c75.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

% Step 1: Determine n
             Wp=10; Ws=20; Gp=-2; Gs=-20
             P1=-Gs/10;  P2=-Gp/10; Wsp=Ws/Wp;
             Nc=log((10^P1-1)/(10^P2-1))/(2*log(Wsp));;
             N=ceil(Nc)
% Step 2: Detremine Wc                
            Wc=Wp/(10^P2-1)^(1/(2*N));
            % Alternate cutoff frequency
            % Wc=Ws/(10^P1-1)^(1/(2*N));          
% Step 3: Determine the normalized transfer function H(s)
            for k=1:N
            A=(2*(k-1)+N+1)/(2*N);
            Sk=cos(A*pi)+j*sin(A*pi);
            s=[s Sk];
            end
            s=s';
            num1=[0 1];    den1=poly([s']);
% Step 4: Determine the final filter transfer function H(s)
            num2=[0 Wc^N]; den2=poly(Wc*[s']);
            fprintf('filter order is n=%i\n',N)
            fprintf('cutoff frequency of the filter is Wc=%4f\n',Wc)
            disp('Poles of the transfer function are'),s
            disp('The normalized fourth order transfer function is')
            printsys(abs(num1),abs(den1))
            disp('The transfer function with s replaced by s/Wc is')
            printsys(abs(num2),abs(den2))
% Step 5: Amplitude response of the filter
            w=0:0.01:40; w=w';
            [mag,phase,w]=bode(num2,den2,w);
            plot(w,mag);