c127.m

matlab例程MATLAB 6.x版的内建数据类型（Built-in data type）就有5种以上

% Wp=[1000 2000];Ws=[450 4000]. Divide by normalizing factor pi/T=10^4 to obtain
% normalized values Wp=[0.1 0.2] and Ws=[0.045 0.4]. Also Gp=-2.1;Gs=-20. 


Wp=[0.1 0.2];Ws=[0.045 0.4];Gp=-2.1;Gs=-20

% Digital Bandpass Butterworth Filter


[N,Wn]=buttord(Wp,Ws,-Gp,-Gs)
[b,a]=butter(N,Wn)

% Digital Bandpass Cheby1 Filter


%[N,Wn]=cheb1ord(Wp,Ws,-Gp,-Gs)
%[b,a]=cheby1(N,-Gp,Wn)

% Digital Bandpass Cheby2 (inverse Cheby) Filter

%[N,Wn]=cheb2ord(Wp,Ws,-Gp,-Gs)
%[b,a]=cheby2(N,-Gs,Wn)

% Digital Bandpass Elliptic Filter

%[N,Wn]=ellipord(Wp,Ws,-Gp,-Gs)
%[b,a]=ellip(N,-Gp,-Gs,Wn)


W=0:.01:pi;W=W';
%freqz(b,a,W)
T=pi/10^4;
 W=0:.01:pi;W=W';
          H=freqz(b,a,W);
          w=W/T;
          mag=abs(H);
          phase=180/pi*unwrap(angle(H));
          subplot(2,1,1);
          plot(w,mag);grid;
          subplot(2,1,2);
          plot(w,phase);grid