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Subject: Re: Null-Move: Difference between R = 2 and R = 3 in action

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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