Author: Robert Hyatt
Date: 19:59:52 02/09/99
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On February 09, 1999 at 20:09:12, KarinsDad wrote: >I understand the concept of Null move, but I am confused as to why it works so >well. > >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, > one of the big 'time savers' is what happens _below_ a sacrifice for nothing. Qxp pxq. And now no matter what two moves white plays in a row, black's position is still 'good' and everything below such moves gets trimmed away instantly... IE with a full-width search, there are _many_ captures that are losers. Null move reduces the depth below these moves and make dismissing them quick and easy... >KarinsDad :)
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