Author: José Carlos
Date: 05:29:05 08/28/00
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On August 27, 2000 at 21:52:05, Robert Hyatt wrote: >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. Yes, in most cases, but I don't have null-move in Averno, and experience those fh-fl from time to time. Some people here (I think Ulrich Tuerke and some other) explained how this can come from hashing too, and seemd very clear to me. José C. >> >>Cheers, >>Tom
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