c125.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=8/35;Ws=15/35;Gp=-2;Gs=-11;T=pi/35;

% Digital Lowpass Butterworth

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

% Digital Cheby1

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

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

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



 W=0:.001: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