The Dominance Tournament Method of Monitoring Progress in Coevolution Speaker: Lin, Wei-Kai (2009/04/30) 1

Outline  Introduction  Experiments and Results  Discussion and Future Work  Conclusions 2

Introduction 3  We want to know if an arms race took place  Master Tournament (Cliff and Miller 1995; Floreano and Nol 1997) is the most common analysis method  Every generation champion is compared to every other generation champion  Results show whether wins increase over generations  But does that demonstrate an arms race?  Dominance Tournament  Test problem: neural network and robot duel

Master Tournament The champion of every generation is compared with the champion of all (prior) generations Count the number of wins The higher the generation, the more opponents the champion can beat 4

Master Tournament - Shortcomings  The computational complexty  Tournament between all generations: C(n, 2)  Does it really progress? 46 5

Dominance Tournament  The first dominant strategy is the champion of the first generation.  A generation champion is a dominant strategy if it is superior to all previous dominant strategies 6

NEAT and Robot Duel  The test problem  Neuro Evolution of Augmenting Topologies (NEAT)  Adding new structure to existing network, or  Evolving only fixed topologies  Robot Duel  Eat food to gain energy  The robot with higher energy wins if two robots collide  Two food positions is randomly chosen (from total 144 configurations) 7

Experiments and Results  The two population setup for competitive coevolution  Using master tournament and dominance tournament  Analysis the results in a single run 8

Competitive Coevolution Setup 9  Two populations  Host: the population currently being evaluated  Parasite: the population from which opponents is chosen  The opponents set consists of  Best strategies in 4 species in the parasite population  8 strategies chosen randomly from a Hall of Fame  A single fitness evaluation includes two trials  Starts from the east and the west position.

Monitoring Progress 10  Champion: the winner of the best strategies in two populations in a generation in 288 trials  Master Tournament  A champion plays all other champions in 2 trial  Dominance Tournament  144 x 2 = 288 trials between a dominant strategy and a champion

Results 11

Dominance Tournament Results 12

Observations from Dominance Tournament 13  The progress after 200 generations  Higher level of dominance takes more time to reach  The 17 th dominant strategy won 221/288 trials (compared with the 14 th level in the fixed topology)  Circularities discovered  A champion is able to defeat some but not all of dominant strategies  Complexifying and fixed topology occurs 48 and 93 times  Dominance tournament takes 738 comparisons, but master tournament takes 124,750

Discussion and Future Work 14  For multiple runs, such analysis can also be applied  The highest level of dominance  Equivalent dominance level  Equivalent generation  Other population statistic: the network complexity  The initialization of the first dominant strategy  The first champion: natural and poor enough  The first champion that defeats serveral champions from the first few generations

Dominance Tournament with Different Roles 15  New dominant strategy must defeat all previous dominant strategies from opposing population  Ranking alternates

Conclusion 16  The tournament dominance provides specific details necessary for drawing strong conclusions  The best individual is well defined  We are able to conclude that the arms race continued  Lower computational complexity  Test specific claims by making comparisons between different runs