Function bessel_i0_impl 

pub fn bessel_i0_impl<P, V, const NS: usize, const NL: usize, const NF: usize, const SCALED: bool>(
    x: V,
    t: &BesselI<V::Element, NS, NL, NF>,
) -> V
where
    V: FloatVector + TranscendentalMathWithPolicy,
    P: Policy,

$I_0(x)$, or $e^{-|x|} I_0(x)$ when SCALED.

Even in x, so the sign is dropped up front and never restored.