Author: Slater Wold
Date: 12:10:15 02/05/04
Go up one level in this thread
On February 05, 2004 at 15:01:13, Bob Durrett wrote: >>>Obviously with bad move ordering, Alpha/Beta resorts back to M-M, which is >>>exactly what A/B is trying to avoid. >>> >>>But what I think Bob D. is wondering, is that Alpha/Beta seems to be tailored >>>simple material returns. I think he is worried that a huge positional eval >>>would be hindered by bad returns from A/B. >>> >>>A/B works from your search, not your eval. >>> >>>I think his questions is, can they get in the way of each other? >> >> >>as I mentioned, alpha/beta is order dependent. Get the order wrong and the tree >>size blows up. So the correct question to ask is "can your move order code >>accurately predict moves that lead to the best evaluation score?" For example, >>in a material-only search, looking at winning (SEE) captures first tends to do >>exactly what you want... > >So, in modern engines, what are the determining factors which set the move >ordering? What does choice of move ordering depend on and what does it not >depend on? > >Bob D. Move ordering is done by your search, which is done by your move generator. Of course, you can always add +/- to a move, based on what it does (captures, checks, advances, etc.). Your move ordering has to 'compliment' your eval. In other words, if you spit out random moves in your move ordering, there is a good chance that crap moves are going to be in the top. When A/B comes along, it will blow up your search tree and slow your engine down, cause you've now resorted back to a Min-Max search. But if your move ordering compliments your eval, then the first move or two, will return a cutoff, and you will get a better branching factor, resulting in more ply.
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