Orbital ordering (OO) in La<Subscript>0.5</Subscript>Sr<Subscript>1.5</Subscript>MnO<Subscript>4</S ubscript> has been studied using soft X-ray resonant diffraction (SXRD) at the Mn L<Subscript>2,3</Subscript> edges in combination with many-body cluster calculations. The SXRD intensity is modelled in second quantization using a small planar cluster consisting of a central active Mn site...</subscript><//s></subscript></subscript></subscript>