ABSTRACT
Mankind has always made more or less descriptive models of the environment, which often have been used to solve problems or to obtain knowledge about how nature is functioning. When we use mathematics as a useful tool in our description of nature, we talk about mathematical models in contrast to physical models, which try to imitate the physical appearance of the modeled object, for instance, a model of a ship. Models attempt to provide a simplified picture of reality and will never be able to contain all the features of the real system, because then it would be the real system itself. It is, however, important that the model contains the characteristics of the system that are essential in the context of the management or scientific problem to be solved or comprehended.
