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### Subject: Re: negascout and PVS?

Author: Tim Foden

Date: 06:05:32 07/27/04

Go up one level in this thread

On July 26, 2004 at 19:47:21, Peter Alloysius wrote:
>What's the different between negascout and PVS ? They look like the same
>algorithm to me.
AFAIK there is only really one difference, which is the (d < maxdepth - 1)
below. In PVS it would be (d < maxdepth), or (true). NegaScout uses the fact
that, if there is no quiescence search, then a zero window search will suffice
for the last ply. I couldn't be sure of this explanation though. :)
Cheers, Tim.
From http://www.zib.de/reinefeld/Research/nsc.html given in another reply:
int NegaScout ( position p; int alpha, beta );
{ /* compute minimax value of position p */
int a, b, t, i;
determine successors p_1,...,p_w of p;
if ( w == 0 )
return ( Evaluate(p) ); /* leaf node */
a = alpha;
b = beta;
for ( i = 1; i <= w; i++ ) {
t = -NegaScout ( p_i, -b, -a );
if (t > a) && (t < beta) && (i > 1) && (d < maxdepth-1)
a = -NegaScout ( p_i, -beta, -t ); /* re-search */
a = max( a, t );
if ( a >= beta )
return ( a ); /* cut-off */
b = a + 1; /* set new null window */
}
return ( a );
}

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