coeff_split
returns a named list of coordinates from a vector of
harmonic coefficients. For instance, harmonic coefficients are arranged in
the $coe
slot of Coe
-objects in that way: \(A_1, \dots,
A_n, B_1, \dots, B_n, C_1, \dots, C_n, D_1, \dots, D-n\) after an elliptical
Fourier analysis (see efourier and efourier) while \(C_n
and D_n\) harmonic are absent for radii variation and tangent angle
approaches (see rfourier and tfourier respectively). This
function is used internally but might be of interest elwewhere.