Author: Mike Byrne
Date: 08:15:42 04/17/05
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On April 17, 2005 at 04:41:14, John J. J. Smith wrote: >On April 17, 2005 at 00:20:21, Mike Byrne wrote: > >>On April 16, 2005 at 22:13:45, John J. J. Smith wrote: >> >>>[d]8/8/8/2p5/1pp5/brpp4/qpprpK1P/1nkbn3 w - - 0 1 >>> >>>This seems to be a difficult problem for most engines. The key move is 2.h3. >>>2.h4 only leads to a draw >> >>Added a little code to Crafty handle the case where the one side has only one >>piece to disable null move. >> >What exactly did you do? Crafty 19.19 (Chessbase version) can't solve this. Nor >can Fritz and Junior. The position is unique and is a null move killer. Black has_ALL_of_its_pieces - but can just shuffle the Q around. White has one pawn but can change the tempo by moving the pawn 1 or two squares. Any program that solves this either does not have null move or turns it off for this position. You can have Crafty solve this by turning null move off manually -- all the line below without the quote to your crafty.rc file "sel 0 0" (note: if you leave this in crafty.rc for regular game play - crafty will play weaker. It is a good tool to use see if a problem why a position is not solved to see if the search is being impacted by null move. The normal setting is "sel 2 3") But what I did was added code that says if one side has just one piece , do_null=0 and have it skip the null move code in search.c if do_null==0. I can see why an author would not bother even considering changing code for this oddball position. Most modern programs do use null move of some sort, null move does allow programs to play stronger in most positions. Most program do turn off null move with very few pieces on the board. This is the extreme case where the potentially winning side has just one piece and the losing side still has ALL of its pieces. The code change I made has little practicality in real chess play as null move is usually inactivated with just a few pieces on the board anyway and that covers most situations which occur in a real game where one side has one piece. Best, Michael
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