Author: Robert Hyatt
Date: 18:00:10 08/26/04
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On August 26, 2004 at 14:09:06, Bert van den Bosch wrote: >On August 26, 2004 at 11:33:48, Robert Hyatt wrote: > >>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. :) > >alphabeta :) OK. If you want an error-free _forward-pruning_ algorithm, good luck. Logic says no such thing exists. :)
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