Re: computer-go: A problem with understanding lookahead

["Eric Boesch" <ericboesch@xxxxxxxxxxx>]

You seem to understand perfectly.  There is no guarantee that more lookahead 
will yield better results, although it usually does.  I have unintentionally 
written lousy game evaluators whose 8-ply performance was worse than their 
6-ply performance.  A professor at the University of Maryland published a 
paper proving that more lookahead may create worse results on average under 
certain plausible conditions.  I believe that the main disadvantage, apart 
from the time wasted, is that the more lookahead you have, the more 
evaluations you do, and the more likely it is that your evaluator will bump 
into situations where its evaluation is off-base.

> From: "GL7: David Elsdon" Reply-To: computer-go@xxxxxxxxxxxxxxxxx To: 
> computer-go@xxxxxxxxxxxxxxxxx Subject: computer-go: A problem with 
> understanding lookahead Date: Tue, 16 Jan 2001 21:03:22 +0100
>
> Hello all,
>
> I have a serious problem with lookahead. I don't understand why it works. 
> Why should the backed up values of a, say, 7 ply full width alpha-beta 
> minimax search be any better than the values my evaluation function gives 
> me by simply evaluating the positions at ply 1. I can understand that if 
> the end of the game is in sight then lookahead is useful. I can understand 
> that if I use a quiesence measure or some such and only evaluate positions 
> when I know that my evaluation function will work best then lookahead is 
> useful. But if neither of these is the case then does lookahead help. Is 
> there some way in which the backing up of values and minimaxing somehow 
> reduces the error in the evaluations.
>
> I really am seriously stuck with this one.
>
> Cheers
>
> David
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