b = [0.0181,  0.0543, 0.0543,  0.0181];a = [1.0000, -1.7600, 1.1829, -0.2781];m = 0:length(b)-1; l = 0:length(a)-1;K = 500; k = 1:1:K;w = pi*k/K;  % [0, pi] axis divided into 501 points.num = b * exp(-j*m'*w); % Numerator calculationsden = a * exp(-j*l'*w); % Denominator calculationsH = 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 pi units'); ylabel('|H|');title('Magnitude Response');subplot(2,1,2); plot(w/pi,angH/pi); gridxlabel('frequency in pi units'); ylabel('Phase in pi Radians');title('Phase Response');