A∞ and AN formulations of the linear transport equation in heterogeneous media

The aim of the paper is to provide a contribution for the extension to heterogeneous media of the A∞ and AN formulations for the linear transport equation. A new approach is proposed, in which the exponential of the optical length is decomposed in a sum of pure exponential terms, as in a homogeneous medium; in this way, a set of coupled diffusion-like equations is obtained. Different approximations are presented and their validity is discussed.