Function harmonic 

pub(crate) fn harmonic(
    p: i32,
    m: i32,
    k: Complex,
    geometry: Option<(f64, [f64; 3])>,
    radial: RadialJet,
) -> CartesianTranslation

z_p(k r) P_p^m(cos theta) exp(i m phi) and its displacement and wavenumber derivatives, from the radial jet at k r and the displacement’s direction (None at the origin and at subnormal displacements).