Author: Vincent Diepeveen
Date: 10:09:31 06/15/98
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On June 15, 1998 at 10:53:49, Don Dailey wrote: >On June 15, 1998 at 09:41:02, Robert Hyatt wrote: > >>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... > >Bob, > >I'm not convinced that this is the case. Also it may not matter if >99 selective nodes are zero width and 1 is not if that one takes >significantly more time to search. > >I do not know that you are wrong either, I'm just not sure. When >I made this change I definitely got a noticable speedup, not huge >but enough to imply something was going on. > >If you make the change can you instrument this for us? You could >count the nodes that would be zero width and also count the non-zero >width nodes and report them to us. Theoretically it can never be worse to use beta-1 and beta. >- Don
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