Author: Omid David
Date: 14:40:07 07/11/02
Go up one level in this thread
On July 11, 2002 at 17:37:37, Robert Hyatt wrote: >On July 11, 2002 at 17:27:50, Omid David wrote: > >>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. > > >I think this last should be expected. But the point should be that R=3 should >actually go deeper, maybe a ply. Which _might_ gain back the tactical losses >found at equal depths. Yes, this is the only explanation why while R=2 is far stronger than R=3 in fixed depth, in practical matches R=2 doesn't have such a great dominance over R=3.
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