Investigating problem hardness of real life applications

This chapter represents a first attempt to characterize the fitness landscapes of real-life Genetic Programming applications by means of a predictive algebraic difficulty indicator. The indicator used is the Negative Slope Coefficient, whose efficacy has been recently empirically demonstrated on a large set of hand-tailored theoretical test functions and well known GP benchmarks. The real-life problems studied belong to the field of Biomedical applications and consist of automatically assessing a mathematical relationship between a set of molecular descriptors from a given dataset of drugs and some important pharmacokinetic parameters. The parameters considered here are Human Oral Bioavailability, Median Oral Lethal Dose, and Plasma Protein Binding levels. The availability of good prediction tools for pharmacokinetics parameters like these is critical for optimizing the efficiency of therapies, maximizing medical success rate and minimizing toxic effects. The experimental results presented in this chapter show that the Negative Slope Coefficient seems to be a reasonable tool to characterize the difficulty of these problems, and can be used to choose the most effective Genetic Programming configuration (fitness function, representation, parameters' values) from a set of given ones.