Author: José Carlos
Date: 15:29:06 08/20/00
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On August 20, 2000 at 18:15:48, Robert Hyatt wrote: >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... This suggests me an idea, I don't know if it has been tried: Suppose you've searched all moves at depth d. Then, at depth d+1, the PV move has a bigger value then at d. In that case, you could simply go to d+2 without looking at the rest of the moves. Only when the PV value drops down at any depth, search the rest of the moves. Just a thought... José C.
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