function q = blocus

 % Metodo di Adams-Moulton a 2 passi (ordine 3)

   ro   = [1 -1 0];
   sig  = [5 8 -1]/12;
 
 % Backward Differentiation Formula (BDF) a 2 passi (ordine 2)

%   ro   = [1 -4/3  1/3];
%   sig  = [2 0 0]/3;

 % Metodo BDF a 3 passi (ordine 3)

%   ro   = [1 -18/11  9/11 -2/11];
%   sig  = [6 0 0 0]/11;

   z = exp(sqrt(-1)*[0:.01:2*pi]);    
   q = polyval(ro,z)./polyval(sig,z);