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Subject: Re: Null move reductions

Author: Robert Hyatt

Date: 06:32:55 10/05/98

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On October 05, 1998 at 01:23:56, Roberto Waldteufel wrote:

>On October 04, 1998 at 23:29:46, Robert Hyatt wrote:
>>On October 04, 1998 at 21:21:09, Roberto Waldteufel wrote:
>>>On October 04, 1998 at 20:24:08, Will Singleton wrote:
>>>>On October 04, 1998 at 19:06:15, Roberto Waldteufel wrote:
>>>>>Hi all,
>>>>>I wonder what reductions various programs use for the null move. I reduce by two
>>>>>plies, but I believe a one-ply reduction may be more usual. However, I have
>>>>>found R=2 produces quite good results in my program. I would like to hear of
>>>>>others' experiences.
>>>>>Best wishes,
>>>>Amateur uses r=2, and gets about a ply deeper on average.  But I've noticed that
>>>>in positions where there is a clear better move, the node reduction is great,
>>>>and in positions where there is no clear cut better move, the reduction is not
>>>>that great.  Of course, you need it most in the latter situation.  I'm probably
>>>>doing something wrong.  Do you notice anything similar?
>>>Yes, I have noticed more improvement when one move is clearly best than when
>>>there are many plausible candidates, but I had put that down to the nature of
>>>the null move! If there are many plausible moves, then that leaves fewer
>>>terrible moves to cause null-move cutoffs on the next ply. Do you find the same
>>>effect with R=1 as with R=2? I suspect that nodes with a clearly best move are
>>>just plain easier to handle than the rest.
>>>Best wishes,
>>null move, R=2, works well and has been used in crafty for several years
>>now.  But it does cause problems, and definitely won't work if your
>>machine is slow, because depths of 5-6 will crash and burn when you use
>>null-move.  The deeper the search, the safer this becomes, and I haven't
>>seen null-move related losses in a couple of years now.  But early on,I
>>certainly did...  particular in "the" positions like black has castled
>>kingside, played g6, and white gets in Qh6 and bishop/pawn on f6... the
>>null-move can hide the resulting mate...
>I havn't noticed anything like this yet, but I've only been using null move a
>short while, and I did receive a game where Rabbit blundered material in a blitz
>game, but I think this has more to do with the programs poor performance at very
>fast time controls than null move. I'll keep an eye out for any bad side
>effects, but so far I have seen none besides this one case, and my search is
>faster :-) Do you disable null move for blitz, or if you know Crafty is going to
>be competing on slow hardware?

I don't turn it off depending on the speed of the machine, no.  I simply
assume "normal" hardware today.  On the P6, I generally see searches
that go 7-8 plies minimum, which will "hide" the bug quite effectively for
the most part.  If I were seeing 4-5 or maybe even 6 plies, I would have
more problems...

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