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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Pseudo-random number sampling ： ウィキペディア英語版 Pseudo-random number sampling Pseudo-random number sampling or non-uniform pseudo-random variate generation is the numerical practice of generating pseudo-random numbers that are distributed according to a given probability distribution. Methods of sampling a non-uniform distribution are typically based on the availability of a pseudo-random number generator producing numbers ''X'' that are uniformly distributed. Computational algorithms are then used to manipulate a single random variate, ''X'', or often several such variates, into a new random variate ''Y'' such that these values have the required distribution. Historically, basic methods of pseudo-random number sampling were developed for Monte-Carlo simulations in the Manhattan project; they were first published by John von Neumann in the early 1950s. == Finite discrete distributions == For a discrete probability distribution with a finite number ''n'' of indices at which the probability mass function ''f'' takes non-zero values, the basic sampling algorithm is straightforward. The interval [0, 1) is divided in ''n'' intervals [0, ''f''(1)), [''f''(1), ''f''(1) + ''f''(2)), ... The width of interval ''i'' equals the probability ''f''(''i''). One draws a uniformly distributed pseudo-random number ''X'', and searches for the index ''i'' of the corresponding interval. The so determined ''i'' will have the distribution ''f''(''i''). Formalizing this idea becomes easier by using the cumulative distribution function :$F(i)=\backslash sum\_^i\; f(j).$ It is convenient to set ''F''(0) = 0. The ''n'' intervals are then simply [''F''(0), ''F''(1)), [''F''(1), ''F''(2)), ..., [''F''(''n'' − 1), ''F''(''n'')). The main computational task is then to determine ''i'' for which ''F''(''i'' − 1) ≤ ''X'' < ''F''(''i''). This can be done by different algorithms: * Linear search, computational time linear in ''n''. * Binary search, computational time goes with log ''n''. * Indexed search,〔Ripley (1987) 〕 also called the ''cutpoint method''.〔Fishman (1996) 〕 * Alias method, computational time is constant, using some pre-computed tables. * There are other methods that cost constant time.〔Fishman (1996) 〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Pseudo-random number sampling」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.