# Pathwise integration and change of variable formulas for continuous paths with arbitrary regularity

Abstract : We construct a pathwise integration theory, associated with a change of variable formula , for smooth functionals of continuous paths with arbitrary regularity defined in terms of the notion of p-th variation along a sequence of time partitions. For paths with finite p-th variation along a sequence of time partitions, we derive a change of variable formula for p times continuously differentiable functions and show pointwise convergence of appropriately defined compensated Riemann sums. Results for functions are extended to regular path-dependent functionals using the concept of vertical derivative of a functional. We show that the pathwise integral satisfies an 'isometry' formula in terms of p-th order variation and obtain a 'signal plus noise' decomposition for regular functionals of paths with strictly increasing p-th variation. For less regular functions we obtain a Tanaka-type change of variable formula using an appropriately defined notion of local time. These results extend to multidimensional paths and yield a natural higher-order extension of the concept of 'reduced rough path'. We show that, while our integral coincides with a rough-path integral for a certain rough path, its construction is canonical and does not involve the specification of any rough-path superstructure.
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https://hal.archives-ouvertes.fr/hal-01742614
Contributor : Rama Cont <>
Submitted on : Wednesday, March 28, 2018 - 9:18:22 PM
Last modification on : Monday, June 15, 2020 - 12:00:34 PM

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Rama Cont, Nicolas Perkowski. Pathwise integration and change of variable formulas for continuous paths with arbitrary regularity. Transactions of the American Mathematical Society, American Mathematical Society, 2019, 6 (161-186), ⟨10.1090/btran/34⟩. ⟨hal-01742614v2⟩

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