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Subject: Re: An MTD(f) question about NULL MOVE searching

Author: Fabien Letouzey

Date: 06:31:02 07/16/04

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On July 16, 2004 at 09:21:12, Vasik Rajlich wrote:

>On July 16, 2004 at 09:13:07, Fabien Letouzey wrote:

>>Yes, but a PV node does not necessarily end up in the PV (e.g. fail high).
>>Therefore "PV node" and "PV" are different concepts.

>I am not sure I understand this distinction. Do you mean that PV node is a node
>which you score between alpha and beta, and PV is the variation which eventually
>emerges? (Ie pv nodes can be "overwritten")


No by "PV node" I mean a node that is beeing re-searched in PVS.  So I assume
only a-priori information (the scout search failed high), it is not known yet
whether the score will end up exact or bound.

It's true that there is another definition of "PV node" in game-tree search,
in-line with the definition of a PV.

However I think that, when talking about PVS-like algorithms, the most common
meaning is the former (e.g. beta != alpha+1).  This is because of the
possibility of doing things differently at those nodes in PVS.


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