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Subject: Re: Null move reductions

Author: Robert Hyatt

Date: 20:29:46 10/04/98

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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...

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