% T84e.m

format compact
clc
clear

N = [1];
syms s;
Ds = expand ((s+1)*(s+2)*(s+3))     % expand pole terms to poly expression
% Ds = s^3+6*s^2+11*s+6
D = poly([-1 -2 -3])                % convert poles to polynomial vector
G = tf (N, D)
rlocus (G)

% Select system gain
disp ('stability condition: K < 60')
K = input ('Enter K: ');

% Bode plot
figure     % for new window
bode (K*G)

% checking specific values on Bode Plot
w = input ('Enter w: ')
Gjw = evalfr (K*G, j*w);
Gmag = abs(Gjw),  Garg = angle(Gjw) * 180/pi
dB = 20 * log10(Gmag)

% closed loop poles
T = K*G / (1 + K*G)
Tmr = minreal (T)
closed_loop_poles = pole (Tmr)

% Nyquist plot
figure
nyquist (K*G)

% Compute system margins
[gm,pm,wg,wp] = margin (K*G)
gm_dB = 20 * log10(gm)

% Nichols diagram
figure
nichols (K*G)

% pause for the user and remove figures
display ('Hit Enter to continue');
pause
close all