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Subject: Re: Zero-width Window Null Move Search

Author: Ren Wu

Date: 09:41:26 06/15/98

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I did some experiments on this a while back, maybe 2 years ago, both on my chess
program and my chinese chess program. I can't remember the exact result, but the
experiment itself make me decide use  alpha, beta, instead a null window.

I used to use PVS but switch to NegaScout some time ago, but after that
experiment. So my result is from PVS and is agree with yours here.

What is your  "vapor-ware" story all about? I think i miss that post.

BTW what is your program's strength? what is its speed(nps)?

Ren (

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
>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
>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
>as he mentioned several times in CCC, and found null move search window
>related to the abnormaly. Am I right?

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