how can i use legend command when i am using hold on for plotting graphs? in my plot i want to use legend command to indicate the color for respective plot that is black for low pass,blue for high pass,green for power complementary,red for all pass.

k = input('Number of frequency points = ');     %%256
w = 0:pi/k:pi;
alpha=0.3

num=((1-alpha)/2)*[1 1]
den=[1 -alpha]
hlp=freqz(num,den,w)

num1=((1+alpha)/2)*[1 -1]
den1=[1 -alpha]
hhp=freqz(num1,den1,w)

figure
subplot(2,1,1)
plot(w/pi, abs(hlp),'k','LineWidth', 2);hold on
grid on;
xlabel('\omega/\pi', 'FontSize', 12, 'FontWeight', 'Bold')
ylabel('Amplitude', 'FontSize', 12, 'FontWeight', 'Bold')
title('|H(\omega)|', 'FontSize', 12, 'FontWeight', 'Bold')
set(gca, 'FontSize', 14, 'FontWeight', 'Bold')

legend ('low pass','high pass','all pass','Location', 'Northwest')
set(legend,'FontSize',7);

subplot(2,1,2)
plot(w/pi, angle(hlp),'k', 'LineWidth', 2);hold on;
grid on;
xlabel('\omega/\pi', 'FontSize', 12, 'FontWeight', 'Bold')
ylabel('Phase, radians', 'FontSize', 12, 'FontWeight', 'Bold')
title('\angle H(\omega)', 'FontSize', 12, 'FontWeight', 'Bold')
set(gca, 'FontSize', 14, 'FontWeight', 'Bold')
% legend (ax2,'hlp','hhp','all_pass','Location', 'Northwest')
% set(legend,'FontSize',7);

subplot(2,1,1)
plot(w/pi, abs(hhp), 'LineWidth', 2);hold on
grid on;
xlabel('\omega/\pi', 'FontSize', 12, 'FontWeight', 'Bold')
ylabel('Amplitude', 'FontSize', 12, 'FontWeight', 'Bold')
title('|H(\omega)|', 'FontSize', 12, 'FontWeight', 'Bold')
set(gca, 'FontSize', 14, 'FontWeight', 'Bold')

subplot(2,1,2)
plot(w/pi, angle(hhp), 'LineWidth', 2);hold on;
grid on;
xlabel('\omega/\pi', 'FontSize', 12, 'FontWeight', 'Bold')
ylabel('Phase, radians', 'FontSize', 12, 'FontWeight', 'Bold')
title('\angle H(\omega)', 'FontSize', 12, 'FontWeight', 'Bold')
set(gca, 'FontSize', 14, 'FontWeight', 'Bold')

all_pass=abs(hlp+hhp)
%figure
subplot(2,1,1)
plot(w/pi, abs(all_pass),'r', 'LineWidth', 2);hold on
grid on;
xlabel('\omega/\pi', 'FontSize', 12, 'FontWeight', 'Bold')
ylabel('Amplitude', 'FontSize', 12, 'FontWeight', 'Bold')
title('|H(\omega)|', 'FontSize', 12, 'FontWeight', 'Bold')
set(gca, 'FontSize', 14, 'FontWeight', 'Bold')

subplot(2,1,2)
plot(w/pi, angle(all_pass),'r', 'LineWidth', 2);hold on;
grid on;
xlabel('\omega/\pi', 'FontSize', 12, 'FontWeight', 'Bold')
ylabel('Phase, radians', 'FontSize', 12, 'FontWeight', 'Bold')
title('\angle H(\omega)', 'FontSize', 12, 'FontWeight', 'Bold')
set(gca, 'FontSize', 14, 'FontWeight', 'Bold')

%%power complentary
powr=(abs(hhp).^2)+(abs(hlp).^2)

figure
subplot(2,1,1)
plot(w/pi, abs(hlp),'k', 'LineWidth', 2);hold on;
grid on;
xlabel('\omega/\pi', 'FontSize', 12, 'FontWeight', 'Bold')
ylabel('Amplitude', 'FontSize', 12, 'FontWeight', 'Bold')
title('|H(\omega)|','FontSize', 12, 'FontWeight', 'Bold')
set(gca, 'FontSize', 14, 'FontWeight', 'Bold')
legend ('hlp','hhp','powr','Location', 'Northwest')
set(legend,'FontSize',7);

