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This article is supplemental for “Convergence of random variables” and provides proofs for selected results. Several results will be established using the portmanteau lemma: A sequence converges in distribution to ''X'' if and only if any of the following conditions are met:
== Convergence almost surely implies convergence in probability== : Proof: If converges to ''X'' almost surely, it means that the set of points has measure zero; denote this set ''O''. Now fix ε > 0 and consider a sequence of sets : This sequence of sets is decreasing: ''A''''n'' ⊇ ''A''''n''+1 ⊇ ..., and it decreases towards the set : For this decreasing sequence of events, their probabilities are also a decreasing sequence, and it decreases towards the Pr(''A''∞); we shall show now that this number is equal to zero. Now any point ω in the complement of ''O'' is such that lim ''Xn''(ω) = ''X''(ω), which implies that |''Xn''(ω) − ''X''(ω)| < ε for all ''n'' greater than a certain number ''N''. Therefore, for all ''n'' ≥ ''N'' the point ω will not belong to the set ''An'', and consequently it will not belong to ''A''∞. This means that ''A''∞ is disjoint with ''O'', or equivalently, ''A''∞ is a subset of ''O'' and therefore Pr(''A''∞) = 0. Finally, consider : which by definition means that ''Xn'' converges in probability to ''X''. 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「Proofs of convergence of random variables」の詳細全文を読む スポンサード リンク
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