Author: Brian Richardson
Date: 10:08:31 01/25/01
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On January 25, 2001 at 11:07:53, Robert Hyatt wrote: >On January 25, 2001 at 09:42:16, Brian Richardson wrote: > >>On January 24, 2001 at 23:39:12, Robert Hyatt wrote: >> >>>push passed pawns is an extension that is triggered if a passed pawn is pushed >>>to the 7th rank only. >>>pushpp >>>0.00 sum of times(squared)=29373 >>>0.25 sum of times(squared)=29385 >>>0.50 sum of times(squared)=29336 >>>0.75 sum of times(squared)=29360 >>>1.00 sum of times(squared)=29375 >>>pushing a passed pawn had hardly any effect, but that might be a >>>result of the test suite rather than a useless extension. The default >>>value for this is also .75 >>> >>> >> >>Doesn't Crafty advance pawns in the evaluation anyway (until blocked or >>captured, I have not studied the code for some time), and then do its >>sophisticated passed pawn eval? This might account for the negligible extension >>effect. Just a thought. >>Brian > > >No, although if a pawn _is_ passed, the eval will understand if it is >unstoppable when the opponent has no pieces except a king that is too >far away. However it seems (to me) that pushpp is fairly ineffective... >and that recapture is a lemon completely... Thanks for the clarification. However, I still think the sophistication of Crafty's passed pawn evaluation (eg "knowing" if the pawn can be stopped or not) is what minimizes value of a "simple" generic search one ply extension, since this eval is the equivalent of looking many "plys" ahead. Programs lacking this advanced eval function may indeed benefit from an extension, although certainly not as much.
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