Author: Robert Hyatt
Date: 12:32:53 11/15/04
Go up one level in this thread
On November 15, 2004 at 15:03:23, Alvaro Jose Povoa Cardoso wrote: >On November 15, 2004 at 14:56:10, Anthony Cozzie wrote: > >>On November 15, 2004 at 14:43:59, Alvaro Jose Povoa Cardoso wrote: >> >>>On November 15, 2004 at 12:13:40, David Dahlem wrote: >>> >>>>On November 15, 2004 at 11:46:13, Alvaro Jose Povoa Cardoso wrote: >>>> >>>>>I was wondering if it is correct to assign a zero score to a position that is a >>>>>draw by 3 fold repetition. >>>> >>>>That's the way i do it. Otherwise, how else could any engine decide, based on >>>>the evaluation score, whether to go for repetition or to avoid repetition? >>>> >>>>Regards >>>>Dave >>> >>> >>>What I find strange is why crafty doesn't do it. >>>Comments Dr. Robert Hyatt? >>> >>>Alvaro >>> >>> >>> >>>> >>>>>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. >>>>> >>>>>Brest regards, >>>>>Alvaro Cardoso >> >>Crafty does it (0.01 -> black forces draw in position good for white, -0.01 >>white forces draw in position good for black). I really should implement this >>in Zappa. >> >>anthony > >Yes, but it is not the same thing. It doesn't do it in the 'distance to mate' >way. It doesn't care how far/near that draw position is in the tree, so it will >not make any progress torwards it. > >Alvaro 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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