Othello

1. Othello Sean Farrell April 2, 2014

2. Othello • Two-player game played on 8x8 board • All pieces have one white side and one black side • Initial board setup is shown right, with valid moves marked as dots

3. The Evolution of Strong Othello ProgramsMichael Buro, 2003 • First computer Othello tournaments in 1979 • In 1980, first time a World-champion lost a game of skill against a computer • 6-0 defeat of then human World-champion in 1997

4. Evaluation Function Evolution • Mini-max search used to estimate the chance of winning for the player with current move • Construct function using features of board state that correlate with winning • Important features • Disc stability – stable discs cannot be flipped • Disc mobility – move options • Disc parity – last move opportunities for every empty board region

5. IAGO (1982) • Classic, hand-crafted evaluation function • Features were chosen based on analysis of Othello • Edge Stability & Internal Stability • Current Mobility & Potential Mobility • Evaluation parameters were done manually

6. BILL (1990) • Partly pattern based, feature weights are learned • Edge Stability • Current Mobility & Potential Mobility • Sequence Penalty • Evaluation speed increased by using pre-computed tables • In comparison, BILL wins all games against IAGO, with 20% the thinking time

7. Logistello-1(1994) • Pattern values learned independently from sample data • Uses logistic regression to combine features • Current Mobility & Potential Mobility • Patterns

8. Logistello-1(1994) • Evaluation function is entirely table based • All evaluation parameters are learned from sample positions • Logistello uses selective search heuristic called ProbCut • Dominated computer Othello until 1996

9. Logistello-2(1997) • Joint learning of pattern values • Assigning pattern values independently neglected pattern correlations • Can assign arbitrary values to patterns whose meaning is not bound by limited human understanding of the problem • Strength increase from 1994 version is ten-fold

10. Other Important Improvements • Opening books • Saves time • Avoids falling into known strategic traps • Less chance of losing two games in the same way • End game search • Allows for optimal play near end

11. Takeshi Murakami vs. LogistelloMichael Buro, 1997 • Both humans and computers have improved playing Othello • Against imperfect human players it pays off to complicate endgame positions, not so with strong Othello programs

12. Human vs. Computer Takeshi Murakami Michael Buro and is program Logistello

13. Discovering Complex Othello Strategies…D. E. Moriarty & Risto Miikkulainen, 1997 • Found that experts search selective paths through pattern recognition • Most programs used deeper searches to be effective • Wanted a “human-like” approach

14. Neural Networks • Networks learned Othello without previous knowledge • No hand-coded rules or heuristics • Strategies evolved through play • No search mechanism • Goal was to discover strategies

15. Implementation • Neural networks relied on pattern recognition • Used marker-based scheme with genetic algorithms • Network architecture and weights evolve • Population of 50 networks • Initially evolved against random move maker

16. Results • Positional strategy against random mover after 100 generations

17. Results • Mobility strategy against searcher after 2000 generations

18. Articles • M. Buro, The Evolution of Strong Othello Programs, 2003 • M. Buro, Takeshi Murakami vs. Logistello, 1997 • D. E. Moriarty & R. Miikkulainen, Discovering Complex Othello Strategies Through Evolutionary Neural Networks, 1995

19. Websites • Michael Buro http://www.cs.ualberta.ca/~mburo/ • Neural Networks Research Group http://nn.cs.utexas.edu/ • Free online Othello game http://brittany.angloinfo.com/games/iago.asp

20. Questions ??