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Subject: Re: Q. Aspiration, PVS, Fail-Soft

Author: Scott Gasch

Date: 14:22:15 07/02/04

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On July 02, 2004 at 12:28:31, Fabien Letouzey wrote:

>On July 02, 2004 at 12:07:42, Volker Böhm wrote:
>
>>On July 02, 2004 at 09:21:41, Fabien Letouzey wrote:
>
>>>Bruce makes a slightly different assumption that depends on the
>>>window.  IMO it is an uncommon implementation but it might be better
>>>depending on aspiration windows.
>
>>What does Bruce suggest? Btw. who is Bruce, Bruce Moreland?
>
>Yes Bruce Moreland.  His tutorial is famous, but it seems his description of PVS
>is not the commonly-used algorithm:
>
>http://www.seanet.com/~brucemo/topics/pvs.htm
>
>Fabien.

Bruce's tutorial doesn't start to search with a minimal window until it find a
PV node (i.e. until a score returned beats alpha).  What if you are on, as bruce
calls it, an "alpha node" (where everything is gunna fail low)?  If your move
ordering is good then you should still search the best move first.  Therefore
you can speed things up even more by searching the rest of the moves with a
minimal window (the thought being that they are all worse than the first move).
Bruce's implementation searches all of these moves on alpha..beta if one has not
yet beat alpha.  Maybe it's blasphemy, but I think the "traditional" PVS
implementation is better, assuming you have a good move order.

Scott



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