A system takes an input signal and produces an output signal. It is called linear when it obeys two rules: homogeneity (scaling the input scales the output by the same amount) and additivity (the response to a sum of inputs equals the sum of the individual responses). This page lets you pick a linear system and different input signals, then compares both sides of each rule so you can see the two properties hold.
Every plot below sends its input through the system T you select here, producing the output signal y(t).
Scale the input by a factor a before the system, or scale the output by a after the system — a linear system gives the same result either way. Pick an input signal and drag the slider to change a.
Add two signals before the system, or send each one through separately and add the outputs — a linear system gives the same result either way. Pick the two input signals to combine.
