Author: Robert Hyatt
Date: 09:05:33 08/29/05
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On August 29, 2005 at 11:55:17, Gian-Carlo Pascutto wrote: >On August 29, 2005 at 10:05:41, Robert Hyatt wrote: > >>The problem is that you then introduce errors. I only probe (on the quad 875) >>when a capture takes the board to 5 or less pieces, and I have all 5-piece >>tables on that box. I don't probe in the q-search at all, although some do and >>I used to. I can't see how you could reduce that without introducing >>significant errors. >> >>Years ago I used to limit the depth at which I probed, to keep the NPS from >>dropping too far. And saw too many mistakes where it would push the critical >>capture beyond the probe horizon, so that it could still think it was winning or >>whatever. And it would enter a forced line because of that, thinking it was >>winning, when it was forcing a draw... > >1) I haven't seen this effect. > >2) Should it work as you describe, it would still happen. I looked at Crafty and >you limit probing to <= iteration depth, you can search a lot deeper, especially >with some spite checks or pawn pushes. > >3) What about 6 men? > >-- >GCP I am using almost all 6 man endings on my dual xeon, and am not seeing anything worse than what I saw with 5's only. The severe slowdowns are rare, but happen either way... Yes I limit the probe depth somewhat. My question was, how could I safely limit it further? Every ply it is limited has an associated risk. I still see positions where the q-search thinks it is reaching a won position, but it is not, because I don't probe out there as some do... I tried a _bunch_ of different limiting schemes over time, including one "adaptive" scheme that dynamically limited the depth-to-probe-at based on the NPS of the search. It would notice an excessive slow-down and reduce the depth at which probes were done to avoid losing too much. Turned out to cause other problems related to hashing and EGTB scores...
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