일때,  을 구하고, 주기성을 조사해보자.

ex3_5.cem

subplot(1,1,1)
n = 0:10; x = (0.9*exp(j*pi/3)).^n;
k = -200:200; w = (pi/100)*k;
X = x * (exp(-j*pi/100)) .^ (n'*k);
magX = abs(X); angX =angle(X);
subplot(2,1,1); plot(w/pi,magX);
xtitle("frequency in units of pi"); ytitle("|X|")title("Magnitude Part")subplot(2,1,2); plot(w/pi,angX/pi);
xtitle("frequency in units of pi'); ylabel('radians/pi");
title("Angle Part");