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In the theory of probability for stochastic processes, the reflection principle for a Wiener process states that if the path of a Wiener process ''f''(''t'') reaches a value ''f''(''s'') = ''a'' at time ''t'' = ''s'', then the subsequent path after time ''s'' has the same distribution as the reflection of the subsequent path about the value ''a''. More formally, the reflection principle refers to a lemma concerning the distribution of the supremum of the Wiener process, or Brownian motion. The result relates the distribution of the supremum of Brownian motion up to time ''t'' to the distribution of the process at time ''t''. It is a corollary of the strong Markov property of Brownian motion. ==Statement== If is a Wiener process, and is a threshold (also called a crossing point), then the lemma states: : In a stronger form, the reflection principle says that if is a stopping time then the reflection of the Wiener process starting at , denoted , is also a Wiener process, where: : The stronger form implies the original lemma by choosing . 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「Reflection principle (Wiener process)」の詳細全文を読む スポンサード リンク
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