Author: Martin Schubert
Date: 13:59:15 05/13/01
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On May 13, 2001 at 12:08:52, Uri Blass wrote: >On May 13, 2001 at 10:07:27, Robert Hyatt wrote: > >>On May 13, 2001 at 03:50:15, Gian-Carlo Pascutto wrote: >> >>>...when it could happen to you. >>> >>>On ICC my program reached the following position: >>> >>>[D]2k2r2/2P3R1/1P6/P7/8/1K6/8/8 w - - 0 56 >>> >>>Convinced it was winning, it now played a6?? >>>after which black draws easily. >>> >>>I remember having seen this theme before in problems, >>>but not in a real game. Ouch! >>> >>>Most other programs don't seem to have a clue about >>>this position either, though :) >>> >>>-- >>>GCP >> >>It's a null-move killer because it is based on zugzwang problems. White is >>up material + whatever bonuses it gets for three connected passers, which is >>quite a bit normally. Which means that any null move done will think white is >>simply winning. > >Yace is a null mover and it has no problem to see that moves like Kb4 are better >than a6. > >You do not need to see that a6 is a draw in order to avoid it and you only need >to see that other moves are better. > > The sequence of checks to reach the draw is also quite long >>which aggravates things... > >The main problem of a lot of chess programs is their evaluation, > >They can see a lot of checks and after the checks capturing the rook and believe >that white is a rook and 3 pawns up because they do not see the stalemate. > >Programs evaluate the position as more than +9 for white and it is ridicilous(I >guess that the +9 is evaluation of stalemate positions). >Yace is more inteligent and evaluates a6 only as +5 for white and it is enough >for it to avoid a6. > >It will be interesting to see if Crafty can avoid the mistake if you add the >following if in your evaluation function: > >If the side to move has only a king then if the side to move is in stalemate >then return 0. > >The side to move has only a king is only a private case and you may add more >cases but the price is being slower in other positions. > >Uri Are you sure that some programs have a stalemate evaluation different from 0? Stalemate is draw, so why evaluate it different from 0? Martin
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