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Subject: Re: NULL MOVE

Author: Will Singleton

Date: 10:49:49 02/24/99

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On February 24, 1999 at 07:44:06, Vincent Diepeveen wrote:

>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.

Yes, just recently I took the alpha update out, since it seemed to be causing
problems on occasion.  I don't know that for certain, but in my case, it's
working better.

Will



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