Introduction

Fundamentals and principles of the anisotropic gaseous model are presented in this chapter so as to give the description of the numerical approach employed to model stellar clusters, as we shall see in next chapters. We start with a brief description of the mathematical basis which can be regarded as a short summary of the description of kinetic theory in chapter eight of BT87. The reader interested in an in-depth study is addressed to it. On the other hand, we stress on the peculiarities of the approximation we make use of, the so-called local approximation, so as to be aware of the restrictions of our theory and emphasise them. Later, we will give the set of equations describing the system, the interaction terms to be taken into consideration to represent realistic models, like mass exchange by mass loss, heating, loss-cone, exchange of kinetic energy between the stellar system and the interstellar gas via drag forces, etc, to be included in the right-hand terms of this set. Ensuingly we shall make a thoughtfully depiction of the gaseous component in the cluster and their own interaction terms.