123 lines
5.9 KiB
Plaintext
123 lines
5.9 KiB
Plaintext
This file contains a description of GNU's heuristics.
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Copyright (C) 1986, 1987 Free Software Foundation, Inc.
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This file is part of CHESS.
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CHESS is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY. No author or distributor
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accepts responsibility to anyone for the consequences of using it
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or for whether it serves any particular purpose or works at all,
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unless he says so in writing. Refer to the CHESS General Public
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License for full details.
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Everyone is granted permission to copy, modify and redistribute
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CHESS, but only under the conditions described in the
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CHESS General Public License. A copy of this license is
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supposed to have been given to you along with CHESS so you
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can know your rights and responsibilities. It should be in a
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file named COPYING. Among other things, the copyright notice
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and this notice must be preserved on all copies. */
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-- requested by main author
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Heuristic descriptions for CHESS.
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Revision: 12-16-87
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Copyright (c) 1987 by John Stanback
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Here is a brief description of the heuristics used in the positional
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evaluator of the GNU Chess program. Many heuristics are functions of the
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stage of the game which is based on the total non-pawn material remaining
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for both sides.
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PAWNS
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The material value of a pawn is 100 points. Isolated pawns get a
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penalty depending on which file they occupy:
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(12,14,16,20,20,16,14,12) for files (a..h).
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Doubled pawns (which are not also isolated) get a penalty of 12
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points. Backward pawns (defined simply as not being defended by a
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pawn with the square in front also not defended by a a pawn) are
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penalized 6 points. A 4 point penalty is also invoked for each attack
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by the opponent to a backward pawn and for a backward pawn on a
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half-open file. Pawn Advancement in the centre is given a bonus of
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about 4 points per rank in the opening increasing to about 8 points
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per rank in the ending. Advancement on the edges is given a lower
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bonus. Pawns on the e and d files and on the 2nd rank are given a 10
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point penalty. An additional penalty of 15 points is invoked if these
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pawns are also blocked. Pawns within 2 squares of the king are given
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a 10 point bonus. Passed pawns are given a bonus for increasing rank
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which is a function of stage of the game and of whether the opponent
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blocks or attacks one or more squares in front of the pawn or if the
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opponents king is in the square of the pawn. This bonus ranges from
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about 15 points for a pawn on the second rank up to about 300 points
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for a passed pawn on the 7th rank which can't be stopped from
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queening.
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KNIGHTS
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The material value of a knight is 330 points. The main heuristic for
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knights is a bonus for proximity to the centre. This varies from 0
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points in the corners to 30 points in the centre. Knights are also
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given a bonus for being within 2 squares of each enemy piece. This
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bonus is a function of the stage of the game, equalling 4 points in
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the end game. A penalty of 1 point per square is given for distance
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from either king. A bonus of up to 8 points (depends on stage) is
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given for knights which can't be driven away by enemy pawns.
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BISHOPS
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The material value of a bishop is 330 points. Bishops are given a
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bonus as material falls off the board equalling 10 points in the end
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game. Bishops get a bonus for mobility and Xray mobility thru pieces
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but not pawns. This bonus ranges from -4 points for a totally blocked
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bishop up to 18 points for a bishop attacking 12 or more squares.
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Xray attacks on an enemy R,Q,K or any undefended piece are given an 8
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point bonus. Bishops are given a bonus of 14 points if they lie on
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the edge of the board up to 22 points if the lie in the centre. A
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bishop is given a bonus of up to 5 points for each attack to a square
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adjacent to the enemy king.
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ROOKS
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The material value of a rook is 520 points. Rook mobility is handled
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similiarly to bishops with a bonus of 0 points if blocked up to 20
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points if attacking 12 squares or more. A bonus of 8 points for Xray
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attacks is handled as it is for bishops. Rooks are given a bonus of
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10 points for occupying a file with no friendly pawns and a bonus of
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4 points if no enemy pawns lie on that file. After the opening Rooks
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are penalized slightly depending on "taxicab" distance to the enemy
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king.
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QUEENS
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The material value of a queen is 980 points. The only heuristic for a
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queen is that after the opening it is penalized slightly for
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"taxicab" distance to the enemy king.
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KINGS
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Kings are given a penalty for proximity to the centre in the opening
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and a bonus for proximity to the centre in the endgame. The penalty
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is about 24 points for being in the centre in the opening with a
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bonus of about 36 points for being in the centre in the endgame.
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Kings are penalized for lying on an open or half-open file or if the
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adjacent file closest to the corner is open or half-open. This
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penalty is up to 23 points in the opening and goes to zero in the end
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game. The King is penalized up to 8 points if there are no pawns
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immediately adjacent. A penalty is invoked depending on the number of
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"safe" checks available by the opponent. This penalty ranges from 6
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points for one such check to 50 points for 4 or more. Depending on
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game stage, Kings are given up to 10 points for castling and a
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penalty of up to 40 points for moving before castling.
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SPECIAL
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If more than one piece is "hung" (attacked and not defended or
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attacked by an enemy piece of lower value) an extra penalty of 10
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points is invoked for that side and the search may be extended one
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ply. Pinned or trapped pieces are treated similarly. A special mating
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routine is used if one side has only a king and the other has mating
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material.
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