Author: blass uri
Date: 07:32:52 04/01/00
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On March 31, 2000 at 23:17:45, Robert Hyatt wrote: >On March 31, 2000 at 12:53:43, Stephen Ham wrote: > >>Dear Readers, >> >>I know many of you are actively following my ongoing match games versus Fritz 6a >>and Nimzo 7.32. For those of you not familiar with the event, please visit: >> >>http://correspondencechess.com/campbell/index.htm >> >>Anyway, a frequent poster here (name is withheld) wrote to Mr. Campbell stating >>that since the chess engines are displaying their top 3 choices, they are being >>weakened "a lot". No explanation was given for that claim. >> >>Would somebody here please provide a detailed explanation regarding whether this >>claim is correct and why? > > >It depends on how they compute these variations. Done correctly, it is >_horribly_ inefficient. If you watch a normal search, the first move will >usually take over 50% of the total time. The remaining N-1 moves take the >remaining 50% of the time. If you have it display two 'best'moves, you >increase the total search time by roughly 50%. The first move takes the >same time as before. The second move also takes the same time as before, >and the final N-2 moves take just a tad less than before. Net loss is >ugly. If you have it display the best 3 moves, you slow it down by exactly >a factor of two... > > > > >> >>The chess engines are on settings recommended by ChessBase USA as their optimal >>settings for this event. My extremly limited understanding is that displaying >>the top 3 choices does indeed affect the chess engines, but it causes them to >>spend more time on what it believes to be the 3 best moves. As such, this sounds >>like an enhancement to me. Given that the chess engines are allowed about 24 >>hours calculation time on weekdays and are searching to 16-18 ply, I can't >>imagine that this weakens them in any way. > > >Each iteration will take about 2x longer than the previous. Rather than >a branching factor of 3x, you raise it to 6x. This will cost several plies >over 24 hours. My experience with chessbase engines show that it is not the case. I also see no reason that the branching factor will change. The program is going to be slower by a constant factor by calculating the first 3 moves. The only difference relative to calculating only the best move is that you need to use time to calculate the second best move and the third best moveand I do not see a reason to be more than 3 times slower. The only case when the branching factor is going to be bigger is if you generate a tree of moves and not only the best 3 moves. Uri
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