Variance-Reduction Techniques

Abstract

In this chapter, we discuss various techniques which may be used to make calculations more efficient. In some cases, these techniques require that no further approximations be made to the transport physics. In other cases, the gains in computing speed come at the cost of computing results which may be less accurate since approximations are introduced. The techniques may be divided into 3 categories: those that concern electron transport only, those that concern photon transport only, and other more general methods. The set of techniques we discuss does not represent an exhaustive list. There is much reference material available, and we only cite a few of them^1–5. An especially rich source of references is McGrath and Crawford’s report³ which contains an annotated bibliography. Instead, we shall concentrate on techniques that have been of considerable use to the authors and their close colleagues. However, it is appropriate to discuss briefly what we are trying to accomplish by employing variance-reduction techniques.