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% MATLAB script for Illustrative Problem 4, Chapter 1. 
echo on 
n=[-20:1:20]; 
% Fourier series coefficients of x(t) vector  
x=.5*(sinc(n/2)).^2; 
% sampling interval 
ts=1/40; 
% time vector 
t=[-.5:ts:1.5]; 
% impulse response 
fs=1/ts; 
h=[zeros(1,20),t(21:61),zeros(1,20)]; 
% transfer function 
H=fft(h)/fs; 
% frequency resolution 
df=fs/80; 
f=[0:df:fs]-fs/2; 
% rearrange H 
H1=fftshift(H); 
y=x.*H1(21:61); 
% Plotting commands follow.