Function complete_elliptic_e 

pub fn complete_elliptic_e(m: f64) -> f64

The complete elliptic integral of the second kind, E(m), for m in [0, 1].

Computed by the arithmetic-geometric mean, which converges quadratically: the number of correct digits doubles each iteration, so f64 accuracy costs about seven steps regardless of m.

E(0) = pi/2 (a circle) and E(1) = 1 (a degenerate ellipse, a doubled line segment).