Author: Robert Hyatt
Date: 19:45:16 12/03/02
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On December 03, 2002 at 18:59:20, Jon Dart wrote: >On December 03, 2002 at 17:16:58, Robert Hyatt wrote: > >> >>the idea is to do anything you can to exclude moves. Because below each move >>you search, you grow a tree, and that is expensive. If alpha is 0.00, and >>the current material score is -15.0, then capturing a pawn is not going to >>help, and avoiding that capture avoids the tree below it. > >I've noticed that Crafty uses the material value as a basis for calculating >futilty. In other words, if material + SEE gain + safety margin < alpha, you cut >the move (I do something similar at present). > >What Mike is suggesting is to use the total position eval, which is also >something I've experimented with. So: if eval + capture + SEE gain + safety >margin < alpha, you cut. If you have large positional scores, this is possibly >safer (the "safety margin" in Crafty is only 1 pawn). If you follow the logic carefully, this is also what crafty is doing. At the top of Quiesce() I grab the positional (stand-pat) score, and if this is > alpha, then I set alpha to that value. All the pruning is then based off of this positional (material+positional returned by Evaluate()) score plus the capture gain, plus a fudge as removing a piece could increase the score but probably not by a lot... > >--Jon
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