Function periodic_to_cw_matrix 

pub fn periodic_to_cw_matrix(
    destination: Basis,
    source: Basis,
    ks: [Complex; 2],
    period: f64,
    helicity: bool,
) -> Result<(DMatrix<Complex>, PeriodicToCwResidual)>

Outgoing cylindrical expansion of a z-periodic spherical source array. Axial Fourier wavenumbers are independent inputs; compose kz=kpar+2pin/period for diffraction orders.

Upstream: treams.operators.expandlattice from a spherical to a cylindrical basis. Differences: treams pairs each axis only with the sphere chain of the same position index and ignores the positions; this matrix couples every axis with every chain through the translation between them.