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Subject: Re: Suspicious Move Extension

Author: Roland Pfister

Date: 23:51:00 11/20/97

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On November 20, 1997 at 14:35:11, David Eppstein wrote:

>I thought I would share with the group a technique I tried yesterday, to
>get the program I'm working on to play better in a class of positions
>where it was having horizon-effect problems.
>
>I identified a class of "suspicious moves", moves that are a priori
>unlikely to be correct but that are reasonably likely to be used as
>delaying tactics in the horizon effect (and that were in fact occurring
>in the horizon effect problem positions I was looking at). The moves I
>classified as suspicious were non-captures when a seemingly good capture
>is available. The move ordering I use naturally places these moves later
>than the captures, as I think would be true in many or most programs.
>
>Anyway, if I search a suspicious move and it appears worse than
>previously searched moves at the same node (i.e. below alpha), I trust
>that result.  But, if it comes in greater than alpha, I immediately
>become suspicious and search the same move to one greater ply. The
>deeper search result then becomes the value of that move.
>
>The intention is that this extension doesn't blow up the search tree
>size very much (because suspicious moves are rarely chosen as best) but
>improves the search accuracy. It is hard to be objective, but my program
>does seem to be playing better after this change.
>
>Is this technique common in other programs?  Can anyone suggest
>refinements that would make it work better?

I tried the following extension:

if the hash move is a move that does not capture the last moved piece
even if it would be possible and would be good (statically) and it
doesnt capture a better or equal piece, extend one ply.

That was intended to work in positions where one side puts a piece
en pris and has a threat so that the opponent can't capture that piece.

I discarded it because it made my tree bigger and the search slower( in
Bratko-Kopec ) without getting better results.

I will try your idea. Let's see what happens.

Roland



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