Author: Ernst A. Heinz
Date: 08:01:30 08/28/00
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Hi Dan, >One scheme I read about (in one of Levy's books I think) involved just >continuing on when you get a fail-high, and searching all the rest of the >moves--unless you get a second fail-high. Then the question becomes "which >of the two fail-high moves is the best?" I don't recall exactly how you >proceed after this, but you don't need to re-search any of the other moves >that have already been searched that didn't fail-high. You do have to >re-search the two fail-highs, however. I guess this scheme isn't very good >for PVS search since you might end up without a PV to follow. In "DarkThought" I have refined this technique of "lazy alpha bounding" at the top level quite a bit for searching root moves. My article "How DarkThought Plays Chess" in the ICCA Journal 20(3), pp. 166-176, Sept. 1997 (http://supertech.lcs.mit.edu/~heinz/dt/) and my book on "Scalable Search in Computer Chess" (http://supertech.lcs.mit.edu/~heinz/node1.html) give the following brief explanation. ``At the top level, "DarkThought" employs lazy alpha bounding and iterative deepening with an aspiration window of half a Pawn [127,191]. In contrast to plain alpha bounding [182], the lazy scheme delays the complete resolution of both new best moves and fail highs up to the next iteration. Top-level alpha bounding often saves some effort while at the same time searching new best moves one ply deeper than usual. If the top-level search is unstable or if the final score lies far below the score of the previous move, "DarkThought" extends the duration of the current search up to threefold when playing in tournament mode.'' Cheers, =Ernst=
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