Author: Tony Werten
Date: 07:26:48 01/29/04
Go up one level in this thread
On January 29, 2004 at 10:21:11, Robert Hyatt wrote: >On January 29, 2004 at 05:09:30, Tony Werten wrote: > >>On January 28, 2004 at 22:50:05, Robert Hyatt wrote: >> >>> >>>Both are right. >>> >>>Technically, what happens is that it is possible for you to do a very deep >>>search at the root, say when pondering, and you store a hash table entry for >>>position "P" that says score >= .60, depth=15. Now after that long ponder, your >>>opponent plays a different move. Each time you hit position P, you can use that >>>>= .60 score because of the extreme draft stored in the table. And if your >>>current beta value is (say) .3, then you will fail high since the table entry >>>says >= .6. But when you relax beta, and re-search, now when you hit table >>>entry P, you get sufficient draft, but the flag says "LOWER" which means that >>>the .6 value stored is the LOWER bound. That is useless here since our UPPER >>>bound (beta) is +infinity. You can't use it. And you are not searching deep >>>enough to see the reason for the fail high, so now you fail low. >>> >>>That won't cause a problem if you implement it correctly, and the fail high _is_ >>>the correct result for the best move. But you have to take care that the >>>fail-low doesn't cause a re-search when you fail high again. And you have to be >>>sure that you realize that after the fail-high, _that_ is the move you want to >>>play even if it fails low on the re-search. >> >>Really ? I think I disagree. When this happens at the root you don't accept the >>failhigh score, so why would you inside the tree ? > >Different animals. > >If I fail high on the aspiration window at the root, I _know_ that is a valid >fail-high. And I _always_ accept that as the best move no matter _what_ happens >on the re-search. > >If I fail high on the PVS null-window search at the root, it is common to >immediately fail low on the re-search using the original aspiration window. I >ignore that fail high completely as it is often false and caused by a null-move >search failure somewhere below that node. > >I am not quite sure I understood your comment above, however, so maybe I missed >your point "don't accept at root so why accept inside the tree?"..... You might understand it when I tell you that I confused aspiration window with null window :) Tony > > >> >>Tony >> >>> >>>Bruce's case is a pathological problem that will happen. But it is caused by an >>>extreme happening. In a normal search this won't/can't happen (assuming you are >>>not using null-move). But in reality it can. However, 99.9% of the time, >>>re-searching with beta,+infinity after a fail high on alpha,beta will produce a >>>score as expected...
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