Author: Omid David
Date: 14:27:50 07/11/02
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On July 11, 2002 at 17:20:36, Andrew Dados wrote: >On July 11, 2002 at 16:38:50, Omid David wrote: > >>As part of an extensive research (will be published soon), we tested null-move >>pruning with fixed depth reductions of R=2 and R=3 on about 800 positions of >>"mate in 4" (searched to depth of 8 plies) and "mate in 5" (searched to depth of >>10 plies). The results naturally show that R=2 has greater tactical performance >>(greater number of checkmate detection). However, we also conducted about >>hundred self-play matches under 60min/game time control between R=2 and R=3. The >>outcome is a rather balanced result (R=2 only a little better). Considering that >>the tests where conducted on a rather slow engine (100k nps), on faster engines >>R=3 is expected to perform better. >> >>So, apparently R=2 is not _by_far_ better than R=3 as some assume. I believe >>Bruce Moreland had also some good results with R=3 that show it's not too >>inferior to R=2. Has anyone conducted similar experiments? > >Since you didn't specify what engine you have used I assume from your experiment >it was something which didn't do checks in qsearch. > >I think your experiment is of little meaning. > >What data would be interesting here is tree size reduction at different depths >in 'normal' positions; then match result with average depth of 11-14 (this is >low end of what most engines reach at current hw with tournament tc). > >For my engine which does most checks in qsearch R=3 compared to R=2 reduces tree >size by 15-40% at depth=11. It misses some deep, quiet threats comparing to R=2 >(forks, some passed pawn combi, etc), but its WAC result at 5s/position (amd 450 >then) was almost the same (worse by 2 positions if my memory serves). > >In very limited nunn-style matches of 32 games g/15 R=3 was never worse then R=2 >for my engine. > >When engine has stripped down qsearch ala Crafty it will need more depth to >offset additional null reduction. > >Please redo your experiment with fritz which does do checks in qsearch. > >-Andrew- The tree size, etc have been calculated. But that's even not the point. The point is that in practice by changing the R from 2 to 3, the engine won't lose too much strength since on many occasions the faster search by R=3 will find the correct move one ply later but won't waste for that too much. (Although the research wasn't about this point at all, I just found this point interesting). >For my engine which does most checks in qsearch R=3 compared to R=2 reduces >tree size by 15-40% at depth=11. It misses some deep, quiet threats comparing >to R=2 The fixed depth search on test suites shows that R=2 is clearly far stronger than R=3, no surprises there. Of course R=3 misses many tactical threats as you mentioned in fixed depth comparison to R=2.
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