Author: Robert Hyatt
Date: 18:52:05 08/27/00
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On August 27, 2000 at 17:33:15, Tom King wrote: >Hi all, > >a question for programmers on fail highs. > >what do you do in your program if a fail high is encountered, which on the >research fails low? Two answers. First I use PVS, so keep this in that context: 1. if the null-window search fails high, but the re-search fails low, I ignore it totally. 2. If the null-window search fails high, _and_ the re-search (with the aspiration window) fails high, then I keep the move as best, even if the re-search with beta,+infinity fails low... > >I've ignored this issue, because it doesn't seem to happen all that often (in my >program). So if my program finds a move which fails high, even if the research >indicates that it maybe shouldn't have failed high, it thinks the move is good. >Maybe this is bad? At the WMCCC recently, I noticed a couple of these fail high/ >fail low moves cropping up at critical, complex positions. Often I was unhappy >with the move my program chose in these cases. Perhaps these fail high/ fail low >moves need to be treated with suspicion? Perhaps. I have found that the null-window fail high can't be trusted, but since that is verified with a subsequent alpha,beta re-search, it might fail low and get ignored, or fail high and get re-searched a third time with +infinity for beta. Seems safe enough. But when this is happening, strange things are going on. If you turn null- move off, most of these fail high/fail lows go away... so that is the source of the problem. > >Cheers, >Tom
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