代码：
n = [-5:5]; x = (-0.9).^n; % x(n) =
k = -200:200;
w = (pi/100)*k; % [0,pi] axis divided into 101 points.
X = x * (exp(-j*pi/100)) .^ (n'*k);
magX = abs(X); angX = angle(X); realX = real(X); imagX = imag(X);
set(gcf,'Color','white');
subplot(2,2,1); plot(w/pi,magX); grid on; axis([-2,2,0,15]);
title('Magnitude Part');
xlabel('frequency in pi units'); ylabel('Magnitude |X|');
subplot(2,2,3); plot(w/pi, angX/pi); grid on; axis([-2,2,-1,1]);
title('Angle Part');
xlabel('frequency in pi units'); ylabel('Radians/pi');
subplot('2,2,2'); plot(w/pi, realX); grid on;
title('Real Part');
xlabel('frequency in pi units'); ylabel('Real');
subplot('2,2,4'); plot(w/pi, imagX); grid on;
title('Imaginary Part');
xlabel('frequency in pi units'); ylabel('Imaginary');
运行结果：
