Linear and non-linear operators
The operator specifies the signal transfer, the relationship between the input signal and the output signal of the system.
Now operators are considered from a computer technology perspective. They can be classified as linear and non-linear. In a steady state, a linear operator responds to the same input signal changes with proportional output signal changes. Plotting the steady value of the output signal as a function of the input signal, we get a linear static characteristic curve, a straight line.
In a linear system the process can be easily calculated within and outside the measured, examined range of behaviour, and we can predict the system response in a future point of time or the consequence of the next control setting, as the individual effects simply accumulate. The superposition theorem is valid for linear systems: the responses given to the individual inputs can be calculated separately and then added up.