close all;
clear all;
L3 = tf(20,[1 1])*tf(1,[0.5 1])*tf(1,[2 1]);

w = logspace(log10(0.001),3,1000);
[s_r,s_i] = nyquist(L3,w);

s_r = s_r(:);
s_i = s_i(:);
s_s = s_r+s_i*i;
plot(s_s,'b-','linewidth',2);
hold on;
plot(-1,0,'r+','linewidth',2);


plot(-1,0,'r+','linewidth',2);
xlabel('Re','fontsize',16);
ylabel('Im','fontsize',16);
title('Nyquist Diagram','fontsize',16);
set(gca,'YTick',[-100 0 100]);
set(gca,'XTick',[-100 -1 0 100]);

plot(s_s(400),'b^','Linewidth',6);

grid;
axis([-5,25,-15,5]);
