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

Author: Robert Hyatt

Date: 07:50:52 07/13/02

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On July 13, 2002 at 02:07:17, Vincent Diepeveen wrote:

>I still do not understand which positions you talk about which R=2
>is finding and R=3 isn't.

Note that he used fixed-depth.   This is therefore not surprising since
some lines will be searched one ply shallower..

>What the hell do you do in qsearch, no checks or so?
>On July 11, 2002 at 17:40:07, Omid David wrote:
>>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.
>>>>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

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