%----------------------------------------------------------------------------
% exa070500_2.m,   for fig. 7.5.5
%----------------------------------------------------------------------------
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,M,'whole',1); 
%hb=impz(b,a,31);
subplot(221);
zplane(b,a);
%stem(hb);
subplot(222)
plot(f,(1-r)*abs(h)/2);grid;