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Subject: Re: Nullmove: when to avoid it?

Author: Miguel A. Ballicora

Date: 11:49:19 02/28/01

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On February 28, 2001 at 13:22:41, Robert Hyatt wrote:

>On February 28, 2001 at 11:10:30, Miguel A. Ballicora wrote:
>
>>On February 28, 2001 at 05:56:36, Leen Ammeraal wrote:
>>
>>>I am not sure about when to avoid nullmoves.
>>>I omit it:
>>>a. when in check
>>>b. when there are less than 5 pieces (including pawns) on the board
>>>c. when the last move was a nullmove
>>>d. at the root node
>>>Should I also omit it in some other cases,
>>>for example, when any hashmove (even with a low draft) was found,
>>>or when beta = alpha + 1?
>>>Thanks in advance for any help.
>>>Leen
>>
>>Hi Leen,
>>
>>Regarding b, I do not know whether what I am doing now is correct but I think
>>that works for me:
>>When either black or white had no "long range" pieces (bishop, rook or queen)
>>I disable null move. The rationale is that one side cannot waste
>>a tempo in a given position having pawns, king and/or knights making the
>>position prone to have a zugswang.
>>
>>Miguel
>
>
>That seems dangerous.  you are white, with a bishop on d5.  I am black and I
>have a pawn on a7 and g7.  The bishop is zugged here.  If your king can't move,
>you lose even though you have a long-range slider on the board.  And null move
>will fail high here naturally as not moving is better than having to move and
>lose.

I think that you meant a3 and g3? If that's so I got your point
and you're right. However, I disable nullmove when _either_ side lacks a
long-range slider. In your example, it will be disabled because you do not
have a bishop. If you do have a bishop, it won't be disabled (both sides got a
slider) but at least I don't have "mutual" zugswangs which are the nastiest (I
think). At least, with a slider per side the mutual zugswangs are more difficult
(of course not impossible but I have to draw a line somewhere).

Regards,
Miguel




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