%MATLAB PROGRAM p201
%Butterworth analog lowpass prototype
n=0:0.01:2;
N=10
[z,p,k]=buttap(N);
[b,a]=zp2tf(z,p,k);%Zero-pole to transfer function conversion.
[H,w]=freqs(b,a,n);%returns the complex frequency response vector H of the filter b/a:
magH=(abs(H)).^2;
plot(w,magH);
axis([0 2 0 1]);%AXIS([XMIN XMAX YMIN YMAX]) sets scaling for the x- and y-axes on the current plot
xlabel('w/wc');
ylabel('|H(jw)|^2');
title('Butterworth analog filter prototype');
grid