c128.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

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


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

% Digital Bandstop Butterworth Filter

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

% Digital  Bandstop Cheby1 Filter

%[n,Wn]=cheb1ord(Wp,Ws,-Gp,-Gs);
%[b,a]=cheby1(n,-Gp,Wn,'stop')

% Digital  Bandstop Cheby2 (inverse Cheby) Filter


%[n,Wn]=cheb2ord(Wp,Ws,-Gp,-Gs);
%[b,a]=cheby2(n,-Gs,Wn,'stop')

% Digital  Bandstop Elliptic Filter


%[n,Wn]=ellipord(Wp,Ws,-Gp,-Gs);
%[b,a]=ellip(n,-Gp,-Gs,Wn,'stop')



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