ABSTRACT
This chapter discusses a number of topics essential to an understanding of parts of the
book, but which may not be well understood by the typical reader with an engineering
education.
33.2 SOME TERMS FROM MATHEMATICS
A model is a quantitative description of the behaviour of a system, developed to predict
its quantitative performance in new situations and/or to illuminate the workings of the
system under existing conditions. Controlled experiments, physical analogues and
mathematical functions are common devices used as models to represent reality.
Macroscopic models use data aggregated across at least two non-homogeneous categories
within the system. Microscopic models only aggregate across homogeneous categories.
An endogenous variable is one determined within the model under consideration, whereas
an exogenous variable is one determined outside the model. A stochastic variable is one
varying randomly with time and a stochastic model is one containing stochastic variables.
A deterministic model is one that does not include random variables.
