% Example file of phase and gain margins

% Plot Gain and Phase Margins of Transfer Function

close all, clc

%% First example, create a continuous transfer function

Gs = tf(1,[1 2 1 0])

figure, margin(Gs) % plots gain and phase margins

[Gm,Pm] = margin(Gs) % returns the values of Gm and Pm 

figure, nyquist(Gs) % Nyquist diagram plot

%% Second example: stable

Hs = tf([2 5 1],[1 2 3])

figure, nyquist(Hs)

[Gm,Pm] = margin(Hs)

%% Third example: marginally stable

K = 100; % K = 60 -> marginally stable

Ls = tf([0 0 0 K],[1 6 11 6])

figure, nyquist(Ls)

[Gm,Pm] = margin(Ls)