Function polynomial_cw1d 

fn polynomial_cw1d<const N: usize>(
    l: i32,
    n: i32,
    y: Jet<N>,
    beta: Jet<N>,
) -> Jet<N>

The inner sum S_ln of the 1D cylindrical summand of reciprocal_term (upstream _s_sum_cw1d, whose docstring formula omits the factor l! that its code includes) for l = |m|, with y = k r_y (-k r_y for negative m) and beta = q_x / k: sum_s (-y)^(2n - s) beta^(l - s) l! / (2^s (2n - s)! (l - s)! (s - n)!) over s = n..=min(2n, l).