# Computer Chess Club Archives

## Messages

### 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 );
}

```