Author: Dieter Buerssner
Date: 11:41:07 02/26/04
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On February 26, 2004 at 06:59:37, martin fierz wrote: >another reason for not believing this stuff: your above graph shows *exactly* >what happens when you go from a non EGTB position to an EGTB position (or, for >that matter, what happens when you go into any position your program can >recognize as a draw whether it has tablebases or not): your eval thinks it's >doing great, but the exchange of something leads to a drawn position in your >tablebases. are you going to claim that crafty plays better without TBs? >:-) Some interesting related reading about this: E.A. Heinz. Efficient interior-node recognition. In ICCA Journal, Vol. 21, No. 3, pages 156-167, September 1998. (Download at http://supertech.lcs.mit.edu/~heinz/ps/node_rcg.ps.gz) At page 3, they discuss, how to score certain known results (win or loss, but not the distance to win/loss). 2 methods (my paraphrazing): Have a scoring range outside the normal eval scores but lower (in magnitude) than the "real" mate scores. Or just give rather normal eval scores. They started with the first method, and went to the second (although the first method sounds better at first sight). In my engine, I can compile TB-returns as fail hard (return beta or alpha) or as fail soft (return the mate score or 0.0). Default is fail soft. Some time ago, I found some positions, where the fail hard method used significantly smaller trees (the engine uses fail-soft search, normally). I really could not explain it well, but also did not invest lots of time, to try to understand it. I also remember some private mail from Ernst Heinz (about fail hard/soft). Heinz (probably out of convincing arguments :-): "Fail hard läuft einfach besser". Regards, Dieter
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