arXiv subjects

Hayate Yamagishi

Publications and source records attributed to Hayate Yamagishi.

4 recordsLinked to original sources

arXiv2024

Asymptotic expansion of the weighted power variation with second order differences of a stochastic differential equation driven by fBm

We study a process satisfying a one-dimensional stochastic differential equation driven by fractional Brownian motion with Hurst index $H>1/2$, and consider the weighted power variation based on the second order differences of the process. We derive the asymptotic expansion formula of its distribution based on the theory of expansion of Skorohod integrals by Nualart and Yoshida. The formula includes the rate of convergence as a corollary. To facilitate the application of the general expansion theory, we employ the theory of exponents from arXiv:2407.02254 to obtain estimates of functionals.

math.PR↗

arXiv2024

Asymptotic expansion of a Hurst index estimator for a stochastic differential equation driven by fBm

We study the asymptotic properties of an estimator of Hurst parameter of a stochastic differential equation driven by a fractional Brownian motion with $H > 1/2$. Utilizing the theory of asymptotic expansion of Skorohod integrals introduced by Nualart and Yoshida [NY19], we derive an asymptotic expansion formula of the distribution of the estimator. As an corollary, we also obtain a mixed central limit theorem for the statistic, indicating that the rate of convergence is $n^{-\frac12}$, which improves the results in the previous literature. To handle second-order quadratic variations appearing in the estimator, a theory of exponent has been developed based on weighted graphs to estimate asymptotic orders of norms of functionals involved.

math.PR↗

arXiv2022

Asymptotic expansion of an estimator for the Hurst coefficient

Asymptotic expansion is presented for an estimator of the Hurst coefficient of a fractional Brownian motion. For this, a recently developed theory of asymptotic expansion of the distribution of Wiener functionals is applied. The effects of the asymptotic expansion are demonstrated by numerical studies.

math.ST↗

arXiv2022

Order estimate of functionals related to fractional Brownian motion and asymptotic expansion of the quadratic variation of fractional stochastic differential equation

We derive an asymptotic expansion for the quadratic variation of a stochastic process satisfying a stochastic differential equation driven by a fractional Brownian motion, based on the theory of asymptotic expansion of Skorohod integrals converging to a mixed normal limit. In order to apply the general theory, it is necessary to estimate functionals that are a randomly weighted sum of products of multiple integrals of the fractional Brownian motion, in expanding the quadratic variation and identifying the limit random symbols. To overcome the difficulty, we introduce two types of exponents by means of the "weighted graphs" capturing the structure of the sum in the functional, and investigate how the exponents change by the action of the Malliavin derivative and its projection.

math.PR↗