Author: Dan Homan
Date: 14:20:34 02/10/99
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On February 10, 1999 at 14:54:43, J. Wesley Cleveland wrote: >On February 09, 1999 at 22:59:52, Robert Hyatt wrote: > >> >> >>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... > >This makes me wonder whether null move is even worthwhile if there is not a >large material difference. I would think that with even material null move would >be much less likely to produce a cutoff and much more likely to give a false >cutoff. This is a very interesting observation. Maybe it would be right to say that null move might be a "waste" of time if the material score is not close to beta? Taken a step further... some kind of a "windowed" null-move might be a good idea. I tried this in my program. I changed my null move code so that a null move would only be tried *only* if the material score for the side to move was greater than (beta-1.5*pawn_value). This reduced my searched nodes from 5-10% in most of the positions I have tried so far. (I have only tried a handful of WAC positions so far.) If this pans out, It is a perfectly safe enhancement to null-move. The 1.5 pawn window that I tried was arbitrary; another value might do better. - Dan
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