Author: Georg v. Zimmermann
Date: 15:44:04 08/20/00
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On August 20, 2000 at 18:29:06, José Carlos wrote: >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. This seems flawed to me 1.) Lets say at ply7 you think position is equal at ply8 the first move searched turns out to win the queen, but the second would mate ? Why skip it ? 2.) If I go to d+2 with move1 immediately the other moves will not get better sorted. 3.) The first move takes longer to search than the others anyway. Of course, I might have missed something. Regards, Georg v. Zimmermann
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