'Angular diameter distance between objects at 2 redshifts.
Useful for gravitational lensing.
Parameters
z1, z2 : array-like, shape (N,)
Input redshifts. z2 must be large than z1.
Returns
d : `~astropy.units.Quantity`, shape (N,) or single if input scalar
The angular diameter distance between each input redshift
pair.'

def angular_diameter_distance_z1z2(self, z1, z2):

    z1 = np.asanyarray(z1)
    z2 = np.asanyarray(z2)
    return (self._comoving_transverse_distance_z1z2(z1, z2) / (1.0 + z2))
