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Subject: Re: negascout and PVS?

Author: Fabien Letouzey

Date: 03:39:25 07/27/04

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On July 26, 2004 at 23:48:46, Pham Hong Nguyen wrote:

>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.

>Yes, they are the same BECAUSE some computer chess writters think they are the
>same ;)

I can't agree more with this, the main confusion comes from first confusing them
into beeing the same :)

>I have read that someone has written that Negascout is just another way of
>implemention of pvs or vice versa.

That's also my way of seeing it, reformulating PVS into a single function.

>At first glance, they look quite similar: both are based on AlphaBeta, both use
>aspiration search with zero window, both have to research if new value falls out
>of this window. However, they differ each other in only small but important
>detail: first move vs bestmove.

>1) Search with full window for the first move
>2) Search with zero window for the rest moves (it means from the second move)
>3) Research with full window if new value falls out of zero window

>1) Search with full window if the bestmove has not been found yet (or the alpha
>has not been updated)
>2) Search with zero window for the rest moves
>3) Research with full window if new value falls out of zero window

>In my experiment, pvs can help to save much more nodes than negascout.
>I think Bruce Moreland did the best discription about pvs in his web.

I think this difference is Bruce's own interpretation and does not represent the
original PVS algorithm.  I think that, in the official articles, both PVS and
NegaScout use what you describe as "negascout" here.

I might be wrong.

It seems Bruce's modification is an attempt to integrate the aspiration-search
assumption with PVS.  This is interesting.


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