Author: Georg v. Zimmermann
Date: 07:36:25 03/10/03
Go up one level in this thread
On March 09, 2003 at 23:15:44, Robert Hyatt wrote: >On March 09, 2003 at 14:39:07, Sune Fischer wrote: >>>>> >>>>>I don't see any reason to extend a move I fail high on, unless there is a threat >>>>>further down. >>> >>>The problem is that often you have _one_ good move. All others fail low, >>>and this _one_ move seems to be good enough and fails high. But if you >>>go deeper, you see it fail also and don't make a mistake. Hence the point >>>for singular-extensions. When you have lots of good moves, if you discover >>>one is bad, that's ok, you have plenty of others. But once you know there >>>is only _one_ good move, it had _better_ be good or the entire path gets >>>mis-evaluated. This is an excellent explanation. I hope one day I can explain that well ,too. The reason you give is the same reason why I like Berliners B* idea so much. Too bad no one got it to work well so far. (more text below) >>Maybe if the fail high margin is too high, don't treat it like a singular move, >>is that what your saying? Maybe this could be made to work, it just makes it >>rather fuzzy what a singular move really is then, having a margin on both sides >>(not non-singular and not over-obviously-singular either!:). > >What you want to know is this: > >For the normal "window", one move is better than beta (this is for the fail >high part, the PV singular is easier to understand) while all the other moves >are much worse. But much worse than the normal beta value, _not_ much worse >than the fail high value itself as it is artificially inflated by hanging a >queen. > >IE if the real expectation for the score is (so far) +1.0, because I have >"won" a pawn, then we hit the critical position with alpha and beta as +1 and >+1.01 or something similar. I try the critical move and get a fail high, and >all others fail badly low as I lose material if I can't play the critical move. >I extend it and search it again. But in the other case, the expected score >might be 0, and the ply after I hang the queen, the alpha/beta values are >still 0,.01 or something similar. PxQ will clearly blow out past beta, but >will all the other moves be worse than -.5 or so? Probably not so we don't >extend. If I mistakenly compare to the alpha value after PxQ, then every >other move might be much worse and trigger the extension and waste time. Basically you suggest to ask "how much worse than PV are all those bad moves?" instead of "how good is this one move compared to all the other options?". That makes sense. It will filter out the "obvious" PxQ cases feared by Sune. But it does depend on bounds, and therefore has the problems you pointed out. Georg
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.