Function bessel_i_ratio_impl 

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

I_nu(x) / I_{nu-1}(x), for x >= 0 and nu >= 1. Odd in x.