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Board Maps and Hill-Climbing for Opening and Middle Game Play in Shogi. Reijer Grimbergen (Saga University) Jeff Rollason (Oxford Softworks). Overview. Opening books in games Problems of using a standard opening book in shogi Board maps for opening and middle game play in shogi

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board maps and hill climbing for opening and middle game play in shogi

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

overview
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

opening books in games
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

problems of using a standard opening book in shogi
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

problems of using a standard opening book in shogi1
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

board maps for opening and middle game play in shogi
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

board maps for opening and middle game play in shogi1
Board maps for opening and middle game play in shogi
  • Piece formations
  • Total
    • 35 castle formations
    • 20 assault formations

Computers and Games 2002

board maps for opening and middle game play in shogi2
Board maps for opening and middle game play in shogi
  • Individual board maps
    • Example: Mino castle

Computers and Games 2002

board maps for opening and middle game play in shogi3
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

board maps for opening and middle game play in shogi4
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

use the maps to guide opening and middle game play

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

use the maps to guide opening and middle game play1
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

extensions of the basic method
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

results
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

results1
Results

Computers and Games 2002

results2
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

related work
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

conclusions and future work
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