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

Author: Omid David

Date: 14:40:07 07/11/02

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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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