Author: Robert Hyatt
Date: 11:32:35 06/16/00
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On June 16, 2000 at 09:43:56, leonid wrote: >Hi! > >Is the number between minimax nodes/second, devided on number of nodes/second >for alpha-beta, equal to around five? > >If, for instance, one position in minimax give 1000000 NPS, the same position >but solved by alpha-beta logic will indicate around 200000 NPS speed? > >Leonid. Speed is not an issue. NPS between alpha/beta and minimax is meaningless. Minimax searches way more nodes than alpha/beta, but it also searches faster because no moves are tossed out by backward pruning. The formula you are looking for is this: for minimax, the total nodes (N) is N = W^D (W=branching factor, roughly 35-38 for chess, D=depth of search). For alpha/beta, the total nodes (N) is N= W^floor(D/2) + W^ceil(D/2) or when D is even N=2*W^(D/2) alpha/beta searches roughly the SQRT(minimax) nodes. Which is significant. In effect, alpha/beta will reach a depth approximately 2x deeper than minimax alone will reach. But NPS really isn't part of the issue, only total nodes searched.
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