Compute the index of an 1D array of spherical harmonic coefficients corresponding to i, l, and m.

## Usage

index = YilmIndex (i, l, m)

## Parameters

index : output, integer
Index of an 1D array of spherical harmonic coefficients corresponding to i, l, and m.
i : input, integer
1 corresponds to the cosine coefficient cilm(1,:,:), and 2 corresponds to the sine coefficient cilm(2,:,:).
l : input, integer
The spherical harmonic degree.
m : input, integer
The angular order.

## Description

YilmIndexVector will calculate the index of a 1D vector of spherical harmonic coefficients corresponding to degree l, angular order m and i (1 = cosine, 2 = sine). The elements of the 1D vector array are packed by successive degrees, where each degree lists the l+1 cosine terms and then the l cosine terms. The index is given explicitly by l**2+(i-1)*l+m+1.