Author: Robert Hyatt
Date: 08:33:48 08/26/04
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On August 25, 2004 at 17:37:59, Bert van den Bosch wrote: >First of all, I hope the forum will continue in some way! > >Before it is gone, I have a question. > >I wanted to check my null move so I tested if the null move would create a >cutoff, and after that I did the normal stuff. So if you have a cutoff with null >moving you are almost sure you will also get a cutoff with the normal proces, >except for zugzwangs of course. But this wasn't happening all the time when I >tested it, and usually the values involved from what I got back from nullmove >and from the normal process were just a few centipawns in difference. Could this >be because of search instabillity? If it isn't a bug in my program I had the >idea to search nullmove with beta-MARGIN in order for the value returned by null >move to bridge the few centipawns gap. And taking MARGIN the few centipawns. But >I'm not sure if that is correct. Can someone shine a light on this? > >Thanks, greetings Bert This isn't what null-move is about. It will fail high in positions where a normal search won't, but that doesn't make it wrong. The point is that if your opponent can move twice in a row and you fail high after "passing" then your position is very good and it is safe to avoid searching to the normal depth to see if it is even better. As a general rule, if null-move fails high, a normal search should also fail high, of course, as that is the point in that the null-move search is easier to do since it searches to a reduced depth. But there is nothing to say that if the null-move search fails high that the regular search will not, that is part of the risk you take, since null-move is not 100% accurate. Reduce the depth and you obviously will miss some tactical shots that the deeper depth would not miss. If you want an "error-free" pruning algorithm, good luck. Logic says no such thing exists. :)
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