Author: Uri Blass
Date: 15:56:57 08/18/05
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On August 18, 2005 at 17:44:03, Robert Hyatt wrote: >On August 18, 2005 at 16:03:31, Vincent Lejeune wrote: > >>On August 18, 2005 at 14:09:08, Robert Hyatt wrote: >>... >>> The Sjeng game was simply something overlooked >>>months ago that was easy to fix. This game had a book problem, but even after >>>the g5, I wonder if Crafty could have played it better. I'm looking now... >> >>Could you give more informations about this "old bug", please ? > > >Yes. Somewhere way back in the 19's, I removed the last bit of "root >pre-processing" code. One of the pieces was a bit of code that initialized the >pawn piece/square table from one of three different sources, depending on >whether the games was in the opening, middle-game or endgame phases. Somehow I >removed the preprocessing piece, but never pre-initialized the piece square >table to slightly encourage pawn advances in general. As a result, there was >_zero_ incentive unless it was pushing a passed pawn, or making a passed pawn. >If you look at the Sjeng ending, it was a dead drawn position, but crafty just >sat back and let Sjeng advance the pawns until you reach one of those positions >where black can then make a passed pawn and it is closer to promotion than >white's resulting passer. After initializing (by hand) the pawn piece-square >table to values similar to 19.0, I replayed the game and Crafty varied so >significantly I decided to play a lot of test games to see if it was "better" or >"worse" before the changes. It was worse. :) So I left the changes in since >they had effectively been tested for several years prior to their unintentional >removal... > >Crafty version 20.0 is going to see the start of a major revision of the eval >code to get it cleaned up. Too much overlap, and interaction. For example, >blockading a passed pawn. I do it in one place, then give less of a bonus for a >rook behind a blockaded passer somewhere else, which is duplicated work that >could be avoided. Probably lots of unintended side-effects scattered around all >over so it is about time to re-do this and clean things up completely... If I understand you correctly you say that Crafty after the game against Sjeng is without the bug of not advancing pawns and probably better than Crafty before the game against Sjeng. Do you think that removing the last bit of the root pre-processing" code may be the reason that Crafty19.17 seems to be weaker than older versions? Uri
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