subplot(2,1,2)
plot(w/pi, angle(hlp),'k', 'LineWidth', 2);hold on;
grid on;
xlabel('\omega/\pi', 'FontSize', 12, 'FontWeight', 'Bold')
ylabel('Phase, radians', 'FontSize', 12, 'FontWeight', 'Bold')
title('\angle H(\omega)', 'FontSize', 12, 'FontWeight', 'Bold')
set(gca, 'FontSize', 14, 'FontWeight', 'Bold')
legend ('hlp','hhp','powr','Location', 'Northwest')
set(legend,'FontSize',7);

subplot(2,1,1)
plot(w/pi, abs(hhp), 'LineWidth', 2);hold on
grid on;
xlabel('\omega/\pi', 'FontSize', 12, 'FontWeight', 'Bold')
ylabel('Amplitude', 'FontSize', 12, 'FontWeight', 'Bold')
title('|H(\omega)|', 'FontSize', 12, 'FontWeight', 'Bold')
set(gca, 'FontSize', 14, 'FontWeight', 'Bold')

subplot(2,1,2)
plot(w/pi, angle(hhp), 'LineWidth', 2);hold on;
grid on;
xlabel('\omega/\pi', 'FontSize', 12, 'FontWeight', 'Bold')
ylabel('Phase, radians', 'FontSize', 12, 'FontWeight', 'Bold')
title('\angle H(\omega)', 'FontSize', 12, 'FontWeight', 'Bold')
set(gca, 'FontSize', 14, 'FontWeight', 'Bold')

subplot(2,1,1)
plot(w/pi, abs(powr),'g', 'LineWidth', 2);hold on
grid on;
xlabel('\omega/\pi', 'FontSize', 12, 'FontWeight', 'Bold')
ylabel('Amplitude', 'FontSize', 12, 'FontWeight', 'Bold')
title('|H(\omega)|', 'FontSize', 12, 'FontWeight', 'Bold')
set(gca, 'FontSize', 14, 'FontWeight', 'Bold')

subplot(2,1,2)
plot(w/pi, angle(powr),'g', 'LineWidth', 2);hold on;
grid on;
xlabel('\omega/\pi', 'FontSize', 12, 'FontWeight', 'Bold')
ylabel('Phase, radians', 'FontSize', 12, 'FontWeight', 'Bold')
title('\angle H(\omega)', 'FontSize', 12, 'FontWeight', 'Bold')
set(gca, 'FontSize', 14, 'FontWeight', 'Bold')

Answer 1

[Azzi Abdelmalek]

Use the legend function after the three plots

close all
k = input('Number of frequency points = ');     %%256
w = 0:pi/k:pi;
alpha=0.3
num=((1-alpha)/2)*[1 1]
den=[1 -alpha]
hlp=freqz(num,den,w)
num1=((1+alpha)/2)*[1 -1]
den1=[1 -alpha]
hhp=freqz(num1,den1,w)
figure
subplot(2,1,1)
plot(w/pi, abs(hlp),'k','LineWidth', 2);hold on
grid on;
xlabel('\omega/\pi', 'FontSize', 12, 'FontWeight', 'Bold')
ylabel('Amplitude', 'FontSize', 12, 'FontWeight', 'Bold')
title('|H(\omega)|', 'FontSize', 12, 'FontWeight', 'Bold')
set(gca, 'FontSize', 14, 'FontWeight', 'Bold')
plot(w/pi, abs(hhp), 'LineWidth', 2);hold on
grid on;
xlabel('\omega/\pi', 'FontSize', 12, 'FontWeight', 'Bold')
ylabel('Amplitude', 'FontSize', 12, 'FontWeight', 'Bold')
title('|H(\omega)|', 'FontSize', 12, 'FontWeight', 'Bold')
set(gca, 'FontSize', 14, 'FontWeight', 'Bold')
plot(w/pi, abs(all_pass),'r', 'LineWidth', 2);hold on
grid on;
xlabel('\omega/\pi', 'FontSize', 12, 'FontWeight', 'Bold')
ylabel('Amplitude', 'FontSize', 12, 'FontWeight', 'Bold')
title('|H(\omega)|', 'FontSize', 12, 'FontWeight', 'Bold')
set(gca, 'FontSize', 14, 'FontWeight', 'Bold')
legend ('low pass','high pass','all pass','Location', 'Northwest')
set(legend,'FontSize',7);

[s]

Thanks a lot.It worked.

[Mebin Cherian]

But what is we are plotting results from an iteration, and the number f iteration is specified during execution of the code?