Author: Bert van den Bosch
Date: 11:09:06 08/26/04
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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 :)
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