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+//Example 8.12
+clc;clear;close;
+rp=0.9                        //passband ripple
+rs=0.2                        //stopband ripple
+wp=%pi/2;                     //passband frequency
+ws=3*%pi/4;                   //stopband frequency
+T=1;
+fp=2/T*tan(wp/2);
+fs=2/T*tan(ws/2);
+s=poly(0,'s');
+z=poly(0,'z');
+hs=1;
+//Calculating the order of filter
+num=log((rs^-2 -1)/(rp^-2 -1));
+den=2*log(fs/fp);
+N=ceil(num/den);
+
+//Calculation of cut-off frequency
+fc=fp/(rp^-2 -1)^(0.5/N);
+
+//Calculating filter response
+if modulo(N,2)==1 then
+    hs=hs*fc/(s+fc);
+end
+for k=1:N/2
+    b=2*sin((2*k-1)*%pi/(2*N));
+    hs=hs*fc^2/(s^2+b*fc*s+fc^2);
+end
+hs=clean(hs);
+sys=syslin('c',hs);             
+hz=ss2tf(cls2dls(tf2ss(sys),T));        //converting H(s) to H(z)
+
+//Displaying filter response
+[hzm,fr]=frmag(hz,256);
+disp(hz,'Filter Transfer function: ');
+plot(fr,hzm);
+title('Lowpass Butterworth Filter Response');ylabel('Amplitude-->');xlabel('Normalised frequency f/fs-->');
+\ No newline at end of file