我正在尝试开发一个简单的国际象棋引擎,但我在其性能方面遇到了困难。我已经通过 alpha-beta 修剪和迭代加深(没有任何额外的启发式)实现了 Negamax,但是我无法获得超过 3-4 层的合理搜索时间。以下是我的程序从游戏开始时的日志的摘录:
2013-05-11 18:22:06,835 [9] INFO CoevolutionaryChess.Engine.MoveSearchers.NegamaxMoveSearcher [(null)] - Searching at depth 1
2013-05-11 18:22:06,835 [9] DEBUG CoevolutionaryChess.Engine.MoveSearchers.NegamaxMoveSearcher [(null)] - Leaves searched: 28
2013-05-11 18:22:06,835 [9] DEBUG CoevolutionaryChess.Engine.MoveSearchers.NegamaxMoveSearcher [(null)] - Nodes searched: 28
2013-05-11 18:22:06,835 [9] DEBUG CoevolutionaryChess.Engine.MoveSearchers.NegamaxMoveSearcher [(null)] - Found PV: A4->A6
2013-05-11 18:22:06,835 [9] INFO CoevolutionaryChess.Engine.MoveSearchers.NegamaxMoveSearcher [(null)] - Searching at depth 2
2013-05-11 18:22:06,897 [9] DEBUG CoevolutionaryChess.Engine.MoveSearchers.NegamaxMoveSearcher [(null)] - Leaves searched: 90
2013-05-11 18:22:06,897 [9] DEBUG CoevolutionaryChess.Engine.MoveSearchers.NegamaxMoveSearcher [(null)] - Nodes searched: 118
2013-05-11 18:22:06,897 [9] DEBUG CoevolutionaryChess.Engine.MoveSearchers.NegamaxMoveSearcher [(null)] - Found PV: A2->A3 B7->B6
2013-05-11 18:22:06,897 [9] INFO CoevolutionaryChess.Engine.MoveSearchers.NegamaxMoveSearcher [(null)] - Searching at depth 3
2013-05-11 18:22:08,005 [9] DEBUG CoevolutionaryChess.Engine.MoveSearchers.NegamaxMoveSearcher [(null)] - Leaves searched: 6027
2013-05-11 18:22:08,005 [9] DEBUG CoevolutionaryChess.Engine.MoveSearchers.NegamaxMoveSearcher [(null)] - Nodes searched: 6414
2013-05-11 18:22:08,005 [9] DEBUG CoevolutionaryChess.Engine.MoveSearchers.NegamaxMoveSearcher [(null)] - Found PV: A2->A3 A6->B8 A4->A7
2013-05-11 18:22:08,005 [9] INFO CoevolutionaryChess.Engine.MoveSearchers.NegamaxMoveSearcher [(null)] - Searching at depth 4
2013-05-11 18:22:10,485 [9] DEBUG CoevolutionaryChess.Engine.MoveSearchers.NegamaxMoveSearcher [(null)] - Leaves searched: 5629
2013-05-11 18:22:10,485 [9] DEBUG CoevolutionaryChess.Engine.MoveSearchers.NegamaxMoveSearcher [(null)] - Nodes searched: 6880
2013-05-11 18:22:10,485 [9] DEBUG CoevolutionaryChess.Engine.MoveSearchers.NegamaxMoveSearcher [(null)] - Found PV: D2->D4 A6->B8 C4->C5 A7->A6
2013-05-11 18:22:10,485 [9] INFO CoevolutionaryChess.Engine.MoveSearchers.NegamaxMoveSearcher [(null)] - Searching at depth 5
2013-05-11 18:22:34,353 [9] DEBUG CoevolutionaryChess.Engine.MoveSearchers.NegamaxMoveSearcher [(null)] - Leaves searched: 120758
2013-05-11 18:22:34,353 [9] DEBUG CoevolutionaryChess.Engine.MoveSearchers.NegamaxMoveSearcher [(null)] - Nodes searched: 129538
2013-05-11 18:22:34,353 [9] DEBUG CoevolutionaryChess.Engine.MoveSearchers.NegamaxMoveSearcher [(null)] - Found PV: D2->D4 A6->B8 C4->C5 A7->A6 A4->A6
它显示分支因子约为 10。我读到,通过正确的移动顺序,我应该得到 6 左右的值,所以我怀疑我的顺序是错误的。目前它的工作方式如下:
- 游戏树节点有一个其子节点的链表;最初,捕获和晋升被置于安静的行动之前
- 在搜索过程中,增加 alpha 或导致截止的子项将放置在列表的开头
- 下一次迭代深化PV应该首先搜索
这是排序动作的正确方法吗?我得到的分支因子是预期的吗?目前我正在使用一个简单的静态评估函数,仅考虑职位的实质性差异 - 这是否是截止率低的原因(如果也考虑数字的流动性,我会得到类似的结果)?诸如空着减少或杀手启发式等技术是否会有显着帮助(不是 10-15%,而是一个数量级)?我不期望我的引擎很强,但我希望分支因子约为 6。