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

## Usage

call djpi2 (dj, lmax, exitstatus)

## Parameters

dj : output, real(dp), dimension (lmax+1, lmax+1, lmax+1)
The rotation matrix dj(pi/2).
lmax : input, integer(int32)
The maximum spherical harmonic degree of the spherical harmonic rotation.
exitstatus : output, optional, integer(int32)
If present, instead of executing a STOP when an error is encountered, the variable exitstatus will be returned describing the error. 0 = No errors; 1 = Improper dimensions of input array; 2 = Improper bounds for input variable; 3 = Error allocating memory; 4 = File IO error.

## 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.