normally be avoided. Sometimes it would be desired to obtain particular dynamics in the closed loop: that the poles have {\displaystyle Re[\lambda ]<-{\overline {\lambda }}} , where {\displaystyle {\overline {\lambda }}} src="https://wikimedia.org/api/rest_v1/media/math/render/svg/de9d2ee37eb0cd550de8d8f34b9d13700f79384e" style="border: 0px; display: inline-block; height: 3.009ex; margin: 0px; vertical-align: -0.338ex; width: 1.481ex;" /...