The N-Strikes-Out Algorithm: A Steady-State Algorithm for Coevolution
Thomas Miconi, Alastair Channon · 2006
We introduce the N-strikes-out algorithm, a simple steady-state genetic algorithm for competitive coevolution. The algorithm can be summarised as follows: Run competitions between randomly chosen individuals, keep track of the number of defeats for each individual, and remove any individual which has been defeated N times. Naive application of the algorithm in 2-population problems leads to severe disengagement. We find that disengagement can be eliminated (for all tasks involving real-valued continuous scores) by determining 'victories' and 'defeats' between fellow members of the same species, using competitions against a single member of the opposing species as a point of comparison. We apply our algorithm to the "box-grabbing" problem for artificial 3D creatures introduced by Sims. We compare our algorithm with Sims' original Last Elite Opponent algorithm, and describe (and explain) different results obtained with two different implementations differing mainly by the harshness of their selection regimes.