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%---------------------------------------------------------------------------- 
% exa030203, for example 3.2.5 
% to explain how to do DTFT 
%---------------------------------------------------------------------------- 
clear; 
 
% 产生一指数信号； 
N=128; 
a=0.6; 
for n=1:N 
   x(n)=a^(n-1); 
end 
 
% 实际上是对该信号作DFT: 
X=fft(x); 
 
Xa=abs(X); 
Xp=angle(X); 
Xp=unwrap(Xp); 
w=-0.5+1/N:1/N:0.5;    
subplot(221) 
plot(w,fftshift(Xa));grid on; 
subplot(222) 
plot(w,fftshift(Xp));grid on;