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1.1     ! root        1: This file contains a description of GNU's heuristics.
        !             2:    Copyright (C) 1986, 1987 Free Software Foundation, Inc.
        !             3: 
        !             4: This file is part of CHESS.
        !             5: 
        !             6: CHESS is distributed in the hope that it will be useful,
        !             7: but WITHOUT ANY WARRANTY.  No author or distributor
        !             8: accepts responsibility to anyone for the consequences of using it
        !             9: or for whether it serves any particular purpose or works at all,
        !            10: unless he says so in writing.  Refer to the CHESS General Public
        !            11: License for full details.
        !            12: 
        !            13: Everyone is granted permission to copy, modify and redistribute
        !            14: CHESS, but only under the conditions described in the
        !            15: CHESS General Public License.   A copy of this license is
        !            16: supposed to have been given to you along with CHESS so you
        !            17: can know your rights and responsibilities.  It should be in a
        !            18: file named COPYING.  Among other things, the copyright notice
        !            19: and this notice must be preserved on all copies.  */
        !            20: 
        !            21:  -- requested by main author
        !            22: Heuristic descriptions for CHESS.
        !            23: 
        !            24: Revision: 12-16-87
        !            25: 
        !            26: Copyright (c) 1987 by John Stanback
        !            27: 
        !            28:   Here is a brief description of the heuristics used in the positional 
        !            29:   evaluator of the GNU Chess program. Many heuristics are functions of the 
        !            30:   stage of the game which is based on the total non-pawn material remaining 
        !            31:   for both sides. 
        !            32:     
        !            33: 
        !            34: PAWNS
        !            35:     The material value of a pawn is 100 points. Isolated pawns get a 
        !            36:     penalty depending on which file they occupy: 
        !            37:        (12,14,16,20,20,16,14,12) for files (a..h).
        !            38:     Doubled pawns (which are not also isolated) get a penalty of 12 
        !            39:     points. Backward pawns (defined simply as not being defended by a 
        !            40:     pawn with the square in front also not defended by a a pawn) are 
        !            41:     penalized 6 points. A 4 point penalty is also invoked for each attack 
        !            42:     by the opponent to a backward pawn and for a backward pawn on a 
        !            43:     half-open file. Pawn Advancement in the centre is given a bonus of 
        !            44:     about 4 points per rank in the opening increasing to about 8 points 
        !            45:     per rank in the ending. Advancement on the edges is given a lower 
        !            46:     bonus. Pawns on the e and d files and on the 2nd rank are given a 10 
        !            47:     point penalty. An additional penalty of 15 points is invoked if these 
        !            48:     pawns are also blocked. Pawns within 2 squares of the king are given 
        !            49:     a 10 point bonus. Passed pawns are given a bonus for increasing rank 
        !            50:     which is a function of stage of the game and of whether the opponent 
        !            51:     blocks or attacks one or more squares in front of the pawn or if the 
        !            52:     opponents king is in the square of the pawn. This bonus ranges from 
        !            53:     about 15 points for a pawn on the second rank up to about 300 points 
        !            54:     for a passed pawn on the 7th rank which can't be stopped from 
        !            55:     queening. 
        !            56:               
        !            57: 
        !            58: KNIGHTS
        !            59:     The material value of a knight is 330 points. The main heuristic for 
        !            60:     knights is a bonus for proximity to the centre. This varies from 0 
        !            61:     points in the corners to 30 points in the centre. Knights are also 
        !            62:     given a bonus for being within 2 squares of each enemy piece. This 
        !            63:     bonus is a function of the stage of the game, equalling 4 points in 
        !            64:     the end game. A penalty of 1 point per square is given for distance 
        !            65:     from either king. A bonus of up to 8 points (depends on stage) is 
        !            66:     given for knights which can't be driven away by enemy pawns. 
        !            67: 
        !            68: 
        !            69: BISHOPS
        !            70:     The material value of a bishop is 330 points. Bishops are given a 
        !            71:     bonus as material falls off the board equalling 10 points in the end 
        !            72:     game. Bishops get a bonus for mobility and Xray mobility thru pieces 
        !            73:     but not pawns. This bonus ranges from -4 points for a totally blocked 
        !            74:     bishop up to 18 points for a bishop attacking 12 or more squares. 
        !            75:     Xray attacks on an enemy R,Q,K or any undefended piece are given an 8 
        !            76:     point bonus. Bishops are given a bonus of 14 points if they lie on 
        !            77:     the edge of the board up to 22 points if the lie in the centre. A 
        !            78:     bishop is given a bonus of up to 5 points for each attack to a square 
        !            79:     adjacent to the enemy king. 
        !            80: 
        !            81: 
        !            82: ROOKS
        !            83:     The material value of a rook is 520 points. Rook mobility is handled 
        !            84:     similiarly to bishops with a bonus of 0 points if blocked up to 20 
        !            85:     points if attacking 12 squares or more. A bonus of 8 points for Xray 
        !            86:     attacks is handled as it is for bishops. Rooks are given a bonus of 
        !            87:     10 points for occupying a file with no friendly pawns and a bonus of 
        !            88:     4 points if no enemy pawns lie on that file. After the opening Rooks 
        !            89:     are penalized slightly depending on "taxicab" distance to the enemy 
        !            90:     king. 
        !            91:   
        !            92: 
        !            93: QUEENS
        !            94:     The material value of a queen is 980 points. The only heuristic for a 
        !            95:     queen is that after the opening it is penalized slightly for 
        !            96:     "taxicab" distance to the enemy king. 
        !            97: 
        !            98: 
        !            99: KINGS
        !           100:     Kings are given a penalty for proximity to the centre in the opening 
        !           101:     and a bonus for proximity to the centre in the endgame. The penalty 
        !           102:     is about 24 points for being in the centre in the opening with a 
        !           103:     bonus of about 36 points for being in the centre in the endgame. 
        !           104:     Kings are penalized for lying on an open or half-open file or if the 
        !           105:     adjacent file closest to the corner is open or half-open. This 
        !           106:     penalty is up to 23 points in the opening and goes to zero in the end 
        !           107:     game. The King is penalized up to 8 points if there are no pawns 
        !           108:     immediately adjacent. A penalty is invoked depending on the number of 
        !           109:     "safe" checks available by the opponent. This penalty ranges from 6 
        !           110:     points for one such check to 50 points for 4 or more. Depending on 
        !           111:     game stage, Kings are given up to 10 points for castling and a 
        !           112:     penalty of up to 40 points for moving before castling. 
        !           113:   
        !           114: 
        !           115: SPECIAL
        !           116:     If more than one piece is "hung" (attacked and not defended or 
        !           117:     attacked by an enemy piece of lower value) an extra penalty of 10 
        !           118:     points is invoked for that side and the search may be extended one 
        !           119:     ply. Pinned or trapped pieces are treated similarly. A special mating 
        !           120:     routine is used if one side has only a king and the other has mating 
        !           121:     material. 
        !           122: 

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