Computer Chess Club Archives




Subject: Re: Nullmove: when to avoid it?

Author: J. Wesley Cleveland

Date: 18:11:01 03/02/01

Go up one level in this thread

On March 02, 2001 at 16:56:11, Severi Salminen wrote:

>>>Yep, that's true. As Bob said it is very rare to have beta=INF. Actually
>>>Beta=INF can occur only in the very beginning of the search until we get our
>>>first real score (score<=INF-Ply). Remember also that you don't have to know
>>>anything else about the nullmove but whether its score is >=beta. So you can
>>>search with (-beta,-beta+1)
>>An idea I had, is that since about half the time we expect a move to fail low,
>>it doesn't make much sense to give the opponent an extra move and expect it to
>>fail high.
>Well, the point is: how do we know it _before_ trying the null move? Futility
>(pre) condition is one good indicator: if(depth==1&&material+MARGIN<=alpha).
We know from where in the search we are, e.g. if the move being considered is
off tje PV, we expect a fail high, and should try nullmove, but the response to
this move should fail low, and nullmove is a waste of time.

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