Function periodic_to_cw 

pub fn periodic_to_cw(
    to: Mode,
    from: Mode,
    k: Complex,
    period: f64,
    helicity: bool,
) -> Result<Complex>

Direct outgoing spherical-to-cylindrical coefficient of a z-periodic array.

A negative period gives the coefficient of its absolute value, while periodic_to_cw_matrix rejects period <= 0.

Upstream: treams.sw.periodic_to_cw.