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Algorithmic Lovász local lemma : ウィキペディア英語版 | Algorithmic Lovász local lemma In theoretical computer science, the algorithmic Lovász local lemma gives an algorithmic way of constructing objects that obey a system of constraints with limited dependence. Given a finite set of ''bad'' events in a probability space with limited dependence amongst the ''Ai''s and with specific bounds on their respective probabilities, the Lovász local lemma proves that with non-zero probability all of these events can be avoided. However, the lemma is non-constructive in that it does not provide any insight on ''how'' to avoid the bad events. If the events are determined by a finite collection of mutually independent random variables, a simple Las Vegas algorithm with expected polynomial runtime proposed by Robin Moser and Gábor Tardos〔.〕 can compute an assignment to the random variables such that all events are avoided. ==Review of Lovász local lemma== (詳細はprobabilistic method to prove the existence of certain complex mathematical objects with a set of prescribed features. A typical proof proceeds by operating on the complex object in a random manner and uses the Lovász Local Lemma to bound the probability that any of the features is missing. The absence of a feature is considered a ''bad event'' and if it can be shown that all such bad events can be avoided simultaneously with non-zero probability, the existence follows. The lemma itself reads as follows:
Let be a finite set of events in the probability space Ω. For let denote a subset of such that is independent from the collection of events . If there exists an assignment of reals to the events such that : then the probability of avoiding all events in is positive, in particular :
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「Algorithmic Lovász local lemma」の詳細全文を読む
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