Function combine 

pub(crate) fn combine(
    k: Complex,
    (r, unit): (f64, [f64; 3]),
    radial: RadialJet,
    value: Complex,
    tangent: [Complex; 3],
) -> CartesianTranslation

z_p(k r) Y and its displacement and wavenumber derivatives away from the origin, from the unit-sphere harmonic Y at the direction unit and its tangential gradient (see crate::special::tangent).