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

Author: Vasik Rajlich

Date: 06:42:45 07/16/04

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On July 16, 2004 at 09:31:02, Fabien Letouzey wrote:

>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.

Ok, got it. The MTD (f) equivalent is (I guess) a node which fails both high and
low. The problem is that you don't know this when you make the first visit. The
inability to force a null move to "really fail high" is just one instance of the
information you lose ...


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