Author: Robert Hyatt
Date: 20:26:23 08/27/04
Go up one level in this thread
On August 27, 2004 at 11:17:35, J. Wesley Cleveland wrote: >On August 26, 2004 at 21:00:10, Robert Hyatt wrote: > >>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. :) > >EGTBs ;) That's not forward pruning. :) Those probes access a perfect tree search all the way to the mate position. Otherwise hash tables would be in the same category..
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