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Subject: Re: NULL MOVE

Author: Will Singleton

Date: 23:30:21 02/23/99

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On February 24, 1999 at 01:16:56, Sylvain Lacombe wrote:

>I just finished implementing the null move. At first, i thought it wasn't saving
>much time. Then, i reallize that it does save alot, but only at deeper plys. On
>the first few plys, i think, it evens slow me down. Is that normal? Am i doing
>something wrong?
>I don't use the null move at the first ply, only at the second. It save about
>40% reaching deep 6. But it takes about 10% more for reaching deep 3 and 4.
>Hope, you can help.

You're probably doing something wrong. But get a second opinion. :)

My prog will use about half as many nodes early on, like up to ply 5, then the
effect becomes more pronounced, and in plys above 7 or 8 can show 2-3x
reductions.  But it depends on the position.  If there's a single best move,
there's more reduction than if the position is pretty quiet.  So try it on a
couple of different test suites, like wac vs Bratko-Kopec.  Or, use the
positional BK positions measured against the tactical ones (12 each).

Of course you wouldn't use null on the first ply, that would make it kind of
hard.  Are you using a reduction factor of 2?  That's the most popular, it
seems.  I'm testing R=3 now, seems to work OK.  But stick with 2 to start.

Also, make sure you don't do 2 nulls in a row.  And, for testing purposes, you
should probably limit a null move to one per search (I mean, once the null has
been done, don't do it again below that node).  Then when it's working better,
test out multiple nulls.

Null moves are susceptible to zug positions, so just disable them in the
endgame.  You can try out better things later.

Don't do null when in check!

There's an open question about allowing nulls in the pv, so look at that.  And
make sure to clear the ep flag after a null.

Also, look at what depth you start to disable them.  Try various depths, like 3,
2 and 1.

Hope this helps.


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