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Subject: Re: Nullmove: when to avoid it?

Author: Ricardo Gibert

Date: 14:31:13 02/28/01

Go up one level in this thread

On February 28, 2001 at 16:52:05, Robert Hyatt wrote:

>On February 28, 2001 at 14:49:19, Miguel A. Ballicora wrote:
>>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.
>>>>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.
>>>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
>>I think that you meant a3 and g3?
>Sorry.  I am white, you are black trying to stop both of my pawns.

That still does not work. White can sac one pawn to queen the other. You need to
shift all the units down two ranks to make the intended point (my guess):
[D]8/8/8/P5P1/8/3b4/8/8 w - - 0 0

>> 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).
>That only makes it worse.  So I have a bishop and two pawns threatening to
>promote.  You have the bishop as above.  You are _still_ zugged.  I don't
>see why you would limit null move based on _both_ sides.  You should only
>limit it if the side on move can be zugged.  But in any case, it still fails
>if we both have a bishop.

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