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Subject: Re: Null move reductions

Author: Roberto Waldteufel

Date: 22:23:56 10/04/98

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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?


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