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Search Results: 1 - 10 of 313 matches for " Akimichi Takemura "
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Exponential decay rate of partial autocorrelation coefficients of ARMA and short-memory processes
Akimichi Takemura
Statistics , 2015,
Abstract: We present a short proof of the fact that the exponential decay rate of partial autocorrelation coefficients of a short-memory process, in particular an ARMA process, is equal to the exponential decay rate of the coefficients of its infinite autoregressive representation.
Goodness-of-Fit Tests for Symmetric Stable Distributions -- Empirical Characteristic Function Approach
Muneya Matsui,Akimichi Takemura
Mathematics , 2006, DOI: 10.1007/s11749-007-0045-y
Abstract: We consider goodness-of-fit tests of symmetric stable distributions based on weighted integrals of the squared distance between the empirical characteristic function of the standardized data and the characteristic function of the standard symmetric stable distribution with the characteristic exponent $\alpha$ estimated from the data. We treat $\alpha$ as an unknown parameter, but for theoretical simplicity we also consider the case that $\alpha$ is fixed. For estimation of parameters and the standardization of data we use maximum likelihood estimator (MLE) and an equivariant integrated squared error estimator (EISE) which minimizes the weighted integral. We derive the asymptotic covariance function of the characteristic function process with parameters estimated by MLE and EISE. For the case of MLE, the eigenvalues of the covariance function are numerically evaluated and asymptotic distribution of the test statistic is obtained using complex integration. Simulation studies show that the asymptotic distribution of the test statistics is very accurate. We also present a formula of the asymptotic covariance function of the characteristic function process with parameters estimated by an efficient estimator for general distributions.
Iterative proportional scaling via decomposable submodels for contingency tables
Yushi Endo,Akimichi Takemura
Mathematics , 2006, DOI: 10.1016/j.csda.2008.11.013
Abstract: We propose iterative proportional scaling (IPS) via decomposable submodels for maximizing likelihood function of a hierarchical model for contingency tables. In ordinary IPS the proportional scaling is performed by cycling through the elements of the generating class of a hierarchical model. We propose to adjust more marginals at each step. This is accomplished by expressing the generating class as a union of decomposable submodels and cycling through the decomposable models. We prove convergence of our proposed procedure, if the amount of scaling is adjusted properly at each step. We also analyze the proposed algorithms around the maximum likelihood estimate (MLE) in detail. Faster convergence of our proposed procedure is illustrated by numerical examples.
Asymptotic Distribution of Wishart Matrix for Block-wise Dispersion of Population Eigenvalues
Yo Sheena,Akimichi Takemura
Mathematics , 2006, DOI: 10.1016/j.jmva.2007.04.001
Abstract: This paper deals with the asymptotic distribution of Wishart matrix and its application to the estimation of the population matrix parameter when the population eigenvalues are block-wise infinitely dispersed. We show that the appropriately normalized eigenvectors and eigenvalues asymptotically generate two Wishart matrices and one normally distributed random matrix, which are mutually independent. For a family of orthogonally equivariant estimators, we calculate the asymptotic risks with respect to the entropy or the quadratic loss function and derive the asymptotically best estimator among the family. We numerically show 1) the convergence in both the distributions and the risks are quick enough for a practical use, 2) the asymptotically best estimator is robust against the deviation of the population eigenvalues from the block-wise infinite dispersion.
Saturation points on faces of a rational polyhedral cone
Akimichi Takemura,Ruriko Yoshida
Mathematics , 2006,
Abstract: Different commutative semigroups may have a common saturation. We consider distinguishing semigroups with a common saturation based on their ``sparsity''. We propose to qualitatively describe sparsity of a semigroup by considering which faces of the corresponding rational polyhedral cone have saturation points. For a commutative semigroup we give a necessary and sufficient condition for determining which faces have saturation points. We also show that we can construct a commutative semigroup with arbitrary consistent patterns of faces with saturation points.
A generalization of the integer linear infeasibility problem
Akimichi Takemura,Ruriko Yoshida
Mathematics , 2006,
Abstract: Does a given system of linear equations with nonnegative constraints have an integer solution? This is a fundamental question in many areas. In statistics this problem arises in data security problems for contingency table data and also is closely related to non-squarefree elements of Markov bases for sampling contingency tables with given marginals. To study a family of systems with no integer solution, we focus on a commutative semigroup generated by a finite subset of $\Z^d$ and its saturation. An element in the difference of the semigroup and its saturation is called a ``hole''. We show the necessary and sufficient conditions for the finiteness of the set of holes. Also we define fundamental holes and saturation points of a commutative semigroup. Then, we show the simultaneous finiteness of the set of holes, the set of non-saturation points, and the set of generators for saturation points. We apply our results to some three- and four-way contingency tables. Then we will discuss the time complexities of our algorithms.
Strong consistency of MLE for finite mixtures of location-scale distributions when the scale parameters are exponentially small (full version)
Kentaro Tanaka,Akimichi Takemura
Mathematics , 2006,
Abstract: In a finite mixture of location-scale distributions maximum likelihood estimator does not exist because of the unboundedness of the likelihood function when the scale parameter of some mixture component approaches zero. In order to study the strong consistency of maximum likelihood estimator, we consider the case that the scale parameters of the component distributions are restricted from below by $c_n$, where $c_n$ is a sequence of positive real numbers which tend to zero as the sample size $n$ increases. We prove that under mild regularity conditions maximum likelihood estimator is strongly consistent if the scale parameters are restricted from below by $c_{n} = \exp(-n^d)$, $0 < d < 1$.
Conditions for swappability of records in a microdata set when some marginals are fixed
Akimichi Takemura,Hisayuki Hara
Mathematics , 2006,
Abstract: We consider swapping of two records in a microdata set for the purpose of disclosure control. We give some necessary and sufficient conditions that some observations can be swapped between two records under the restriction that a given set of marginals are fixed. We also give an algorithm to find another record for swapping if one wants to swap out some observations from a particular record. Our result has a close connection to the construction of Markov bases for contingency tables with given marginals.
Evaluation of per-record identification risk and swappability of records in a microdata set via decomposable models
Akimichi Takemura,Yushi Endo
Mathematics , 2006,
Abstract: We propose a strategy for disclosure risk evaluation and disclosure control of a microdata set based on fitting decomposable models of a multiway contingency table corresponding to the microdata set. By fitting decomposable models, we can evaluate per-record identification (or re-identification) risk of a microdata set. Furthermore we can easily determine swappability of risky records which does not disturb the set of marginals of the decomposable model. Use of decomposable models has been already considered in the existing literature. The contribution of this paper is to propose a systematic strategy to the problem of finding a model with a good fit, identifying risky records under the model, and then applying the swapping procedure to these records.
Integral representations of one dimensional projections for multivariate stable densities
Muneya Matsui,Akimichi Takemura
Mathematics , 2006, DOI: 10.1016/j.jmva.2008.05.007
Abstract: We consider the numerical evaluation of one dimensional projections of general multivariate stable densities introduced by Abdul-Hamid and Nolan (1998). In their approach higher order derivatives of one dimensional densities are used, which seem to be cumbersome in practice. Furthermore there are some difficulties for even dimensions. In order to overcome these difficulties we obtain the explicit finite-interval integral representation of one dimensional projections for all dimensions. For this purpose we utilize the imaginary part of complex integration, whose real part corresponds to the derivative of the one dimensional inversion formula. We also give summaries on relations between various parameterizations of stable multivariate density and its one dimensional projection.
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