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Subject: Re: Correct values if all moves are pruned?

Author: Jon Dart

Date: 13:02:22 01/05/01

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On January 05, 2001 at 15:21:18, Severi Salminen wrote:

>Hi!
>
>1.If I prune a move in normal search: if(material+gain(move)+FMARGIN<=alpha)
>what should I assign to the best score so far? Material+gain, material+FMARGIN,
>material+gain+FMARGIN or material only? Now I'm using material+FMARGIN but it
>can't be right. Material+gain sounds right because that would be returned from
>qsearch if stand pat fails high?
>

I'm having a little trouble understanding this.

Anything that's forward-pruned can't affect the score. If you don't
search it doesn't have a score. Plus the reason you're not searching it
is because you believe it can't return a value > alpha, which is
the only way it could affect the score or the best move.

>2.I'm using now SEE and I wonder what is the "correct" value to return from
>qsearch if I prune all captures: if(eval()+seescore(move)+MARGIN<=alpha)? Now I
>just return alpha. If all moves result a score<=alpha should I return
>eval+seescore or something else.
>

I believe the correct answer is alpha. You only change the score and the
best move if you've found a move > alpha. Note though that in the qsearch
you can bail out before searching any moves if your stand-pat score
causes cutoff.

>I ask this because PVS or aspiration window search doesn't seem to like "wrong
>values"

That's for sure.




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