GPS-X Technical Reference

17 Modelling Fundamentals
Experiment
Model
An experiment is the process of extracting data from a system through manipulation of
the inputs.
Experimentation is probably the single most important concept of a system; for it is
through experimentation that we develop a better understanding of it. Experimentation
implies that two basic properties of a system are being used:
1. Controllability, and
2. Observability
To perform an experiment implies the application of a set of external conditions to the
inputs of a system (i.e. the accessible inputs) and observe the reaction of the system by
recording the behaviour of the outputs (i.e. the accessible outputs). This is where some of
the advantages of a system begin to appear. One of the major advantages of
experimenting with a "simulated" system as opposed to the "actual" or "real" system, is
that real systems are usually under the influence of a large number of additional
inaccessible inputs (i.e., disturbances) and that a number of useful outputs may not be
available through measurement (i.e., they are internal states of the system).
One of the major motivations for simulation is that in the simulation world, all inputs and
outputs are accessible. This allows the execution of simulations that lie outside the range
of experiments that are applicable to the real system.
A model is an
abstraction of a
system
One definition of a model is: A model is an approximation of a system to which an
experiment can be applied to answer questions about the system.
A model does not imply a computer program. We should be clear to distinguish between
a model and a computer program. A model could be a piece of hardware or simply an
understanding of how a system works. Models are often coded into computer programs.
Why is Modelling Important
Modelling means the process of organizing knowledge about a given system. By
performing experiments, knowledge about a system is gathered. In the beginning the
knowledge is unstructured. By understanding the cause and effect relationships and
by placing observation in both a temporal and spatial order, the knowledge gathered
during the experiment is organized. Thus, the system is better understood by the
process of modelling.
GPS-X Technical Reference