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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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