Author: Uri Blass
Date: 10:25:12 09/28/02
Go up one level in this thread
On September 28, 2002 at 13:17:52, Sune Fischer wrote: >On September 28, 2002 at 13:06:48, Uri Blass wrote: >>>Okay, chess lingo question: how can I fail low on the first root move, the alpha >>>value is -inf? >> >>Not for me and I think that not for most of the programs. > >Probaby better to use some aspiration window you mean? Yes I do it. Today I use alpha=score-30 and beta=score+30 for the first move. Using a constant is not the best idea and it is better to increase the constant if the changes in the evaluation are bigger. >I tried null window but that always has to be researched on the first move. > >>>I don't do aspiration search or anything at the first move, should I? >>> >>>I do search the best move from the previous depth first, the rest are not sorted >>>in any way. >> >>Another mistake >>The rest should be sorted. >> >>If I understand correctly good capture can be the last move if the rest are not >>sorted in any way. >> >>I doubt if you really mean it and I guess that at least that you search captures >>before no captures also in the first ply. > > >Yes, I do sort them actually, but I search the move with the smallest tree first >(I forgot I did that). > >>>All I know is that the second move should never be better than the first, that >>>would be a sign something is wrong. >> >>The second move is often better than the first because programs often change >>their mind. >> >>>I guess I can call it a fail low for the >>>first move (relative to the second move). >>> >>>-S. >> >>I do not understand what do you call fail low. >>I call fail low only cases when I find that the first move is bad and I do not >>know exactly how bad. > >Fail low to me is when your best score is worse than alpha, that is impossible >at the first move if you start at -inf. I use alpha=score-30 so it is possible for me except cases when I already saw a mate against myself. > >"If the first move you search fails high (returns a score greater than or equal >to beta), you've clearly got a beta node. If the first move fails low (returns >a score less than or equal to alpha), assuming that your move ordering is pretty >good, you probably have an alpha node. If the first move returns a score >between alpha and beta, you probably have a PV node." > >http://www.seanet.com/~brucemo/topics/pvs.htm > >>Cases when the program change it's mind can be described as fail high >>because I do not know the exact score when I search with window of 1. > >Then I don't see how you can distinguish between fail lows and highs, they both >mean the program changes its mind. No For me fail low means that the the score of the first move is lower than alpha that is not -inf. I do not understand what you mean by fail low if you use -inf. > >>There are cases when the research does not verify the fail high and in these >>cases it is a wrong fail high and the program does not change it's mind. > >yes, Bruce calls it search instability I believe. Yes I have them. Uri
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