clc
wp=0.2*pi;wr=0.3*pi;Ap=1;Ar=15;
T=1;Omegap=(2/T)*tan(wp/2);Omegar=(2/T)*tan(wr/2);
[b,a]=afd_butt(Omegap,Omegar,Ap,Ar)
[C,B,A]=sdir2cas(b,a)
[dB,mag,pha,Omega]=freqs_m(b,a,pi)
[hn,x,t]=impulse(b,a);
subplot(224);  
plot(t,hn)
  title('沖激響應');ylabel('hn(t)');
  xlabel('時間（秒)');

[b,a]=bilinear(b,a,T);
[C,B,A]=dir2cas(b,a);
[db,mag,pha,w]=freqz_m(b,a);
subplot(221);plot(w/pi,mag)
title('數字濾波器幅度響應|H|(ej/Omegar)'); ylabel('|H|');
subplot(222);plot(w/pi,db)
title('數字濾波器幅度響應(db)'); ylabel('分貝數');
subplot(223);plot(w/pi,pha/pi)
title('數字濾波器相位響應'); ylabel('弧度');
  xlabel('以Pi為單位頻率');
delta_w=2*pi/1000;
Ap=-(min(db(1:1:wp/delta_w+1)))
Ar=-round(max(db(delta_w+1:1:501)))