Visualisation of the combinatorial effects within evolutionary algorithms: the compass plot

Abstract

Applications of evolutionary algorithms (EAs) to real-world problems are usually hindered due to parameterisation issues and computational efficiency. This paper shows how the combinatorial effects related to the parameterisation issues of EAs can be visualised and extracted by the so-called compass plot. This new plot is inspired by the traditional Chinese compass used for navigation and geomantic detection. We demonstrate the value of the proposed compass plot in two scenarios with application to the optimal design of the Hanoi water distribution system. One is to identify the dominant parameters in the well-known NSGA-II. The other is to seek the efficient combinations of search operators embedded in Borg, which uses an ensemble of search operators by auto-adapting their use at runtime to fit an optimisation problem. As such, the implicit and vital interdependency among parameters and search operators can be intuitively demonstrated and identified. In particular, the compass plot revealed some counter-intuitive relationships among the algorithm parameters that led to a considerable change in performance. The information extracted, in turn, facilitates a deeper understanding of EAs and better practices for real-world cases, which eventually leads to more cost-effective decision-making. HIGHLIGHTS A new tool, called the compass plot, is proposed for visualising the combinatorial effects related to evolutionary algorithms.; The compass plot helps identify key factors and corresponding values for a given problem.; Applications to the optimal design of water distribution systems provide new insights into NSGA-II and Borg.;

Keywords

• combinatorial effects
• evolutionary algorithms
• parameterisation
• visualisation
• water distribution systems