Author: Bo Persson
Date: 10:33:54 01/19/05
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On January 18, 2005 at 09:44:29, S J J wrote: > > I have a very novice program working without an alpha beta search. On the >surface, it looks like an alpha-beta search can miss a good sacrifice move. Yes, and no. > > It does may sense that an alpha-beta search will help speed the evaluation >of a tree of, say, 6 ply. It helps in that an alpha-beta searxh (with a good move ordering) will reach 6 plies in about the same time a minimax search reaches 3 plies. That has solved the problem of good moves at plies 4, 5, and 6. :-) > > However, if there is a sacrifice on the sixth ply that does not gain >the material back until, for example, the 8th ply, won't the node be trimmed >when the sixth ply is evaluated and never have additional moves from that >node generated? That's the next problem. :-) One solution to this is, of course, to not stop searching. You can continue a limited search for positions where captures are imminent, playing out the captures and recaptures until the position is more quiet. This is usually called a quiescence search. If you extend carefully, and in important positions, you will see more good moves. If you extend too much, it will take so much time that you will never reach ply 6 at all... Bo Persson
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