Several numerical algorithms , such as Generalized Iterative Scaling ( GIS ) ( Darroch and Ratcliff 1972 ) , Improved Iterative Scaling ( IIS ) ( Della Pietra , Della Pietra , and Lafferty 1997 ) , and the Limitedmemory Broyden-Fletcher-Goldfarb-Shanno method ( L-BFGS ) ( Nocedal and Wright