上代码：
w = [0:1:500]*pi/500; % freqency between 0 and +pi, [0,pi] axis divided into 501 points.
H = exp(j*w) ./ (exp(j*w) - 0.9 * ones(1,501));
magH = abs(H); angH = angle(H); realH = real(H); imagH = imag(H);
%% --------------------------------------------------------------------
%% START H's mag ang real imag
%% --------------------------------------------------------------------
figure('NumberTitle', 'off', 'Name', 'H its Magnitude and Angle, Real and Imaginary Part');
set(gcf,'Color','white');
subplot(2,2,1); plot(w/pi,magH); grid on; axis([0,1,0,10]);
title('Magnitude Part');
xlabel('frequency in pi units'); ylabel('Magnitude |H|');
subplot(2,2,3); plot(w/pi, angH/pi); grid on; % axis([-1,1,-1,1]);
title('Angle Part');
xlabel('frequency in pi units'); ylabel('Radians/pi');
subplot('2,2,2'); plot(w/pi, realH); grid on;
title('Real Part');
xlabel('frequency in pi units'); ylabel('Real');
subplot('2,2,4'); plot(w/pi, imagH); grid on;
title('Imaginary Part');
xlabel('frequency in pi units'); ylabel('Imaginary');
%% -------------------------------------------------------------------
%% END X's mag ang real imag
%% -------------------------------------------------------------------
运行结果：
