Author: Robert Hyatt
Date: 15:15:48 08/20/00
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On August 20, 2000 at 16:13:22, Frank Phillips wrote: >Can anyone sketch out the singular extension algorithm. I found some general >information on the net, but nothing that helps me understand how to implement it >in a PVS alpha/beta search. Descriptions tended to mention only that it is >invoked when there are only a few good moves in a variation. Since alpha/beta >does not yield the value of moves other than the principal variation, I am not >sure what this means in practice. > >Frank The simple case is on the PV search. When you search the first (and hopefully best) move at each ply, you search the remainder of the moves with alpha-w, beta-w, where w is some window offset (say 1/2 pawn). If all the other moves still fail low, then the 'best' move is better than the remaining moves by at least 1/2 ply. You re-search the 'best' move one ply deeper. Ie some programs search deeper if there is only one legal way out of check. Suppose there are three legal ways out, but two of them drop all kinds of material. There is only one "reasonable" move and singular extension will follow it more deeply than the other two 'silly' moves...
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