Draw angle on a MATLAB figure

I want to be able to select a random point on a graph, and then draw a dotted line that goes from the origin to that point, and then a dotted line that goes from that point straight down towards the x-axis, and then this is the part I do not know how to do... I want to draw that little arc symbol with a greek letter indicating the angle that the first line makes with the x-axis. How do I do that?

Something similar to that little green arc, with a greek letter right next to it. Thank you!

Answer 1

[Alan Stevens]

Something like this:

x = [0 1]; y = [0 1.5];
theta = atan(y(2)/x(2));
th = 0:1/360:theta;  r = 0.1;
xx = r*cos(th); yy = r*sin(th);
plot(x,y,xx,yy),grid
axis([0 2 0 2])
text(r,r,'\theta')