Author: Gerd Isenberg
Date: 12:23:30 05/06/04
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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.
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