Compute the rotation matrix d(pi/2) used in rotating data expressed in spherical harmonics.

## Usage

dj = djpi2 (lmax)

## Returns

dj : float, dimension (lmax+1, lmax+1, lmax+1)
The rotation matrix dj(pi/2).

## Parameters

lmax : integer
The maximum spherical harmonic degree of the spherical harmonic rotation.

## Description

djpi2 will calculate the rotation matrix d_{mM}^j (pi/2) that is used in rotating spherical harmonics in the routines SHRotateRealCoef and SHRotateCoef.

This routine is based on code originally written by Guy Masters.