1 ti = 1e9;
   2 td = .1;
   3 kt = 90.63e-6;
   4 t = 1/20000;
   5 J = 8.6556e-3;
   6  
   7 k = kt; 
   8 kp = k-k*t/(2*ti); 
   9 kd = k*td/t;
  10 ki = k*t/ti;
  11 
  12 num = t^2/(2*J)*[kd+ki+kp,-kd+ki,-kd-kp,kd];
  13 den = [1,-3,3,-1,0];
  14 
  15 hold off;
  16 rlocus(tf(num,den,t));
  17 
  18 tita = 0:0.01*pi:2*pi;
  19 x = sin(tita);
  20 y = cos(tita);
  21 hold on;
  22 plot(x,y,'o1');