In the common case of a circuit in which the components' values are constant and don't change with time, an alternate definition of linearity is that when a sinusoidal input voltage or current of frequency f is applied, any steady-state output of the circuit (the current through any component, or the voltage between any two points) is also sinusoidal with frequency f.[1][4] A linear circuit with constant component values is called linear time-invariant (LTI).