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

Author: Omid David

Date: 15:40:24 07/11/02

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On July 11, 2002 at 18:35:04, Uri Blass wrote:

>On July 11, 2002 at 18:20:51, Omid David wrote:
>>On July 11, 2002 at 18:04:37, Uri Blass wrote:
>>>On July 11, 2002 at 17:46:36, Omid David wrote:
>>>>On July 11, 2002 at 17:41:08, Uri Blass 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).
>>>>>This is not the right test.
>>>>>It is clear that if you search to fix depth R=2 is going to be better.
>>>>>The question is what happens when you search for the same time.
>>>>> 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.
>>>>>I think that a better test should include different programs and not the same
>>>>>program against itself.
>>>>>Another point is that R=2 and R=3 are not the only possibilities.
>>>>>>So, apparently R=2 is not _by_far_ better than R=3 as some assume.
>>>>>I suspect that it is dependent on the program(results may be different for
>>>>>programs with different qsearch and different evaluation).
>>>>I don't expect R=2 to gain more from greater speed than R=3. As a matter of fact
>>>>as Dr.Hyatt recently mentioned with faster hardware in the future, R=3 might
>>>>reach depths in which the total saving would be more significant than tactical
>>>>deficiency (deeper search would compensate for it). In such cases one might even
>>>>think of R=4 at some parts of the search tree (or as Dr.Hyatt just mentioned an
>>>>adaptive R=3~4 value).
>>>I agree that R=3 and R=4 should be also considered.
>>>From my experience in GCP test suites at 5 minutes per move recursive R=3 got
>>>the best results so far in GCP test suites(I do not know about games because I
>>>did not test it for games at slow time control but I suspect that it is possible
>>>that for movei R=3 may be even better than R=2 at the same time control).
>>I think in blitz time controls R=2 will be by far stronger than R=3, since the
>>search won't get deep enough and consequently:
>>1. R=3 won't save too much search effort in comparison to R=2
>>2. R=3 won't have time to search deeper to compensate its tactical deficiencies.
>>But in deeper time controls especially in faster engines like Crafty, it'll
>>perform better I believe.
>1)Crafty is not using R=3 but R=2/3 so comparison between R=3 and R=2 is not
>relevant for crafty.

But you can set a fixed R-value by setting the MAX and MIN to the same value. It
might be interesting to conduct Crafty self-play with R=2 vs. R=3.

>2)Crafty is not doing checks in the first plies of the qsearch and I guess that
>the result is bigger advantage for R=2 in blitz.

While working on test suites I delibertely turn off checks in qsearch, to get
better distinction between different R-values.

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