Function bessel_in_impl 

pub fn bessel_in_impl<P, E, V, const NS: usize, const NL: usize, const NF: usize, const N: i32, const SCALED: bool>(
    x: V,
    t: &BesselI<E, NS, NL, NF>,
) -> V
where
    E: FloatElement,
    V: FloatVector<Element = E> + TranscendentalMathWithPolicy,
    P: Policy,

$I_N(x)$ for N >= 2, or $e^{-|x|} I_N(x)$ when SCALED.

Thin wrapper over bessel_in_pair_impl, which computes $I_{N-1}$ alongside at no extra cost in the recurrence arm. Callers that want the derivative should take the pair directly.