Author: Sune Fischer
Date: 10:17:52 09/28/02
Go up one level in this thread
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? 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. "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. >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. >Uri
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