Author: Gerd Isenberg
Date: 13:19:19 05/06/04
Go up one level in this thread
On May 06, 2004 at 15:47:33, Peter McKenzie wrote: >On May 06, 2004 at 15:23:30, Gerd Isenberg wrote: > >>On May 06, 2004 at 15:05:15, Robert Hyatt wrote: >> >>>On May 06, 2004 at 14:31:08, Gerd Isenberg wrote: >>> >>>>On May 06, 2004 at 11:58:11, Robert Hyatt wrote: >>>> >>>>>On May 06, 2004 at 11:38:44, Dan Honeycutt wrote: >>>>> >>>>>>Yet again I apologize for asking a question which I'm sure has been asked many >>>>>>times before, but could someone explain the difference between a fail-hard and a >>>>>>fail-soft and how does is affect a PVS search? >>>>>> >>>>>>I made the guess that, ie, if (score >= beta) if I return score it's a fail-hard >>>>>>and if I return beta it's a fail-soft. It would seem that what I return doesn't >>>>>>so much matter as what I put in the hash table. If I put in the (possibly) >>>>>>higher value of score then I have a higher lower bound and a greater chance for >>>>>>a hash cut if this position arises again. >>>>>> >>>>>>Thanks in advance. >>>>>>Dan H. >>>>> >>>>>That is backward. But you have the right idea. Fail-hard never returns a value >>>>>outside the initial alpha/beta window. Fail-soft does. >>>> >>>>I often confuse this hard/soft definitions too - i have the wrong mnemonic >>>>trick. Intuitively i found it harder if i jump outside a window ;-) >>> >>> >>>It is just as intuitive as where you store a lower bound but flag the position >>>as an UPPER bound position. Makes sense after a lot of thought, but it still >>>leads to confusion... :) >> >>yes, but that seems more logical to me than the fail-soft versus fail-hard >>issue. To store the lower bound alfa if your score is less or equal to it, hence >>score is an upper bound, it could be lower. >> >>But i never understood why returning values outside the window is soft. > >I'd say that fail-hard is called that because alpha and beta are 'hard' (i.e. >definite) bounds on the score that can be returned. Yep, i got it ;-)
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