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The Onsager–Machlup function is a function that summarizes the dynamics of a continuous stochastic process. It is used to define a probability density for a stochastic process, and it is similar to the Lagrangian of a dynamical system. It is named after Lars Onsager and S. Machlup who were the first to consider such probability densities.〔Onsager, L. and Machlup, S. (1953)〕 The dynamics of a continuous stochastic process from time to in one dimension, satisfying a stochastic differential equation : where is a Wiener process, can in approximation be described by the probability density function of its value at a finite number of points in time : : where : and , and . A similar approximation is possible for processes in higher dimensions. The approximation is more accurate for smaller time step sizes , but in the limit the probability density function becomes ill defined, one reason being that the product of terms : as , where is the Onsager–Machlup function. ==Definition== Consider a -dimensional Riemannian manifold and a diffusion process on with infinitesimal generator , where is the Laplace–Beltrami operator and is a vector field. For any two smooth curves , : where is the Riemannian distance, denote the first derivatives of , and is called the Onsager–Machlup function. The Onsager–Machlup function is given by〔Takahashi, Y. and Watanabe, S. (1980)〕〔Fujita, T. and Kotani, S. (1982)〕〔Wittich, Olaf〕 : where is the Riemannian norm in the tangent space at , is the divergence of at , and is the scalar curvature at . 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「Onsager–Machlup function」の詳細全文を読む スポンサード リンク
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