Author: Uri Blass
Date: 12:17:39 07/30/02
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On July 30, 2002 at 15:02:25, Tony Werten wrote: >On July 30, 2002 at 13:56:53, Thorsten Czub wrote: > >>in an old program i can set the null move margin on or off. >>what is the function doing ? any ideas or explanations from the programmers? > >I'll give it a guess. > >Normally when you do a nullmove and the score returned is > beta you get a >cutoff. The idea is that if doing nothing already gives bigger than beta, doing >something would give even more. > >You can go one step further with this idea. Since doing something would be >better than doing nothing, then doing nothing doesn't have to be > beta but only >> beta - margin since I expect that a move is worth at least "margin" > >Tony I thought about the opposite. Null move pruning was considered to be a dangerous pruning because you may miss threats and this is probably the reason that programmers like richard lang never used it. If you want to be more careful in pruning you may try to prune only moves when the score after null move is at least beta+margin. Thorsten asked about an old program so it is logical to guess that they tried to reduce the demage by using null move margin. It is possible to find who is right simply by finding if increasing the null move margin help the program to get bigger depth. If increasing the null move margin help the program to get bigger nominal depth then Tony is probably right. Uri
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