Author: Vasik Rajlich
Date: 09:53:51 06/19/05
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On June 19, 2005 at 06:44:45, Dieter Buerssner wrote: >On June 18, 2005 at 15:27:32, Vasik Rajlich wrote: > >Thanks for elaborating - I agree with everything. > >>>Lazy eval can be made "soft", futility pruning, too. >>> >> >>As far as I can tell, a lazy eval will always cost you some softness. > >Of course. (Isn't "soft" really anti intuitive - I am no native English speaker, >but I'd imagine the bound gets softer, not harder ...) > >>Regarding futility pruning in q-search, how will you return a good fail-soft >>value here: > >This is not really futility pruning specific, I think > I think of standing pat in q-search as a form of "futility pruning", but I guess that's breaking the official use of the word (going back to the Dark Thought papers ..) >>[D] r1bqk1nr/pppp1ppp/8/2b1p3/3nP3/2NP1N2/PPP1BPPP/R2QK2R w KQkq - 6 1 >> >>White is down a piece and needs to get to +0.50 (that's our window, let's say). >>We'd like q-search to return a fail-soft of -3.00. But: white tries 1. Nxd4, and >>black fails high by standing pat. How do you avoid returning a fail soft of 0.00 >>or so? > >Exactly. Basic qsearch without any tricks will do this by allowing a standpat >score. Perhaps the most important reason, we typically get back fail soft scores >of alpha for all moves at the root besides the PV. > Yes, of the several reasons for bad failing soft, this might be the most common. Maybe MTD (f) engines should disable all "pruning" in the q-search .. Vas >Regards, >Dieter
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