b=[0.0181 0.0543 0.0543 0.0181]
a=[1.000,-1.7600 1.1829 -0.2781]
m=0:length(b)-1;l=0:length(a)-1;
K=500;k=0:1:K;
w=pi*k/K;
num=b*exp(-j*m'*w);
den=a*exp(-j*l'*w);
H=num./den;
magH=abs(H);angH=angle(H);
subplot(1,1,1)
subplot(2,1,1);plot(w/pi,magH);
grid;axis([0,1,0,1])
xlabel('frequency in units of pi');ylabel('|H|');
title('Magnitude Response');
subplot(2,1,2);plot(w/pi,angH/pi);grid;
xlabel('frequency in units of pi');ylabel('phase in pi Radians');
title('Phase Response');