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

Author: Omid David

Date: 15:20:51 07/11/02

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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).
>>>
>>>Uri
>>
>>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.

>
>Note that the alternatives are not only R=2 and R=3
>
>I suspect that starting with a small R in the first iterations may be even
>better.
>
>You can increase R during the search.
>There is no reason to do changes that do programs weaker at blitz on slow
>hardware.
>
>Uri



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