Function inv_bessel_i_ratio_impl 

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

The kappa >= 0 with I_nu(kappa) / I_{nu-1}(kappa) = r, for 0 <= r < 1. Odd in r.