Function inv_bessel_i_ratio_1m_impl 

pub fn inv_bessel_i_ratio_1m_impl<P, E, V>(t: V, nu: V) -> V
where
    P: Policy,
    E: FloatElement,
    V: FloatVector<Element = E> + PrimalProjection<Primal = V> + SpecializedSpecialMath<E>,

The kappa with 1 - A_nu(kappa) = t, for 0 < t <= 2 (t = 1 - r), the complement form of inv_bessel_i_ratio_impl: well conditioned as t -> 0, where the plain form loses 2 kappa eps / (p - 1) to the rounding of r.