Calculating arc length of an ellipse

My goal is to calculate the arc length of an ellipse from 0 to pi/2. The ellipse is centered at the origin and the horizontal radius is 'a' and vertical radius is 'b'. Now I was told that the way to do this was to use matlab's elliptic integral functions. That being said I fail to see how I could use these functions to solve this problem, I have looked over the documentation about this functions and don't see how they could be used. Is it possible to solve this problem using the elliptic integral functions in matlab? (ellipke(m) function)

[Torsten]

If you write down the formula for the arc length, just replace cos^2(x) by 1-sin^2(x) and you'll soon arrive at an elliptic integral.

[Amply]

I just end up with sqrt([(a^2)*(sin^2(theta))]+(b^2)-[(b^2)*(sin^2(theta))])

[Torsten]

https://math.stackexchange.com/questions/2108199/arc-length-of-an-ellipse-using-integration

[Amply]

Okay, I ended up getting sqrt{1-[1-(a^2/b^2)]*sin^2(t)}. Which is the elliptic integral form with my K^2 being (1-a^2/b^2), I don't know why it was so difficult for me to grasp but finally got it. Thank you!