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In mathematical analysis, the Russo–Vallois integral is an extension to stochastic processes of the classical Riemann–Stieltjes integral : for suitable functions and . The idea is to replace the derivative by the difference quotient : and to pull the limit out of the integral. In addition one changes the type of convergence. ==Definitions== Definition: A sequence of stochastic processes converges uniformly on compact sets in probability to a process : if, for every and : One sets: : : and : Definition: The forward integral is defined as the ucp-limit of :: Definition: The backward integral is defined as the ucp-limit of :: Definition: The generalized bracket is defined as the ucp-limit of :: For continuous semimartingales and a cadlag function H, the Russo–Vallois integral coincidences with the usual Ito integral: : In this case the generalised bracket is equal to the classical covariation. In the special case, this means that the process : is equal to the quadratic variation process. Also for the Russo-Vallois Integral an Ito formula holds: If is a continuous semimartingale and : then : By a duality result of Triebel one can provide optimal classes of Besov spaces, where the Russo–Vallois integral can be defined. The norm in the Besov space : is given by : with the well known modification for . Then the following theorem holds: Theorem: Suppose : : : Then the Russo–Vallois integral : exists and for some constant one has : Notice that in this case the Russo–Vallois integral coincides with the Riemann–Stieltjes integral and with the Young integral for functions with finite p-variation. 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「Russo–Vallois integral」の詳細全文を読む スポンサード リンク
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