  We develop a simple tensorial contraction method to obtain analytical formula
for X-ray resonant magnetic scattering. We apply the method considering first
electric dipole-dipole and electric quadrupole-quadrupole scattering in the
isolated atom approximation and compare the results with previous works. Then
we apply the method to derive phenomenological original formulas which account
also for non-spherical systems and for dipole-quadrupole mixing.
