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Subject: Re: NULL MOVE

Author: Vincent Diepeveen

Date: 04:44:06 02/24/99

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On February 24, 1999 at 02:30:21, Will Singleton wrote:

>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.
>>
>>Thanks.
>>
>>Sylvain.
>
>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.

This is no open question. Of course always do nullmove.
If it doesn't give cutoff then you still can see whether you need a
mating extension.

It saves for me a lot anyway. ALWAYS do nullmove, just take care you
don't improve your alfa with it if it fails. Some do that, but i'm
not a big fan of that.

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



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