Author: José Carlos
Date: 03:38:36 12/29/99
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On December 28, 1999 at 10:02:23, Robert Hyatt wrote: >On December 28, 1999 at 01:38:49, William Bryant wrote: > >>I looked at this a year ago, but want to again ask the best way to handle >>this situation. >> >>You fail high at the root, >> increase alpha to beta -1 >> increase beta to Mate (or Mate - 1 depending upon how these are defined) >>Then you fail low on the same move. >> >>What I have been doing is accepting the fail high as correct, >> making this the PV move, >> and continuing the search at the next iteration with >> a window set around alpha which is the old beta -1, + or - the aspiration >> window size. >> >>Is this correct, is there a better way to handle a fail high/low. >> >>Thanks >> >>William >>wbryant@ix.netcom.com > > >I have two cases. (don't forget I use PVS). > >1. get a value for first root move as normal, then a later move fails high >on the null-window search, but when I re-search with the normal PVS window, >it now fails low. I pretend the fail high didn't happen and keep the original >root move. > >2. A root move fails high, but then fails low on the re-search. I keep the >fail-high move. You can probably eliminate the fail-low by simply searching >with -inf,+inf, but it will be slower, and due to hash overwrites/draft problems >this fail-high/fail-low problem will happen without this large window. And with >the large window you might fail high on bound X, but get a score back that is >< X... > >It is mainly an artifact of null-move search and hashing... I don't use null-move, but I use hashing, and I don't understand how is it possible to get a fail-high and then a fail-low in the research due to the hashing. As I understand, when I fail-high in the pvs, I get a lower-bound for the real value of the position (I use fail-soft), so if I research with the new alfa set to that value, I could never fail-low. Am I wrong? José C.
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