Hello, I'm not sure at all. But, in your example, you are assuming that "XX move worths 10 points".
Thats impossible to said without error %. That error could lead the alfa-beta algorithm to prune an important move on a 'bad' board configuration for our evaluation function. Its impossible to decide if a move worths NN points in GO withour error. (that would be the "ultimate" engine by itself). At least with go, with checkers Im sure that the quantity of pieces on the board is good enough as an evaluation function.... but in go .... caos is our friend. --- William Harold Newman <[EMAIL PROTECTED]> escribió: > On Mon, Nov 13, 2006 at 04:25:28PM +0000, Arthur > Cater wrote: > > > > On Monday, November 13, 2006, at 04:02 PM, Eduardo > Sabbatella wrote: > > > > > > > >Using alfa-beta pruning allows you to see more > 'deep' > > >in the game tree. > > > > > >We could say: You exchanges "tree wide view" for > "tree > > >deep view". > > But only by throwing away variations which are > strictly irrelevant to > the result which would be returned by minimax. (See > example described > below.) > > > >Its not soo difficult to miss "the" move, > prunning the > > >tree. > > That is a valid criticism of many approaches which > are called pruning, > but it is not a valid criticism of alpha-beta. > Alpha-beta prunes a > subtree only when it can prove, from inequalities on > earlier search > results, that no possible set of values found in > that subtree can > affect the result returned which would be returned > by minimax. > > > Alpha-beta pruning is "safe", in the sense that it > will find the same > > move as a full > > minimax search. You need to do "aggressive forward > pruning" in order to > > run the > > risk of missing "the" move, but alpha-beta is > conservative not > > aggressive. > > > > You may indeed 'miss "the" move', but when you do, > minimax would do so > > too. > > Yes. > > One way for Eduardo Sabbatella, or anyone else, to > see what's going on > in alpha-beta is to imagine the situation when the > search has already > found that move X is worth 10 points if the opponent > makes his > strongest response. Then, in searching move Y, the > search discovers > that Y is worth only 7 points if the opponent > replies at Z. In > straight minimax, the search will go on to figure > out exactly how many > points Y is worth, looking for moves Z' and Z'' > which bring the value > of Y down to values even lower than 7. In > alpha-beta, the search > algorithm says "even if Z is not the opponent's > strongest refutation, > the possibility of replying with Z is enough to show > that Y is not as > good as X," and prunes the search of all other > variations starting > with Y. > > Such pruning doesn't affect the returned result, > because in effect > straight minimax doesn't really care exactly how > inferior Y is either. > Straight minimax does waste its time figuring out > precisely how > inferior Y is, but the precision of the result > doesn't have any effect > on the ultimate result: no matter what it finds for > Y, minimax > ultimately tells you it is better to move at X for > 10 points, just > like alpha-beta. > _______________________________________________ > computer-go mailing list > [email protected] > http://www.computer-go.org/mailman/listinfo/computer-go/ > __________________________________________________ Correo Yahoo! Espacio para todos tus mensajes, antivirus y antispam ¡gratis! ¡Abrí tu cuenta ya! - http://correo.yahoo.com.ar _______________________________________________ computer-go mailing list [email protected] http://www.computer-go.org/mailman/listinfo/computer-go/
