Author: Gian-Carlo Pascutto
Date: 05:12:09 06/03/01
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On June 02, 2001 at 17:44:38, Bruce Moreland wrote: >I do a test to see if there is apparently only one move that doesn't suck. I >do a reduced depth search. If the first few don't drive the score to something >close to alpha, I leave, because I assume this is a fail-low node. If one of >them drives the score pretty close to alpha, I check the rest to see if there >are any more that do this. Ok, I assume you do this before starting the normal search, but after nullmove etc? Before starting the normal search, you search every move with R=2/R=3 or something similar, and check whether there is one single move that produces a score close to alpha, whereas the remainder is clearly worse. You speed this up by exiting if neither of the first few moves gets near alpha. You can probably also speed this up (I have no idea whether you do it or not) by, after you have found a 'potential singular' move, exiting if neither of the following moves gets near alpha too. >If there's only one move that looks decent, I call it singular and extend it a >ply. A full ply? No fractional increments? >This doesn't work in the endgame, but in the middlegame I found it >improved solution times in the ECM suite dramatically, while costing a ply in >the general case. Intresting. So you found a definite tactical strength increase? Any numbers on WAC? >This extension made my search pretty unstable so I had to do some of the hash >table stuff mentioned in the DT article on singular extension published in the >ICCAJ some years ago. Ok. Do you also hash nodes where you did not find a singular move, i.e. the ICCAJ paper only mentions hashing positive results with stickyness, so even if the move is no longer singular we still pretent it is after a while. You could do the same for non-singular nodes. Do you? >The version that played in the WCCC 1999 used this. Don Beal came around >collecting program information and I told him then, so it may have already been >published in an ICCAJ. I don't have access to those, unfortunately :( Sorry for all the questions, but you're the only person I know of that is currently using singular extensions without seeing a noticable strength decrease. Since I've been trying to get them to work in Crafty for a while, this is very interesting. Mike Byrne sent me some code from Robert from 2 years ago that, as far as I can tell, pretty much seems to do what you describe, but it's got some weird things in there too, and I don't fully understand them. -- GCP
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