Author: Peter Fendrich
Date: 07:18:27 03/10/03
Go up one level in this thread
On March 04, 2003 at 11:04:00, Robert Hyatt wrote: >On March 04, 2003 at 05:04:55, Sune Fischer wrote: > >>>Note that I don't know of anyone extending when there is only one legal move. >>>The >>>original algorithm was "one legal reply to check" which means you are in check >>>_and_ >>>you have only one way out. >> >>Well _I_ want to extend in this case :) >>Anyway, I don't think "original algorithm" necessarily means "optimal algorithm" >>;) >> >>I think it is related to the re-capture and singular extensions, only problem is >>how to actually "remember" the only move, on my movelist moves are deleted after >>being searched... grrr what a drag. > >I'll bet that if you extend only on one legal move and not in check, it will >only fire a >dozen times during an entire game. One legal move is _very_ rare if you aren't >in check. >One "logical" move is a different matter. We played with an option "one sane >reply" which >is more general. Peter Gilgasch proposed it to me and I tried it in Cray Blitz. > The idea is >that often you have 2-3 ways out of check, but all but one lead to your getting >mated. So you >extend the one that doesn't get you mated so that you can see deeper to possibly >see a mate >there as well... > >It is pretty expensive to do this, however, and I didn't keep it very long >because I was >beginning to work on the singular extension code and it is a super-set of this >kind of >"one-sane-reply" extension. > >> >>While on the subject, how does one detect singular moves? > >Singular as in deep blue? > >For a move on the PV, search the first move with the normal window a,b. Search >the >remaining moves with the window a-s, b-s where s is the "singular margin, I >think I >used 3/4 pawn or something similar as they did in DB. If all moves fail low, >except >for the first one obviously, then the first move is significantly better than >the rest. But >if one fails high, you have to test _it_ for singularity by seeing if it is "s" >better than the >original best move. > >For fail-high nodes the same idea but it is expensive. You fail high on move X. > Normally >you would exit _right now_ returning beta, but you first test all the other >moves with the >offset (downward) alpha/beta window, but you search to reduced depth to control >the >cost. If the rest of the moves fail low, the fail-high move is singular. >Re-search it with a >deeper search. > >There is another way to do "pseudo-singular" I can describe if you want... Yes, Please! /Peter
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