When invoked without lefthand arguments, margin produces a Bode plot and displays the margins on this plot. The frequency at which the magnitude is 1.0 is called the unity-gain frequency or crossover frequency. It is generally found that gain margins of three or more combined with phase margins between 30 and 60 degrees result in reasonable trade-offs between bandwidth and stability. Wcg and Wcp , given the SISO open-loop model sys . When faced with several crossover frequencies, margin returns the smallest gain and phase margins.
Interpolation is performed between the frequency points to estimate the margin values.
This approach is generally less accurate. The phase margin is computed using theory, and the gain margin by solving for the frequency .