Author: Peter McKenzie
Date: 22:20:41 08/14/01
Go up one level in this thread
On August 15, 2001 at 00:06:00, Robert Hyatt wrote: >On August 14, 2001 at 21:51:49, Dieter Buerssner wrote: > >>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. >> > > >If a call to search returns a value < alpha, I return that value to the >previous ply, not the original alpha. But if you search each move at a ply, >and you get a score <= alpha for each, you can _not_ reasonably expect those >scores to reflect anything about which move is better. It just doesn't >work like that. At the next ply you fail high as soon as you find a score >>= beta. Not necessarily on the _best_ move, just on _any_ move that will >produce a score >= beta. And since you don't search all moves to find the >largest fail-high, how can you use tht result at the previous ply to find >the worst move? Answer is, you can't, reliably. Hi Bob. I think we all understand what you are saying in this paragraph. But lets for a moment assume that when you fail high, your move ordering is so good that you fail high with the best move *most* of the time. We will call this ratio the FHBest ratio, being the number of times you fail high with the best fail high move divided by the total number of fail highs. Now of course, we can't measure FHBest unless we do a true fullwidth search, but lets just assume that it is high. If FHBest is sufficiently high (don't ask me how high is sufficient :-), more often than not we could determine the best fail low move. We aren't *certain* that it is the best fail low move but, if FHBest is high enough, we know that it *probably* is the best fail low move. So it would make sense to give the probable best fail low move a bump up the move list when re-searching this position at a later time. Peter
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