Create an ellipse at 45 degree angle

I am trying to create an ellipse of 1 standard deviation around the mean of a scatter plot. The scatter plot is a smear of points at a 45 degree angle.

I'm able to create an ellipse using:

rectangle('Position',cnr,'Curvature',[1,1]);

Where 'cnr' is [x y w h] of the ellpse, with the xy being the lower left corner of where the rectangle would start, but I haven't found anything on how to rotate the ellipse.

Thank you for any help you can give.

Answer 1

[Star Strider]

I experiment with using the rotate funciotn on the rectangle and it wouldn’t move at all.

Try this instead —

v = linspace(0, 1);
rx = 0.5;
ry = 0.25;
x = rx*cos(2*pi*v + pi/4);
y = ry*sin(2*pi*v);

figure
plot(x, y)
grid
axis([-1  1    -1  1])
axis('equal')

Mak e appropriate changes to get the result you want.

.

[Michelle Patrick-Krueger]

That worked perfectly! I feel quite stupid now that you've shown me how easy it was. Thank you, I am very grateful for your help.

[Torsten]

I think a rotation by 45 degrees should be like this:

v = linspace(0, 1);
rx = 0.5;
ry = 0.25;
x = rx*cos(2*pi*v); 
y = ry*sin(2*pi*v);

xx = x*cosd(45) - y*sind(45);
yy = x*sind(45) + y*cosd(45);

figure
plot(xx, yy)
grid
axis([-1  1    -1  1])
axis('equal')

[Star Strider]

@Michelle Patrick-Krueger — As always, my pleasure!!

@Torsten — Noted. Thank you!

.