Notion of system

The notion of a system is not easy to define. It seems simpler to us to try to approach this notion from its various attributes. Thus, we can say that a system is "something" that transforms certain quantities u _i (t ), called input quantities, into certain others y _j (t ), called output quantities, as shown in figure 1 . This definition is very general. Input quantities u _i (t ) are those which act on the system, while output quantities y _j (t ) are those produced by the system....