G0=tf(1,[1,3,3,1]); P=[0.1 0.3 0.5 1 2 3]; 
hold on 
for i=1:length(P) 
G=feedback(P(i)*G0,1); 
step(G);grid on, 
axis([0,12,0,1.3]) 
end 
hold off 
figure, rlocus(G0) 
axis([-2,0.2,-2,2]) 
k=rlocfind(G0) 
Select a point in the graphics window 
selected_point =-0.0000 + 1.7357i 
k =8.0380