To liberate the developer of the physical diffusion model from the task to discretize the corresponding partial differential equation system, PROMIS-NT has been equipped with built-in algorithms to discretize the transport equations (4.1) and (4.2) and boundary models (4.7) and (4.8), respectively. Thereby the task of implementing new diffusion models is reduced to the development of algorithms which compute appropriate values and derivatives for the needed coefficients of (4.1) - (4.8).