Author: Ed Schröder
Date: 00:26:29 10/31/99
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>Posted by Robert Hyatt on October 30, 1999 at 10:08:51: >>What Bob describes over there is the OLD (original) approach of null-move see >>my other posting on this topic. It is only about pruning on ply-1 situations. >> >>Nowadays null-move is done in the whole tree, quite a difference. >> >>Am I wrong about this? >> > >Very definitely wrong. Let me give you the complete details: > >Cray Blitz (late 80's) used a null-move search, where a null-move could be >played _one_ time in a single path. (this is called non-recursive null-move >search since only one null move is allowed anywhere between the root and the >tip.) I (and Campbell) also tried recursive null-move, which would allow >multiple null-moves anywhere in the path (as we do today) but I could only >test this on slow hardware (a Vax) and the 5 ply searches it could do really >suffered to horizon effects dealing with mate threats, just like today's null- >move programs suffer if the depth is limited or the time is short enough). > >I also (as did Campbell) try R=2 but at those speeds (It turns out it would >have >worked fine on the Cray since we were doing 9-10 plies then and we would have >been maybe 50 or so points stronger based on testing on today's hardware which >is fairly close to the 1988 hardware speed of CB) on the Vax, R=2 seemed to be >terribly risky and lost more than it gained. > >Today I am using a dynamic null-move R factor, R=3 close to the root, R=2 >closer >to the tips. I use recursive null-move, but don't allow two null-moves in a >row. > >The main difference between what I do now and what I did then was that in 1988 >I wasn't doing recursive null-move, and in 1988 I used R=1. But I (and >Campbell) had tested with code _identical_ to what I use today. You just described what I have been trying to point out all the time. The evolution of a bright idea (do something with doing nothing) to a full developed and powerful selective search good for hundreds of elo points for many programs. Ed
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