This s-function captures a sample of two (ideally oscillatory) signals and, using a FFT, computed the amplitude ratio and phase difference between the two signals during a simulation.

This is intended to provide a way to numerically generate nonlinear equivalents of Bode plots for either linear or nonlinear systems. By choosing a frequency of interest (e.g. an input frequency you select), you can compute the amplitude and phase of another signal, like the output of a nonlinear control system, with respect to the input. Bode plots are defined and available only for steady-state linear systems with transfer functions. This function allows you to numerically generate similar plots (after your system reaches dynamic steady state) for linerr or nonlinear systems.