An Alternative Approach for Playing Complex Games like Chess. 1Alternative Game Playing Approach Jan Lemeire May 19 th 2008

Pag. Jan Lemeire / 14 2 Alternative Game Playing Approach Research Topics Computer versus Brain Deep Blue: 600 million evaluations/second Chess experts: 10 patterns/second

Pag. Jan Lemeire / 14 Brute force chess playing Most succesful! Evaluation of future states Alternative Game Playing Approach 3

Pag. Jan Lemeire / 14 Alternative game playing approaches Decision-making: used to map states to operators. Explanation-Based Learning (EBL): try to learn the states that lead to advantageous situations. States are identified by patterns. 4 Alternative Game Playing Approach

Pag. Jan Lemeire / 14 Game State Evaluation 5 Alternative Game Playing Approach All approaches rely on a game state evaluation: –measure ‘goodness’ of state Or –to select a good move. My hypothesis is based on a problem with state evaluation.

Pag. Jan Lemeire / 14 6 Alternative Game Playing Approach Example: fork pattern. Opportunity! Fork pattern is way to success! Counter move… Fork pattern does not give an advantage…

Pag. Jan Lemeire / 14 Correct evaluation problem Consider two relevant patterns, P 1 and P 2  evaluation = f(P 1, P 2 )  4 regions in state space should be considered: 7 Alternative Game Playing Approach For example ‘fork’ and ‘make chess’

Pag. Jan Lemeire / 14 Correct evaluation problem Evaluation = f(features or patterns). One has to capture all situations in which the pattern leads to a successful outcome, all counter plans have to be excluded. Evaluation of pattern combinations heavily depends on game context! Features alone do not give us the right information. 8 Alternative Game Playing Approach

Pag. Jan Lemeire / 14 Known problem in literature Deep Blue relied on looking as far as possible into the future and just a simple state evaluation. “However, even simple patterns like a knight fork are non-trivial to formalize…” Fürnkranz “Learning too many too specialized rules with explanation-based learning”, Minton 1984, Epstein, Gelfand and Joanna Lesniak 1996 (HOYLE pattern-based learning). “Even in simple games, such as tic-tac-toe, 45 concepts were learned with 52 exception clauses”, Fawcett and Utgoff

Pag. Jan Lemeire / 14 Hypothesis “The impact of a pattern on the outcome of the game entirely depends on whether or not some states, called the effects, are attained during the continuation of the game.” 10 Alternative Game Playing Approach

Pag. Jan Lemeire / 14 New kind of knowledge Fork  win a piece Weak king’s defense  successful attack on the king Pressure  successful combination E.g. fork bad defense of the king: can we have a successful attack on the king or get an advantage by putting pressure on the king bad defense  pressure  advantage Alternative Game Playing Approach 11 Patterns denote opportunities, advantages have to be verified.

Pag. Jan Lemeire / 14 Alternative game playing 12 Alternative Game Playing Approach Second hypothesis: this works if one can quickly evaluate interfering patterns White recognizes pattern 1: White has to check in game tree whether - a positive effect can be attained: - black can neutralize pattern 1: Hypothesis: More efficient than brute force tree exploration

Pag. Jan Lemeire / 14 Similar to human game playing! Chess experts rely on falsification (Cowley and Byrne, 2004). Humans can easily recognize and identify patterns, but have difficulties formally defining them. Humans can pinpoint the patterns that were decisive in a game, can answer why-questions.  not by current computer game playing Humans can reason about a game. 13 Alternative Game Playing Approach

Pag. Jan Lemeire / 14 Hypothesis requires theoretical or experimental confirmation… 14 Alternative Game Playing Approach Test by simulation of games  no decisive conclusion yet. Pattern engine needed that is able to: Describe patterns Recognize patterns Extract patterns Reason with patterns “White attacks two black pieces with a fork, one of the pieces can make chess. White thus has to move its king and black can bring his second piece into safety.” Theoretical proof?