This equation computes the y-component of the radius of gyration for an nth degree parabola, convex up, where the equation for the parabola is y = `(h/b^(1/n)) x^(1/n)`
The radius of gyration `r_y` is the y-component of the distance from the reference axis at which all of the area can be considered to be concentrated to produce the moment of inertia.