Author: Robert Hyatt
Date: 11:32:50 11/05/01
Go up one level in this thread
On November 05, 2001 at 07:00:48, Tord Romstad wrote: >On November 04, 2001 at 17:41:06, Michel Langeveld wrote: > >>Don't forget to look at Bruce Mooreland's excellent homepage about >>computerchess: http://www.seanet.com/~brucemo/toc.htm > >This looks like a very good site --- thanks to you for mentioning it, and >to Bruce for writing it! > >I was a bit surprised to see the suggested implementation of the null move >heuristic on Bruce's homepage, the alpha-beta window is different from what >I have always used. This is the code fragment: > > MakeNullMove(); > val = -AlphaBeta(depth - 1 - R, -beta, -beta + 1); > UnmakeNullMove(); > if (val >= beta) > return beta; > >In my code, I have something like > > val = -AlphaBeta(depth - 1 - R, -beta, mate_value); No reason. All you want to do, is with minimal effort, prove that if you do _nothing_ the score will return >= beta. Whether it is > beta, or = beta means nothing here. using mate-value means you will not be able to prune many lines in the null-move search that would be discarded by alpha/beta with X, X+1 as the bounds. > >which I always thought was the normal way of doing things. The advantage >of my method is that I can often detect serious tactical threats, while >Bruce's approach has the obvious advantage that it searches fewer nodes. >Without extensive testing, it is not clear to me which technique works >better. > >What alpha-beta window do the rest of you use? If anybody has tried both, >which approach works better? > >Tord I've always used X,X+1 for null-move. I've tried others, but none were as efficient. I don't see how it would matter if the score is == beta, or way above beta. All that says is that you are winning, or you are _really_ winning, without having to play a move. Now if the null-move search fails _low_ that tells you something. IE the difference between alpha and alpha-100 would be interesting. Alpha means doing nothing is not good. alpha-100 failing low means doing nothing loses a pawn. Which may mean the opponent has a serious threat that you have to actively hold off by playing a move.
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