代码：

%% ------------------------------------------------------------------------%%            Output Info about this m-filefprintf('\n***********************************************************\n');fprintf('        
     
       Exameple 8.18 \n\n');time_stamp = datestr(now, 31);[wkd1, wkd2] = weekday(today, 'long');fprintf('      Now is %20s, and it is %8s  \n\n', time_stamp, wkd2);%% ------------------------------------------------------------------------% Digital Filter Specifications:wp = 0.2*pi;                 % digital passband freq in radws = 0.3*pi;                 % digital stopband freq in radRp = 1;                      % passband ripple in dBAs = 15;                     % stopband attenuation in dB% Analog prototype specifications: Inverse Mapping for frequenciesT = 1; Fs = 1/T;                 % set T = 1OmegaP = (2/T)*tan(wp/2);        % Prewarp(Cutoff) prototype passband freqOmegaS = (2/T)*tan(ws/2);        % Prewarp(cutoff) prototype stopband freq% Analog Chebyshev-1 Prototype Filter Calculation:[cs, ds] = afd_chb1(OmegaP, OmegaS, Rp, As);% Bilinear Transformation:[b, a] = bilinear(cs, ds, T); [C, B, A] = dir2cas(b, a)% Calculation of Frequency Response:[db, mag, pha, grd, ww] = freqz_m(b, a);%% -----------------------------------------------------------------%%                             Plot%% -----------------------------------------------------------------  figure('NumberTitle', 'off', 'Name', 'Exameple 8.18')set(gcf,'Color','white'); M = 1;                          % Omega maxsubplot(2,2,1); plot(ww/pi, mag); axis([0, M, 0, 1.2]); grid on;xlabel(' frequency in \pi units'); ylabel('|H|'); title('Magnitude Response');set(gca, 'XTickMode', 'manual', 'XTick', [0, 0.2, 0.3, M]);set(gca, 'YTickMode', 'manual', 'YTick', [0, 0.1778, 0.8913, 1]);subplot(2,2,2); plot(ww/pi, pha/pi); axis([0, M, -1.1, 1.1]); grid on;xlabel('frequency in \pi nuits'); ylabel('radians in \pi units'); title('Phase Response');set(gca, 'XTickMode', 'manual', 'XTick', [0, 0.2, 0.3, M]);set(gca, 'YTickMode', 'manual', 'YTick', [-1:1:1]);subplot(2,2,3); plot(ww/pi, db); axis([0, M, -30, 10]); grid on;xlabel('frequency in \pi units'); ylabel('Decibels'); title('Magnitude in dB ');set(gca, 'XTickMode', 'manual', 'XTick', [0, 0.2, 0.3, M]);set(gca, 'YTickMode', 'manual', 'YTick', [-30, -15, -1, 0]);subplot(2,2,4); plot(ww/pi, grd); axis([0, M, 0, 15]); grid on;xlabel('frequency in \pi units'); ylabel('Samples'); title('Group Delay');set(gca, 'XTickMode', 'manual', 'XTick', [0, 0.2, 0.3, M]);set(gca, 'YTickMode', 'manual', 'YTick', [0:5:15]);
     

　　运行结果：