Author: Robert Hyatt
Date: 21:49:38 03/08/03
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On March 06, 2003 at 08:27:26, Georg v. Zimmermann 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. > >What you describe happens ALL the time. > >>In that case I would prefer a heuristic that extends on threats >>directly. > >For that heuristic to work, you will have to see that its a threat. Often you >will have looked deep enough for the singular extensions to kick in, but without >seeing the threat. > >>Extending singular moves like PxQ where there is no threat involved is a waste >>of time as far as I can tell. You can avoide such extensions pretty easily. IE gross winning captures don't need to be extended most of the time. Ditto for recaptures. > >In the case of 1.e4 e5 2.Qh5 d6 3. Qxe5 //dxe5// : agreed. >But how about 1. e4 e5 2. Qf3 Qf6 3.Qxf6 //gxf6// ? > >To distinguish between those 2 cases all tactically strong engines I know of use >extensions depending on bounds (alpha/beta). > >Georg using bounds introduces yet another set of problems. change the bound, you change the extensions that trigger, and you see fail highs followed by fail lows on the re-search, etc.
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