![]() ![]() This means those positions do not need to be searched again. To go through all positions from all games in the game database and determine the best move not played in any database game, transposition tables are used to record positions that have been previously searched. All strong programs use opening books and update their books automatically after each game. Opening books aid computer programs by giving common openings that are considered good ways to counter poor openings. The most common choice to predict the final disc difference uses a weighted disk difference measure where the winning side gets a bonus corresponding to the number of disks. The process of determining values for all configurations is done by taking a large database of games played between strong players and calculating statistics for each configuration in each game stage from all the games. Mobility maximization and frontier minimization can be broken down into local configurations which can be added together the usual implementation is to evaluate each row, column, diagonal and corner configuration separately and add together the values, lots of different patterns have to be evaluated. Most programs have knowledge of edge and corner configurations and try to minimize the number of disks during the early midgame, another strategy used by human players. These measures can be found very quickly, and they significantly increase playing strength. Player mobility and opponent mobility are calculated, and player potential mobility and opponent potential mobility are calculated as well. Most human players strive to maximize mobility (number of moves available) and minimize frontier disks (disks adjacent to empty squares). corners are more important in the opening and early midgame than in the endgame. A more sophisticated approach is to have different values for each position during the different stages of the game e.g. ![]() Disregarding symmetries, there are 10 different positions on a board, and each of these is given a value for each of the three possibilities: black disk, white disk and empty. Disk-square tablesĭifferent squares have different values - corners are good and the squares next to corners are bad. ![]() There are three different paradigms for creating evaluation functions. Several experiments have been made with the game Othello, like ABDADA or APHID On recent programs, the YBWC seems the preferred approach. To speed up the search on machines with multiple processors or cores, a "parallel search" may be implemented. Several heuristics are also used to reduce the size of the searched tree: good move ordering, transposition table and selective Search. This method takes advantage of the fact that every other level in the tree will maximize and every other level will minimize. The alphabeta algorithm is a method for speeding up the Minimax searching routine by pruning off cases that will not be used anyway. These are based on Alpha-beta pruning, Negascout, MTD-f, NegaC*. This search continues until a certain maximum search depth or the program determines that a final "leaf" position has been reached.Ī naive implementation of this approach, known as Minimax or Negamax, can only search to a small depth in a practical amount of time, so various methods have been devised to greatly increase the speed of the search for good moves. In theory, they examine all positions / nodes, where each move by one player is called a "ply". Search techniquesĬomputer Othello programs search for any possible legal moves using a game tree. This is because although the consequences of moves are predictable for both computers and humans, computers are better at envisaging them. These programs, when run on any up-to-date computer, can play games in which the best human players are easily defeated. There are many Othello programs such as NTest, Saio, Edax, Cassio, Pointy Stone, Herakles, WZebra, and Logistello that can be downloaded from the Internet for free. ![]() Home :: Reversi Computer Othello Computer OthelloĬomputer Othello refers to computer architecture encompassing computer hardware and computer software capable of playing the game of Othello. ![]()
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