检索结果-南通市图书馆

Relationship of causal effects in a causal chain and related inference

在线全文

学校读者我要写书评

暂无评论

Science China Mathematics 2004年第5期47卷 730-740页

作者： GENG Zhi HE Yangbo WANG Xueli School of Mathematical Sciences LMAM Peking University Beijing 100871 China School of Mathematical Sciences LMAM Peking University Beijing 100871 China School of Mathematical Sciences LMAM Peking University Beijing 100871 China

This paper discusses the relationship among the total causal effect and local causal effects in a causal chain and identifiability of causal effects. We show a transmission relationship of causal effects in a causal chain. According to the relationship, we give an approach to eliminating confounding bias through controlling for intermediate variables in a causal chain.

关键词： causal chain, causal inference, counterfactual model, graphical model, potential causal function.

On cutting sequences of the L-shaped translation surface tiled by three squares

在线全文

学校读者我要写书评

暂无评论

Science China Mathematics 2015年第6期58卷 1311-1326页

作者： WU ShengJian ZHONG YuMin lmam and School of Mathematical Sciences Peking University

We consider a symbolic coding of bi-infinite non periodic geodesics on the L-shaped translation surface tiled by three squares. Each bi-infinite non periodic geodesic is associated with a cutting sequence corresponding to the sequence of labeled saddle connections hit. We prove that there is a relationship between the cutting sequences and the actions of some affine automorphisms of the translation surface. We also get an explicit formula to determine the direction of a bi-infinite non periodic geodesic by using the corresponding cutting sequence.

关键词： affine shaped cutting labeled intersection letter infinite compatible saddle explicit

The computation of Buehler confidence limits

在线全文

学校读者我要写书评

暂无评论

Science China Mathematics 2005年第8期48卷 1065-1074页

作者： FANG Xiangzhong CHEN Jiading School of Mathematical Science LMAM Peking University Beijing 100871 China School of Mathematical Science LMAM Peking University Beijing 100871 China

In medicine and industry, small sample size often arises owing to the high test cost. Then exact confidence inference is important. Buehler confidence limit is a kind of exact confidence limit for the function of parameters in a model. It can be always defined if the order in sample space is given. But the computing problem is often difficult, especially for the cases with high dimension parameter or with incomplete data. This paper presents an algorithm to compute the Buehler confidence limits by EM algorithm. This is the firsttime usage of EM algorithm on Buehler confidence limits, but the algorithm is often used for maximum likelihood estimate in literatures. Three computation examples are given to illustrate the method.

关键词： Buehler confidence limits, EM algorithm, small sample.

ENTROPY PRODUCTION RATE OF THE MINIMAL DIFFUSION PROCESS

在线全文

学校读者我要写书评

暂无评论

Acta Mathematica Scientia 2007年第1期27卷 145-152页

作者：章复熹钱敏 lmam School of Mathematical Sciences Peking University

The entropy production rate of stationary minimal diffusion processes with smooth coefficients is calculated. As a byproduct, the continuity of paths of the minimal diffusion processes is discussed, and that the point... 详细信息

关键词： Minimal diffusion process entropy production rate continuous path

Cheeger's cut, maxcut and the spectral theory of1-Laplacian on graphs

在线全文

学校读者我要写书评

暂无评论

Science China Mathematics 2017年第11期60卷 1963-1980页

作者： CHANG KungChing SHAO SiHong ZHANG Dong lmam and School of Mathematical Sciences Peking University

This is primarily an expository paper surveying up-to-date known results on the spectral theory of1-Laplacian on graphs and its applications to the Cheeger cut, maxcut and multi-cut problems. The structure of eigenspa... 详细信息

关键词： spectral graph theory Laplacian graph cut optimization critical point theory

Algorithm for phase contrast X-ray tomography based on nonlinear phase retrieval

在线全文

学校读者我要写书评

暂无评论

Applied Mathematics and Mechanics(English Edition) 2008年第1期29卷 101-112页

作者：倪文磊周铁 lmam School of Mathematical SciencesPeking University

A new algorithm for phase contrast X-ray tomography under holographic measurement was proposed in this paper. The main idea of the algorithm was to solve the nonlinear phase retrieval problem using the Newton iterative method. The linear equations for the Newton directions were proved to be ill-posed and the regularized solutions were obtained by the conjugate gradient method. Some numerical experiments with computer simulated data were presented. The efficiency, feasibility and the numerical stability of the algorithm were illustrated by the numerical experiments. Compared with the results produced by the linearized phase retrieval algorithm, we can see that the new algorithm is not limited to be only efficient for the data measured in the near-field of the Fresnel region and thus it has a broader validity range.

关键词： phase contrast tomography holographic measurement phase retrieval

On tail behavior of nonlinear autoregressive functional conditional heteroscedastic model with heavy-tailed innovations

在线全文

学校读者我要写书评

暂无评论

Science China Mathematics 2005年第9期48卷 1169-1181页

作者： PAN Jiazhu WU Guangxu lmam and School of Mathematical Sciences Peking University Beijing 100871 China LMAM and School of Mathematical Sciences Peking University Beijing 100871 China

We study the tail probability of the stationary distribution of nonparametric nonlinear autoregressive functional conditional heteroscedastic (NARFCH) model with heavytailed innovations. Our result shows that the tail of the stationary marginal distribution of an NARFCH series is heavily dependent on its conditional variance. When the innovations are heavy-tailed, the tail of the stationary marginal distribution of the series will become heavier or thinner than that of its innovations. We give some specific formulas to show how the increment or decrement of tail heaviness depends on the assumption on the conditional variance function. Some examples are given.

关键词： tail probability, stationary distribution, nonlinear AR model, nonlinear autoregressive functional conditional heteroscedastic model, heavy-tailed distribution.

Equivalence of three kinds of well-posed-ness of discontinuous Riemann-Hilbert problem for elliptic complex equation in multiply connected domains

在线全文

学校读者我要写书评

暂无评论

Applied Mathematics(A Journal of Chinese Universities) 2014年第2期29卷 183-193页

作者： WEN Guo-chun lmam School of Mathematical Sciences Peking University

In this article, we first introduce the general linear elliptic complex equation of first order with certain conditions, and then propose discontinuous Riemann-Hilbert problem and some kinds of modified well-posed-ness for the complex equation. Then we verify the equivalence of three kinds of well-posed-ness. The discontinuous boundary value problem possesses many applications in mechanics and physics etc.

关键词： Discontinuous Riemann-Hilbert problems linear elliptic complex equation equivalence of threekinds of well-posed-ness multiply connected domains.

A ROBUST FINITE ELEMENT METHOD FOR A 3-D ELLIPTIC SINGULAR PERTURBATION PROBLEM

在线全文

学校读者我要写书评

暂无评论

Journal of Computational Mathematics 2007年第6期25卷 631-644页

作者： Ming Wang Xiangrui Meng lmam School of Mathematical Science Peking University Beijing 100871 China

This paper proposes a robust finite element method for a three-dimensional fourth-order elliptic singular perturbation problem. The method uses the three-dimensional Morley element and replaces the finite element functions in the part of bilinear form corresponding to the second-order differential operator by a suitable approximation. To give such an approximation, a convergent nonconforming element for the second-order problem is constructed. It is shown that the method converges uniformly in the perturbation parameter.

关键词： Finite element Singular perturbation problem.