Author: jonathan Baxter
Date: 17:02:22 11/22/98
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On November 22, 1998 at 19:36:30, Robert Hyatt wrote: >On November 22, 1998 at 18:04:04, jonathan Baxter wrote: > >>Can anyone send me an electronic version of the ICCA article by Hsu on >>Singular Extensions used in DB? >> >>Failing that, can someone give me a quick explanation? I understand >>that they extend moves that look substantially better than all other moves >>at a node. What I don't understand is that given the nature of alpha-beta >>search, often you don't know anything about the value of alternative moves.... >> >>Thanks, >> >>Jon > > >briefly: > >pv-singular move: you search the first move at a node with the normal >window, and the remainder of the moves at that depty with a lowered (offset) >window (alpha-w, beta-w) where w is the singular margin. If all those moves >fail low, the first move is "singular" since it is clearly better. If any >one move fails high, you have to do the original test on the first move to >see if this new best is singular or not... messy but understandable. > >fh-singular move: you search the first move at a node with the normal >window and get a fail high. You first search the *remainder* of the moves >with the offset window, but to reduced depth (say D-2) to see if all of them >still fail low with the offset window. If so, extend. If not, do the same >check as in pv-singular. > >The idea is that at a PV or fail-high node, you try to prove that the best >move is better than all other moves at that ply, by a significant margin. No >"fail-low" node test has been formulated... > >If that isn't clear, feel free to ask more... > It is clear enough, thanks. But doesn't this cost hugely? Searching all remaining nodes at a fail-high node??? Jon >Bob
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