ABSTRACT
The major reason for adopting a deterministic quantitative approach to process response modelling is that between them Newton and Liebnitz provided a special set of techniques for dealing with rates of change, the differential calculus. The great progress of classical physics in the first part of the nineteenth century, stemming from Newton’s law of gravitation and fully developed by Laplace and Lagrange, depended entirely on simplification and abstraction and rested in the belief that the universe was rationally constructed. The response of the system to various kinds of input is determined by the nature of the differential equations which describe it and systems are classified in terms of the order of these equations and the typical temporal response they produce. The ultimate goal is to obtain the laws which define the system from completely theoretical assumptions, so that the output is defined for any input.
