This paper describes the multi-dimensional Non-Local Thermodynamic Equ
ilibrium (NLTE) simulation code GLF. GLF simulates those physical proc
esses needed for modeling X-ray lasers: atomic kinetics, radiation tra
nsport, hydrodynamics and basic laser-plasma interactions. GLF is cons
tructed to be modular, portable and efficient. This paper concentrates
on the physical formulations and numerical methods used in GLF.