Author: Christophe Theron
Date: 11:29:34 03/08/99
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On March 08, 1999 at 13:48:48, Steve Maughan wrote:
>I have come across NegaScout and am wondering if it would be worth implementing
>in my program. I understand the principle but what is the payoff? How many
>extra ply (if any) would it give over a plain old Alpha Beta search? Is it ever
>slower than Alpha-Beta? Does (virtually) everyone do it?
>
>All help appreciated!
>
>Steve Maughan
NegaScout won't give you an extra ply of depth, but it is nevertheless a
significant speedup.
The drawback is that in some programs that use the values of alpha and beta to
selectively prunes some subtrees you can have consistency problems when
re-searching. It used to be a problem for me when beta=alpha+1 (which happens
very often with NegaScout). Hash table management can even make things worse.
But after all, if you succeed in fixing these quirks, NegaScout is slightly
better than AlphaBeta.
I am still keeping an eye on it in the current versions of Tiger. I have a
"#define NEGASCOUT 1" that I can set to 0 to go back to simple AlphaBeta. From
time to time I run some tests to be sure NegaScout is better. It is indeed, but
not by much.
Christophe
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