Author: Vincent Diepeveen
Date: 14:34:53 06/16/05
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On June 16, 2005 at 16:20:38, Dieter Buerssner wrote: >On June 16, 2005 at 05:22:26, Vasik Rajlich wrote: > >>Fail soft helps when you need to re-search, so it helps more in MTD (f) than >>PVS, and doesn't matter at all in pure alpha-beta. > >Vas, fail soft vs. fail hard will change the search tree in "pure alpha-beta". >It will change move ordering. Fail soft has the potential, to give you better >move ordering. Assume some fail low position. Some refutations on ply deeper >mate, others just give the bound back as score, or scores in between. With fail >hard, you may order moves, that are refuted by mate early for the next search >(it needs some luck, to see mate scores, of course). In a later search with >different bounds and fail hard, you may search those moves early (depending on >all the move sorting heurists you use, of course. Yace for example stores a best >move in HT even when failing low). With fail soft, you might start with a more >reasonable move first. > >This also reminds me to the typical move ordering statistics used: "How often do >I fail high in the first move relative to all node I failed high?". In many >positions, (almost) any move will fail high for the current beta. With a higher >beta, only one or a couple may do it. When you picked some stupid move in an >earlier search, instead of one really convincing one, it should be better for >later searches. Though we completely agree with respect to FH and FS, we might also agree upon that the best move doesn't necessarily produce the smallest cutoff-tree. For example already from 1995 and onwards i'm in certain positions carefully avoiding picking the checking move as the first move. It sure might give the biggest cutoff, but it also sure triggers extensions and a huge tactical tree :) Even in 2005 that works brilliantly for move ordering. >Regards, >Dieter
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