Author: Robert Hyatt
Date: 09:00:34 01/29/04
Go up one level in this thread
On January 29, 2004 at 10:26:48, Tony Werten wrote: >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 > Yes. I don't like the term "null-window" as that then gets confused with null-move search which is yet _another_ animal. :) Our CC vocabulary is a bit byzantine at times... >> >> >>> >>>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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