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

Author: Vincent Diepeveen

Date: 16:00:12 07/12/02

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On July 11, 2002 at 16:38:50, Omid David wrote:

I use R=3 always. DIEP searches a ply deeper with it versus combining
it with R=2 not to mention doing R=2 always. In your
tactical testsets you should give IMHO the R=3 program a ply more.

I can imagine programs that do all kind of dubious things to need less
nodes/systemtime a ply (forward pruning, futility pruning, lazy evaluation),
that they can do with R=2.

>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?

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