Maintaining explicit diversity within individual ant colonies
Marcus Randall · Bond University Research Portal (Bond University) · 2005
Natural ants have the property that they will follow one another along a trail between the nest and the food source (and vice versa). While this is a desirable biological property, it can lead to stagnation behaviour within artificial systems that solve combinatorial optimisation problems. Although the evaporation of pheromone within local update rules, mutating pheromone values or the bounding of pheromone values may alleviate this, they are only implicit forms of diversification within a colony. Hence, there is no guarantee that stagnation will not occur. In this paper, a new explicit diversification measure is devised that balances between the restriction and freedom of incorporating various solution components. In terms of the target applications, the travelling salesman problem and quadratic assignment problem, this form of diversification allows for the comparison of sequences of common solution components. If an ant is considered too close to another member of the colony, it is explicitly forced to select another component. This restriction may also be lifted if necessary as part of the aspiration criteria. The results reveal improved performance over a control ant colony system