clear all;%ap=2;as=10;wp=20;ws=30;ap=input('Enter value of passband attenuation: ');as=input('Enter value of stopband attenuation: ');wp=input('Enter passband frequency: ');ws=input('Enter stopband frequency: ');N=ceil(log(sqrt((10.^(0.1*as)-1)/(10.^(0.1*ap)-1)))/log(ws/wp));[z,p,k]=buttap(N);[Num,Den]=zp2tf(z,p,k);h=freqs(Num,Den);w=logspace(-2,2,length(h));

subplot(2,1,1);loglog(w,abs(h));title('Magnitude');subplot(2,1,2);semilogx(w,angle(h));title('Phase');