Why does a circle plotted in MATLAB appear as an ellipse?

Question

I wonder in MATLAB how I would plot a circle and show it correctly instead of by default showing it as an ellipse. I guess it has something to do with the local coordinate system in the axis.

Answer 1

You can use the command axis equal to set the data units to be the same on each axis. Here's an example:

theta = linspace(0, 2*pi, 100);
subplot(121);                     % Show the default plot
plot(cos(theta), sin(theta));
title('Default axes settings');
subplot(122);                     % Show a plot with equal data units
plot(cos(theta), sin(theta));
title('Equalized tick spacing');
axis equal;

Answer 2

In addition to using axis equal as @gnovice suggested, you can turn off the stretch-to-fill feature by using daspect:

daspect manual

or even setting the axes aspect ratios explicitly to:

daspect([1 1 1])