Author: Richard Pijl
Date: 03:54:59 01/15/03
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On January 15, 2003 at 06:12:23, David Rasmussen wrote: >Since null moves are illegal in the real game, it is not obvious how it affects >or should affect repetitions and the fifty move rule. >What I do now in Chezzz is just pretty much ignore the relation between these >concepts and formulate them as if they were formulated in isolation. >What is the correct way to deal with these things? >For instance: > >1. What to do with the fifty moves rule counter when doing a null move? I think in situations where you have not done any captures or pawn moves for 30-40 moves nullmove pruning may yield little result as the programs often are 'nullmoving' with real moves anyway. I haven't done experiments with it yet but I seriously consider turning nullmove off when the 50 moves counter reaches 35. But whatever you do, the overall effect in your engine is probably close to zero ... >2. When doing a null move, we obtain a new position, one that can never be > on the board immedeately after the currect position in a real game, but > it is treated as a "normal" position. What if a "repetition" is found of > two of these "imaginary" positions in the current line? We would return a > draw (that is what I do, since I treat these positions as all others, as do > most programs I've seen, Crafty for instance). I think that when you're getting a repetition in search (so it appears twice in search) you can safely return draw. If the first occurrence happens before a nullmove, there is no progress so it probably won't produce a cuttoff as it is likely the repetition (or better) can be reached by not null-moving. Richard. > >I understand the need for draw detection and I understand the benefits of null >move pruning, but I think they affect eachother in an unclear way. What do >others do, and is there a way that is *correct*, and why? > >/David
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