Author: Robert Hyatt
Date: 12:48:48 05/06/04
Go up one level in this thread
On May 06, 2004 at 15:39:15, Dan Honeycutt 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 obviously didn't know it was soft till a short while ago. Inside the window >sounds like "in the comfort zone" or something soft. Outside the window sounds >like "out in the wild" or something hard. I'll remember it easily from now on >since it's simply backwards from what I think it sounds like. > >Dan H. I think the name comes from the idea that the actual alpha/beta window is a "hard" window that bounds the search. You can "soften" the window and return scores outside the initial alpha/beta window if you choose. But if you think of alpha = hard lower bound and beta = hard upper bound, then making them "soft" relaxes them a bit..
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