Author: Robert Hyatt
Date: 14:44:03 08/18/05
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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...
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