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Subject: Re: Null move reductions

Author: Robert Hyatt

Date: 06:37:31 10/05/98

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On October 05, 1998 at 00:15:01, blass uri 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.
>If this is the case maybe it is better to do null move with R=3  for slower time
>control and maybe even R=4 if you give the computer a very long time
> 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...
>The null move can hide the resulting mate only if there is no threat
>If the evaluation function give bonus for bishop or pawn on f6 or quuen on h6
>when there is a pawn on g6 I do not see how the null move can hide the mate

does it quite easily..  if we are doing a 6 ply search, at ply=3 we find a
way to rip a piece so that the score is +3.00, at ply=4 we try null-move
and subtract an extra two plies from the search depth, which takes us right
to the q-search, where the opponent recaptures the piece, so that the null-
move search fails high.  I don't look at checks in the q-search, which means
my q-search won't see the mate on g7, so we stop the search at ply=3 thinking
that BxN is ok, when our opponent will *really* not play pxB, but will,
instead, play Qg7#.

Next move you see this, but it could be too late...

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