Making the Edge-Set Encoding Fly by Controlling the Biasof its Crossover Operator

The edge-set encoding is a direct tree encoding which applies search oper-ators directly to trees represented as sets of edges. There are two variantsof crossover operators for the edge-set encoding: With heuristics that con-sider the weights of the edges, or without heuristics. Due to a strong biasof the heuristic crossover operator towards the minimum spanning tree(MST) a population of solutions converges quickly towards the MST andEAs using this operator show low performance when used for tree opti-mization problems where the optimal solution is not the MST. This paperpresents a modied crossover operator (-TX) that allows us to controlthe bias towards the MST. The bias can be set arbitrarily between thestrong bias of the heuristic crossover operator, or being unbiased.[...]