subplot(1,1,1)
n = -5:5; x = (-0.9).^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);grid
axis([-2,2,0,15])
xlabel('frequency in units of pi'); ylabel('|X|')
title('Magnitude Part')
subplot(2,1,2); plot(w/pi,angX)/pi;grid
axis([-2,2,-1,1])
xlabel('frequency in units of pi'); ylabel('radians/pi')
title('Angle Part')