Author: Harald Lüßen
Date: 01:50:05 01/14/06
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On January 14, 2006 at 00:15:25, Robert Hyatt wrote: >On January 13, 2006 at 18:38:35, Branislav Bezak wrote: > >> >>I struggle to prevent my opponent to draw by repetition when I’m using best move >>stored in entry in transposition table. >> >>At the beginning of AB function, I check the table, find a nice fat score and >>make the best move stored. My opponent makes his move and it's a draw by >>repetition. So, I added a code to check all opponent’s possible responses to my >>stored best move to see if they are not draw. In that case, I don't use the best >>move from hash table but force the full search to pick some other move that will >>not allow the opponent to draw. But there are cases where I still cannot prevent >>the draw because it is already too late and no matter what I do, my opponent’s >>next move is a draw. >> >>What's the best way how to deal with this situation? >> >>Thanks > > >I don't understand the question. You just use the "best move" as the first move >to search, but you _still_ search it. And you should pick up the repetition at >the next ply easily enough... You don't just take the best move and say "i'll >play that and not search any deeper"... I believe I do this right in my engine but I may have introduced a new similar bug in the last few weeks. Consider this situation: alpha = -20, beta = 20, depth = 10, Hash: value = 100, depth = 12, move = ... May I return from this position because hash value > beta? The hash move and the opponent's response may lead to an immediate repetition draw. I play this line hopefully winning a pawn and game over. Do I have to forbid hash value cutoffs? Do I have to restrict hash value cutoffs to deeper plies? Do I have to restrict hash value cutoffs to beta < value < 0? Do I have to check my move and its pv through the hash table and look for repetition draws (as Branislav does)? Does this depend on the recognized number of repetitions (2nd or 3rd) in the search? Do I have to store a repetition flag in the hash entry? When? How does that help in this situation? There could be another path to the current position, or not? How to react to such a flag? Harald
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