Board Maps and Hill-Climbing for Opening and Middle Game Play in Shogi

1. Board Maps and Hill-Climbing for Opening and Middle Game Play in Shogi Reijer Grimbergen (Saga University) Jeff Rollason (Oxford Softworks) Computers and Games 2002

2. Overview • Opening books in games • Problems of using a standard opening book in shogi • Board maps for opening and middle game play in shogi • Use the maps to guide opening and middle game play • Extensions of the basic method • Results • Related work • Conclusions and future work Computers and Games 2002

3. Opening books in games • In most two-player perfect information games the initial position is known • Use an opening bookto guide play • Out of book: the current position is not in the opening book • Examples • The chess programs Belle and Deep Blue • The checkers program Chinook • The Othello program Logistello Computers and Games 2002

4. Problems of using a standard opening book in shogi • Differences between chess and shogi • Different board size • Different pieces • Re-use of captured pieces • Less mobility for each individual piece • Different castling rules • Different promotion rules • How do the differences affect opening play? • Bigger board and less mobility make it less likely that pieces come into contact early • It takes a number of moves to build a strong castle formation, so this is a high priority in the opening Computers and Games 2002

5. Problems of using a standard opening book in shogi • Test • Standard opening book with 110,000 positions • 25 games each against AI Shogi, Kakinoki Shogi, Todai Shogi and Kanazawa Shogi • Results • Out of book within 5 moves in 32 games, within 10 moves in 71 games • Average: out of book in 8.5 moves Computers and Games 2002

6. Board maps for opening and middle game play in shogi • Castle and assault formations in shogi • Build a castle with three generals • Use the fourth general, bishop, rook and knight for assault • Formations depend on the position of the opponent rook: Ibisha (Static Rook) or Furibisha (Ranging Rook) • Use piece maps and hill-climbing to build castle and assault formations • Piece formations • Individual pieces • Square values Computers and Games 2002

7. Board maps for opening and middle game play in shogi • Piece formations • Total • 35 castle formations • 20 assault formations Computers and Games 2002

8. Board maps for opening and middle game play in shogi • Individual board maps • Example: Mino castle Computers and Games 2002

9. Board maps for opening and middle game play in shogi • Board maps for individual pieces • Example: Mino king Hill-climbing • K5i  K4h  K3h  K2h • K5i  K4h  K3i  K2h • Both paths have square values {-5, 2, 8, 14} Computers and Games 2002

10. Board maps for opening and middle game play in shogi • Constructing a sequence of moves • Example: Combining mino king with silver (left) and gold (right) Computers and Games 2002

11. Step 2 Use the piece formation table to get the assault formations Step 3 Use hill-climbing to guide the search towards improving the castle and assault formations Use the maps to guide opening and middle game play Step 1 Select the castle formation that resembles the current formation most Computers and Games 2002

12. Use the maps to guide opening and middle game play • Other ways the maps can be useful • Playing moves in the correct order • Add bonus values to moves • Bonus values are relative to the improvement of the square value and to the search depth • Opening book guidance • Only follow the opening book if the maps agree with the opening book suggestion • Establishing the difference between opening and middle game • Use thresholds on total castle value Computers and Games 2002

13. Extensions of the basic method • Swapping rules • The selection process needs extra shogi knowledge IF Castle = Yagura AND Bishop exchanged THEN Castle = Kakugawari • Especially important for assaults as there can be more than one assault on a castle • Scaling of formation values • Importance of piece formations relative to the game stage • Helps to make a decision when there is only a subtle difference between formations IF Castle = Anaguma AND Corner lance on initial square THEN Decrease castle value by 20% • Multiple castles • Keep multiple castle formations with similar total values • Allows to change between castles in the search • Note:Except for game stage scaling, the extensions are only used in the opening Computers and Games 2002

14. Results • Self-play experiment • Three versions of the shogi program SPEAR • AllMaps:Both castle maps and assault maps • CasMaps: Only castle maps • NoMaps: No maps • Follow the opening book for 5, 10, 20, 30 and 40 moves • Play the position twice when the program gets out of book • Fifty games with 25 minutes per side per game Computers and Games 2002

15. Results Computers and Games 2002

16. Results • Maps and opening book • With almost no support from the opening book, the program benefits significantly from the use of castle and assault maps • When the opening book is used for 30 or 40 moves, the maps do not give any improvement in playing strength • Combine maps with a standard opening book • Using the opening book for 5 moves gives worse results than using the opening book for 10 moves • Castle maps and assault maps • Using both castle maps and assault maps is better than using only castle maps Computers and Games 2002

17. Related work • The otoshiana method (Yamashita) • Also uses hill-climbing to build castle formations • How many formations? • No assault formations? • Similarity measure (Kotani) • Give an evaluation bonus to moves that have been played in similar positions • Extended opening book (Deep Blue) • Direct the search to moves played often by experts Computers and Games 2002

18. Conclusions and future work • Conclusions • Board maps for castle and assault formations can significantly improve the playing strength of a shogi program • Using both castle and assault maps gives better results than using only castle maps • Future work • Measure strong opening play objectively by playing other programs or use the opinion of an expert • Separate tests to establish the importance of the extensions of the basic method • Automatic learning of board maps • Use the maps not only for formations, but also for other positional elements of piece evaluation Computers and Games 2002