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Improving Strategic Play in Shogi by Using Move Sequence Trees

Improving Strategic Play in Shogi by Using Move Sequence Trees. Reijer Grimbergen Department of Informatics Yamagata University. Outline. Opening play in Shogi The problems of hill-climbing Move sequence trees Extracting move sequences Using move sequence trees Preliminary results

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Improving Strategic Play in Shogi by Using Move Sequence Trees

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  1. Improving Strategic Play in Shogi by Using Move Sequence Trees Reijer Grimbergen Department of Informatics Yamagata University GPW2007

  2. Outline • Opening play in Shogi • The problems of hill-climbing • Move sequence trees • Extracting move sequences • Using move sequence trees • Preliminary results • Conclusions and future work GPW2007

  3. Opening play in shogi • The weak point of shogi programs is opening play • “Endgame: 6-dan, opening: 1-kyu” • Shogi programs cannot handle long term strategy • Strategic knowledge cannot be obtained by search alone • Example: building a castle formation can take more than 10 moves by one player GPW2007

  4. Opening play in shogi 玉（美濃囲い） 金（美濃囲い） 銀（美濃囲い） GPW2007

  5. The problems of hill-climbing 1）　4八玉　　3八玉　　2八玉　　3八銀　　5八金(69) 2）　3八銀　　4八玉　　5八金(69)3九玉　　2八玉 3）　5八金(69)3八銀　　4八玉　　3九玉　　2八玉 　　　　　　　　　　　　　　　　： 　　　　　　　　　　　　　　　　： GPW2007

  6. The problems of hill-climbing 6七金(58) 6八金(58) 6七金(68) GPW2007

  7. Move sequence trees • Information about move order is needed to solve the problems of hill-climbing • Move sequence trees • For each opening strategy, collect information about common move orders • Save this data in move sequence trees • Use move sequence trees to guide the search GPW2007

  8. Extracting move sequences • Move sequence extraction • Collect games with a with a specific opening strategy • Collecting move frequency data • Generate a move sequence tree GPW2007

  9. Collecting games • Find all games with a finished castle • In the Shogi Club24 database (240,000 games) • Personal professional game database (5,000 games) • Yagura • Sente: 2548 games (SC24: 1815, Pro: 733) • Gote: 2036 games (SC24: 1520, Pro: 516) GPW2007

  10. Collecting move frequency data • Yagura for sente • 1288 different moves in the first 50 moves of the game • Only 153 moves were played in 1% of the games or more GPW2007

  11. 976 876 ２六歩(27) ２六歩(27) 360 6 549 ６八銀(79) ４八銀(39) ６六歩(67) 85 5 ４八銀(39) ５八金(49) Same position 80 ７八金(69) 517 2813 942 ６六歩(67)** ６八銀(79) Start ７六歩(77) 315 58 ７七銀(68) ７七角(88) 5 32 ６六歩(67) 7 ７八銀(79) ５六歩(57) 27 4 ８八銀(同角) ５六歩(57) 5 15 ４八銀(39) １六歩(17) 3 14 3 ７八金(69) ５六歩(57) ２六歩(27) 12 3 ２二角成(88) 2 ６八玉(59) ７八金(69) 9 ５八金(49) 2 2 5 ５八飛(28) ５八飛(28) ６八玉(59) 2 1 ３六歩(37) １六歩(17) GPW2007

  12. Using move sequence trees • Step 1: Select a move sequence tree • Not all move sequence trees can be loaded at the same time • Use move frequencies to find the best match • Step 2: Access the move sequence tree during the search • Use a pointer to the move sequence tree • Award an evaluation bonus for each move that follows the move sequence tree GPW2007

  13. Preliminary results GPW2007

  14. Conclusions and future work • Conclusions • Using move sequence trees may be an improvement of hill-climbing methods • It seems unlikely that move sequence trees are the best solution • Future work • Generate move sequence trees for all opening strategies • Bonus values should be based on move frequency • Move sequence tree selection should be based on partial hashcodes GPW2007

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