# Computer Chess Club Archives

## Messages

### Subject: Re: negascout and PVS?

Author: Daniel Clausen

Date: 03:17:53 07/28/04

Go up one level in this thread

```On July 28, 2004 at 05:47:53, Fabien Letouzey wrote:

>On July 28, 2004 at 05:16:24, Russell Reagan wrote:
>
>>On July 27, 2004 at 06:39:25, Fabien Letouzey wrote:
>>
>>>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.
>>
>>How is "original PVS" different from Bruce's version? I learned Bruce's version
>>first... :)
>
>OK, ignoring the PVS/NegaScout differences, normal PVS is:
>
>1) search the first (leftmost) move with full window
>2) use a scout search (null window) for all other moves
>
>The assumption is that the first move will often be the best one.  Bruce's
>assumption seems to include the aspiration-search assumption (the final score is
>likely to be inside of the window).
>
>Of course if aspiration is not used, both algorithms give the same result.
>
>Fabien.

I get more and more confused. :)

I liked the summary Pham gave in his previous post:
(http://www.talkchess.com/forums/1/message.html?379139)

: negascout:
: 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

: pvs:
: 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

Do you agree with these "definitions"? If yes, isn't the algorithm Bruce
mentions (http://www.brucemo.com/compchess/programming/pvs.htm) _exactly_ what
PVS means?

Sargon

```