Author: David Rasmussen
Date: 00:59:07 01/22/02
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On January 22, 2002 at 00:44:53, Robert Hyatt wrote: > >What if you run out of time? You failed high on the null-window search. >You started a new search with a wider window and time expired. Do you play >the fail-high move or stick with the previous best move? I stick with the >last verified move. > >Unless I fail high a second time which means the original aspiration window >was too small and I am now going to +infinity. I trust the second fail high >but not the first. > > You are right. I don't take care of that now. Can you tell me where in Crafty this is done? As far as I could see, if you fail high at the root, whether in a null-window search or not, you just return. So maybe some code in iterate.c takes care of this? I couldn't find it though. I couldn't find anything that discriminates between null-windows fail-highs and alpha;beta windows fail-highs. > > >>>2. If you get a fail high at the root on the zero-width window, and when you >>>re-search you get another fail high on the original aspiration window, or you >>>get a true score, then you can trust it. >>> >> >>That's what I'm doing now, I think. >> >>>Case 1 is the killer although it doesn't happen every move, once in a game >>>is more than enough. >> >>I'm sure. >> >>But when I posted, I was really talking about the case where you search with an >>aspiration window, and then you get a fail high with value v. You search with a >>new aspiration windows (in my case [v;MATE]), but then the search turns out to >>find nothing. The fail high was false. How do I avoid that? >> > > >You just take that and go with it. It is easy to see how it can happen, >where a hash entry says "score >= XXX" which will cause a fail high, but >now you can't use that and if you can't see it with a search, you are now >forced to fail low. But the fail high was _right_. > >It is that PVS null-window fail high that can't be trusted at all... > Prelimiary testing shows that aspiration search gives me nothing. If I can confirm this, or if I can find no positions where it really help, I will drop aspiration, and I won't have this kind of error. Also, I wont have to deal with the case above, as beta at the root will always be MATE; /David
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