Why is the line of y2 always a flat line at x-axis instead of a straight line with negative gradient?

x = linspace(0, 20, 100);
y1 = (exp(x)-1)/10;
y2 = -x+3;
plot(x, y1, 'r');
hold on;
plot(x, y2, 'g');
xlabel('Diode Voltage');
ylabel('Diode Current');
title('Plot of I_D and V_D');

Answer 1

[Image Analyst]

It's flat because of hte scale of your y axis. Look -- it goes from -1 to 50 million, while y2 goes from 3 to -17. How do you expect the line to look when it only changes height of 20 in a scale of 50 million?

If you want to see y2, plot it on a separate axes.

[Rubayet]

However, I have to show them on the same plot to find their intersecting point. This is why I used hold on. Can I change the limit of y axis?

[Rubayet]

Found it, ylim([LL,UL]),

Thanks for your help!

[Image Analyst]

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Answer 2

[Walter Roberson]

x = linspace(0, 20, 100);
y1 = (exp(x)-1)/10;
y2 = -x+3;
%plot(x, y1, 'r');
hold on;
plot(x, y2, 'g');
xlabel('Diode Voltage');
ylabel('Diode Current');
title('Plot of I_D and V_D');

Which is to say that your y1 goes up to about 5 x 10^7. If we were to guess that the plot is about 500 pixels high then that would mean that there would be 5e7/5e2 = 1e5 data units per pixel. Your y2 covers about 20 data units, so on the scale of 0 to 5*10^7 it occupies about 20/1e5 = 0.0002 pixels of y difference. Which is not enough to be visible.

[Rubayet]

Thanks a lot for your explanation. I did not see the highest value of y-axis and hence could not analyse it before. It worked out now using the function ylim.

Wish you a good day!