%----------------------------------------------------------------------------
% exa070500_1.m,  for fig. 7.5.4,
%----------------------------------------------------------------------------
clear all;

% 梳狀濾波器的頻率響應和極零圖；
M=4096;
r=0.9;
b=[1 0 0 0 0 0 0 0 -1];
a=[1 0 0 0 0 0 0 0 -r];
[h,f]=freqz(b,a,4*M,'whole',1); 

subplot(221);
zplane(b,a);

subplot(222)
plot(f,(1+r)*abs(h)/2);grid;