3.2 Approximate model function
Generally, the structure of the relationship between the response and the independent
variables is unknown. The first step in RSM is to find a suitable approximation to
the true relationship. The most common forms are low-order polynomials (first or
second-order).
In this thesis a new approach using genetic programming is suggested. The
advantage is that the structure of the approximation is not assumed in advance, but is
given as part of the solution, thus leading to a function structure of the best possible
quality. In addition, the complexity of the function is not limited to a polynomial but
can be generalised with the inclusion of any mathematical operator (e.g