Notion of system

The notions of system and signal are inseparable.

Generally speaking, a system is a set of components arranged to produce a certain result.

Its state is affected by several variables, which are the system's inputs. The result of the action of the inputs on the system is its response, characterized by the behavior of one or more output variables.

If inputs and outputs are functions of time defined at each instant t, we speak of a continuously operating system or, more briefly, a continuous system; if they are only defined at certain discrete instants (operating step number k), we speak of a discrete or recurrent system.

If we consider only one input e (t ) or e (k )...