Function agm_complete_ke 

pub fn agm_complete_ke<P, E, V>(k: V) -> (V, V)
where
    P: Policy,
    E: FloatElement,
    V: FloatVector<Element = E>,

Complete elliptic integrals of the first and second kind, (K(k), E(k)), evaluated together from a single AGM pass (they share the iteration).

K(k) = pi / (2 * AGM(1, k')),     k' = sqrt(1 - k^2)
E(k) = K(k) * (1 - sum_{n>=0} 2^{n-1} c_n^2)

Valid for |k| <= 1; |k| > 1 gives NaN. The endpoint |k| = 1 is pinned to (inf, 1) under check_overflow. See the note at the end of the function.