Determine the expansion coefficients of a function for a given set of input Slepian functions.

## Usage

falpha = SlepianCoeffs(galpha, flm, nmax)

## Returns

falpha : float, dimension (nmax)
A vector containing the Slepian coefficients of the input function flm.

## Parameters

galpha : float, dimension ((lmax+1)**2, nmax)
An array containing the spherical harmonic coefficients of the Slepian functions, where lmax is the spherical harmonic bandwidth of the functions. Each column corresponds to a single function of which the spherical harmonic coefficients can be unpacked with SHVectorToCilm.
flm : float, dimension (2, lmax+1, lmax+1)
The spherical harmonic coefficients of the global function to be expanded in Slepian functions.
nmax : integer
The number of expansion coefficients to compute.

## Description

SlepianCoeffs will compute the Slepian coefficients of a global input function flm given the Slepian functions galpha. The Slepian functions are determined by a call to either (1) SHReturnTapers and then SHRotateTapers, or (2) SHReturnTapersMap. Each row of galpha contains the (lmax+1)**2 spherical harmonic coefficients of a Slepian function that can be unpacked using SHVectorToCilm. The Slepian functions must be normalized to have unit power (that is the sum of the coefficients squared is 1), and the Slepian coefficients are calculated as

f_alpha = sum_{lm}^{lmax} f_lm g(alpha)_lm