Author: Alvaro Jose Povoa Cardoso
Date: 10:04:50 11/21/04
Hi, below there is a quote of my previous question on this matter and your answer. My new question is if we avoid storing drawn by repetition positions in the hash table would we avoid the problem of getting "draws in 90 plies, even though you can't search beyond (say) 64 plies" like you said? If so what kind of mechanism would we have to implement to detect these cases? Maybe a special bit set on the score variable? Best regards, Alvaro Cardoso ----------------------------------------------------------------- My question: >>I was wondering if it is correct to assign a zero score to a position that is >>a draw by 3 fold repetition. >>What I mean is that if for example white is ahead in material and black is >>fighting desperately for a draw, black will try to reach that drawn position >>as quick as possible while white will try to postpone that position as much as >>it can. >>It's a sort of distance to mate but in this case it is a distance to draw by >>repetition. >>Does this make any sense to you? >>I would appreciate your comments. >> >>Best regards, >>Alvaro Cardoso Your answer: >Forget that idea. We did it in Cray Blitz, and it causes _massive_ problems. >IE in CB, we blocked off the scores from 0.000 to 0.100 to be draws only. We >did this by the simple trick at the end of Evaluate() where we just did the > >if (score >= 0) score += 100; > >100 was 100 millipawns in CB. > >The problem is the path. You don't store the path. You will be amazed that >once you do the above, and then try the thing we did (see "The Cray Blitz draw >heuristic" in the JICCA) you will get draws in 90 plies, even though you can't >search beyond (say) 64 plies. Mates work fine because you search to a stopping >point. But draws do not, and the hash table grafts scores from one part of the >tree to another producing some pretty bizarre scores. In fact, you can get >scores that are outside the draw window if you are not careful, which _really_ >will wreck your search. > >Been there.
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