Author: Dieter Buerssner
Date: 10:09:16 10/15/01
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On October 15, 2001 at 04:28:42, José Carlos wrote: > In Averno I haven't seen this problem yet. I simply order queen promotion >before other promotions. I do the same. And, I usually do not see this problem. But I have seen it. >So if the promoted piece is taken, the different lines >will lead to transpositions and be quickly discarded. In the lines where the >piece is not captured, the line with the queen on the board will yield the best >material score. > Then I don't understand how this can be a problem is move ordering is correct. I feared, that I failed to express myself clearly ... First, this may all depend on many details, including the replacement scheme used for hash tables. Of course, when we get a hash hit immideatly after a capture of the promoted piece, we will get the same score for the different promotion pieces. If not, we start to search. But now, we search the tree with a differently filled hash table. And in general, we will search a different tree, because of this, and we may get a different score. (Similarily, many programs find the solution at different search depths for Fine 70, when the HT size changes). It may be, that we get a hash hit later, that cuts off the tree, that really has more depth than needed. I think it is obvious, that this can change the score. Another thing are path dependent extensions, for example recaptures. We get a cutoff for the same position, but if we would search, we would use different extensions (depending on the last move(s)), and therefore get a different score and/or PV. One may be able to fix this, by storing some path information, but I guess nobody does this consequently. I actually tried, but it only worsens things, because the HTs get less efficient. Other examples (50 moves rule/repetition) or discussed in Dennis Breuker's thesis under GHI (graph history interference?). I think, a link is available at the "CC recsource center". Then, in general we will start to search e8Q and e8B with different windows. This can yield in different pruning/extension decisions. I think, this is very related to the problem, of failing high in zero window search, and a later fail low when searching the same depth with a wider open window. I think it is just unavoidable, when not using some plain alpha-beta search without HTs. Regards, Dieter
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