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Subject: Re: Double Nullmove

Author: Robert Hyatt

Date: 12:27:26 04/25/02

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On April 25, 2002 at 13:49:42, Dann Corbit wrote:

>On April 25, 2002 at 13:26:43, Robert Hyatt wrote:
>
>>On April 25, 2002 at 12:39:36, J. Wesley Cleveland wrote:
>>
>>>On April 25, 2002 at 02:54:03, Andreas Herrmann wrote:
>>>
>>>>Hi,
>>>>
>>>>I want to implement double nullmove in my chess engine again. Now i'm searching
>>>>for Zugzwang postions, which should be solved by double nullmove instead of
>>>>normal nullmove.
>>>>Another question: How much time costs the double null move in the average.
>>>>I have tested it in some positions, and my engine needs about 30 to 40 percent
>>>>more time for the same search depth. Is that normal or is that to much.
>>>
>>>That seems like far too much. Are you reducing the search depth again for the
>>>second nullmove and only doing it when the first nullmove causes a cutoff? You
>>>might also not want to do it too near the leafs, i.e. if the first nullmove goes
>>>directly into your quiescence search.
>>
>>
>>One simple test... determine how often, in normal positions, the _second_ null-
>>move search fails high.  Whenever it does, the the first null-move search fails
>>low and is useless.  that is probably where the cost is being exposed...
>>
>>In zug positions, the second fail high will cause the first to fail low, which
>>prevents zug problems.  But if it also causes a large number of normal positions
>>to fail this test as well, then it is losing part of the advantage of null-move
>>in general...
>
>I had a notion about double null move --
>
>Implement double null move in the place where normally you will just turn null
>move off [except for check].  Use your regular null move algorithm as always,
>but when conditions indicate null move is not a good idea, switch to double null
>move.


If it was easy to identify positions where a null-move might cause problems,
the problem would already be solved.

:)



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