Computer Chess Club Archives




Subject: Confusion on Null Move

Author: KarinsDad

Date: 17:09:12 02/09/99

I understand the concept of Null move, but I am confused as to why it works so

My confusion lies in the area of piece taking.

In a lot of positions, both sides have moves which will allow a piece to be
taken by the other side. Often, in an equal game, this will not matter as the
side protecting the piece can gain back equal or greater material if the other
side takes the piece.

Since chess programs (as a general rule) play a "reasonable" game of chess (i.e.
they do not hang pieces multiple ply down), then it would seem that at any given
position being checked, that it is the rare case that a 1 ply null move would
not drastically improve the score since regardless of the move being checked,
the best null move will be a piece take that improves the score.

I can understand that in certain positions, improving the score by a single
piece is not sufficient to alter the score enough to prevent a beta cutoff, but
to me (not having the data on hand since my program does not do this yet), it
would seem that this would be a rare case.

Since null move is used by most everyone's program, this assumption would appear
to be false. I was just wondering if someone could explain to me why this is so
and also possibly the multiple cases (and possibly their frequency) of positions
that null move works well on (where it prevents additional searching).

Or is it just a case that null move infrequently helps the search, but when it
does so, it cuts out major chunks of the search tree and not searching (and
calculating moves within) these major chunks makes up for doing multiple
evaluations (and an additional legal move generation) per node?

Thanks in advance,

KarinsDad :)

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