henhen

G = tf([20],[1 5 6 0])
figure(1)
subplot(2,1,1)
bode(G)
subplot(2,1,2)
nyquist(G)


K=0.85;
Gf = feedback(G,K)
% figure(2)
% subplot(2,1,1)
% nyquist(Gf)
% subplot(2,1,2)
% bode(Gf)

K_margin = db2mag(-6.01)
G_margin = Gf*K_margin
G_1 = Gf*0.6
G_2 = Gf*0.4
figure(3)
subplot(2,1,1)
nyquist(G_1)
subplot(2,1,2)
nyquist(G_2)
% G1_fb = feedback(G,1)
% Gm_fb = feedback(G,K_margin)
% G2_fb = feedback(G,0.5)
% subplot(3,1,3)
% step(G2_fb)






% G1 = zpk([20],[1 5 6 0])
% figure(3)
% nyquist(G1)