Computer shogi

Computer shogi is a field of artificial intelligence concerned with the creation of computer programs which can play shogi. The research and development of shogi software has been carried out mainly by freelance programmers, university research groups and private companies. By 2017, the strongest programs were outperforming the strongest human players. Shogi has the distinctive feature of reusing captured pieces. Therefore, shogi has a higher branching factor than other chess variants. The computer has more positions to examine because each piece in hand can be dropped on many squares. This gives shogi the highest number of legal positions and the highest number of possible games of all the popular chess variants. The higher numbers for shogi mean it is harder to reach the highest levels of play. The number of legal positions and the number of possible games are two measures of shogi's game complexity. The complexity of Go can be found at Go and mathematics. More information on the complexity of Chess can be found at Shannon number. The primary components of a computer shogi program are the opening book, the search algorithm and the endgame. The "opening book" helps put the program in a good position and saves time. Shogi professionals, however, do not always follow an opening sequence as in chess, but make different moves to create good formation of pieces. The "search algorithm" looks ahead more deeply in a sequence of moves and allows the program to better evaluate a move. The search is harder in shogi than in chess because of the larger number of possible moves. A program will stop searching when it reaches a stable position. The problem is many positions are unstable because of the drop move. Finally, the "endgame" starts when the king is attacked and ends when the game is won. In chess, there are fewer pieces which leads to perfect play by endgame databases; However, pieces can be dropped in shogi so there are no endgame databases. A tsumeshogi solver is used to quickly find mating moves.