Author: Robert Hyatt
Date: 06:41:02 06/15/98
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On June 15, 1998 at 04:52:16, Dezhi Zhao wrote: >In some earlier posts by Don Dailey and others, they mentioned >about zero-width window null move search and said it's an efficent >way to implement null move search. So I compared the zero-width null >move to the original full-width with my Xiangqi (Chinese chess) PVS >engine. >Here is the results of playing 20 moves (same path for both method, >without opening book) from the initial position. > >The m/c usually searches 2 to 4M nodes for each posoition. >If the transposition table is cleared between searches, the savings >of zero-width are generally around serveral hundreds of nodes, >and the max is 9K for one position. >If the transposition table is partially cleared (keep only last >iteration >entries) between searches, the savings become hard to interpret. You >save several hundreds of nodes in a postion, lose that in the >following position, and ocassionally lose much more than than previous >saving (save 8.4K and lose 140K in the next for example). > >I think that the savings are negligible, which are caused by the fact >that in PVS most of the nodes are of zero-width window already. > >These results also remind me of the word "vapor-ware" that Dr. Hyatt >called NegaScout over PVS. So I checked Crafty 14.13 again, and found >that Crafty uses full-width window null move search. Why? My best guess >is that Dr. Hyatt has done extensive tests over null move search >abnormaly >as he mentioned several times in CCC, and found null move search window >is >related to the abnormaly. Am I right? no... I do it that way simply because 99.999% of the nodes searched are already using alpha,alpha+1... There is nothing wrong with doing every null-move search using beta-1,beta, for example, and it probably makes sense to do it that way, I just did not because of PVS already taking care of that for the most part. I will run some tests to see if it makes any difference at all, but suspect that it will have virtually no effect, because it will only affect a very few searches, total...
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