Abstract: The invention is directed to a simulation and modelling approach, which comprises two parts. The first part comprises a generic mathematical model used to simulate or model a system and elements of the system interacting with a predetermined environment. The second part comprises at least one user defined data file that contains not only predetermined parameters (scalars values and/or tables with fixed independent variables) for use by the first part, but which also contains executable mathematical equations and respective data relating to an element of the system. These user-defined algorithmic expressions add to and complement the generic mathematical model so as to produce, when operating together numerical output that simulates or models the behaviour of the one or more elements of the system in a predetermined environment. Typically computer programs interact with the invention to provide a visualisation tools for the numerical output provided.