Computer Chess Club Archives




Subject: "Suspicious move" extension

Author: David Eppstein

Date: 11:35:11 11/20/97

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?

This page took 0.02 seconds to execute

Last modified: Thu, 07 Jul 11 08:48:38 -0700

Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.