Author: Dieter Buerssner
Date: 18:51:49 08/14/01
Go up one level in this thread
On August 14, 2001 at 00:37:15, Robert Hyatt wrote: >On August 13, 2001 at 14:07:43, Dieter Buerssner wrote: > >>On August 13, 2001 at 00:01:35, Robert Hyatt wrote: >> >>>On August 12, 2001 at 23:49:35, Pham Minh Tri wrote: >>> >>>>How about the UPPER? Should we choose the move has score nearest alpha (the >>>>highest score or the first of highest ones)? Perhaps store something is better >>>>than nothing. >>>> >>> >>>Nope. Something is not better than nothing here. In a LOWER position, every >>>move was refuted by the next ply. Much snipped, but I will come back to this later. >Note that I use fail-soft as well. Then, I must totally misread your source. You don't keep track of the best score, when it is lower alpha. You allways return alpha, in the case of an upper bound node. This will move earlier be beta. So, this looks essentially as fail hard to me. > But the bounds you get back, while they >can be below alpha, are _still_ useless to choose which of the moves is the >best one. They _might_ give you a better idea of what to do about changing >the lower bound on the re-search, but not to choose the best of the worst... I am very well aware of the fact, that the scores you get back outside of the window, are not trustable at all. Still, I have mentioned the case, of all scores beeing losing mate scores, but one is not. This move will be good to try first. I have seen this, by investigating multi MB large tree dumps, so it is not only there in theory. Often, even with fail soft, I of course will also get multiple moves with the same score (alpha). But then one can see the "best" move as an additional killer move. It was most probably the killer move anyway, when this position was visited the last time. I cannot see a reason, why trying such a move early could hurt. And I do see reductions of tree sizes. I don't try upper-bound moves first. I try them (more or less) after the good captures, and together with the killer moves, but before history moves. >The terminology is a bit unclear, but I am using the words UPPER and LOWER the >same way most others do. > >A position marked "UPPER" means that all moves failed low, and the bound we >store is the _upper_ bound for that position, because we know all scores are ><= that bound. We don't know how bad the score is however. Nor do we know >which move was best as all are simply known to be <= some value. > >A position marked "LOWER" means that the move played there failed high, but >all we know is that the score is >= some value. IE "some value" is the >lower bound for this position but the real score could be much higher. Hence >the name "lower". And here we _do_ have a best move, the one that failed >high. > >It seems backward, but LOWER means a fail high node, while UPPER means a >fail low node. If you use that terminology everybody will understand what >you are saying. If you use the obvious terminology, you will be using the >opposite of everybody else and that will cause some interesting miscues. :) I believe, I am using the terminology, you are describing here. But to me it seems, that in the sentance I cited at the start of my post, you don't use this terminology. Sure, sometimes I may have a big problem in reading comprehension. But I tried, to rearead again and again. What you named "LOWER" above, seems to be upper to me. In an upper bound position, every move gets refuted at the next ply. In an lower bound position, you find a move, that cannot get refuted at all. Regards, Dieter
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