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

Author: Uri Blass

Date: 15:04:37 07/11/02

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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).

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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