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

## Usage

index = YilmIndexVector (i, l, m)

## Returns

index : integer
Index of an 1D array of spherical harmonic coefficients corresponding to i, l, and m.

## Parameters

i : integer
1 corresponds to the cosine coefficient cilm[0,:,:], and 2 corresponds to the sine coefficient cilm[1,:,:].
l : integer
The spherical harmonic degree.
m : 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.