Author: Uri Blass
Date: 00:46:37 02/21/02
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On February 20, 2002 at 18:30:25, David Dory wrote: >Uri, > >Forward pruning has been a proposed answer to effeciently limit the size of the >search tree since the early days of Dr. Shannon. > >Unfortunately, no one has found a way to throw out the dirty bath water, without >dumping the baby out also, so to speak. > >For a good discussion on this from an expert, take a read of Chess Skill in Man >and Machine. This was one of the big differences between CHESS 3.6 and CHESS 4.5 >You may recall that the Northwestern University Chess Program CHESS was world >champion, several years. > >Quote from page 92 of the above: (Slate and Atkins) > >"The implementation of full-width searching had immediate beneficial results." > >The authors go on to say the correct search would indeed include a smaller tree >using various techniques, some of which were not perfected. > >They give this diagram as an example of the problem of forward pruning: > >[d]2k5/3p4/b2p3p/1p1Pp1pP/pP2P1P1/P2N1K2/8/8 w -- > >the move Nf2 would, he felt, surely be pruned out. However, a full width search >easily finds a nice knight's tour: Nd1, Ne3, Nf5, Nxh6. > >I think you'd be amazed at the number of "special cases" you would have to >program into a forward pruner. In particular, I think you'd be adding such >"special cases" until you realized you had slowed the program down so much, it >was actually _weaker_ than a full-width program. > >There must be a better way to make a stronger program than forward pruning. > >Dave I did not try rules for forward pruning at the root on my program and I said that I believe that the task is too hard for one or 2 programmers but if I have some millions of dollars to invest in a chess program then I may try this idea. Uri
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