Author: José Carlos
Date: 14:53:03 08/28/00
Go up one level in this thread
On August 28, 2000 at 09:56:22, Robert Hyatt wrote: >On August 28, 2000 at 08:29:05, José Carlos wrote: > >>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. >> > >It can definitely happen without null-move. With null-move, it happens _far_ >more frequently. Mmmm, a good reason for a lazy programmer not to implement null move... :) José C. >>>> >>>>Cheers, >>>>Tom
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