Author: Dan Honeycutt
Date: 12:32:11 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... :) Are the there known implications on the search from doing using fail-soft vs fail-hard? From a tiny amount of testing it looks like my engine does best using a fail-soft (outside the window) lower-bound (returning beta) and a fail-hard (inside the window) upper-bound (returning alpha). I'm sure I have something backward in that last sentence - see my reply to Anthony below for what I'm trying to determine. Thanks. Dan H.
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