局部完全对称的亚半正定矩阵的行列式的不等式

本文得到一个局部完全对称的亚半正定矩阵的行列式的不等式，拓广了[2，3]的结果．     

一类区间自映射拓扑共轭的充要条件

本文给出了线段自映射的共轭与其“值特征矩阵”的关系，本文的结果是相应于文[1]～[5]的推广.     

Acceleration of the EM Algorithm by using Quasi-Newton Methods

The EM algorithm is a popular method for maximum likelihood estimation. Its simplicity in many applications and desirable convergence properties make it very attractive. Its sometimes slow convergence, however, has prompted researchers to propose methods to accelerate it. We review these methods, classifying them into three groups: pure , hybrid and EM-type accelerators. We propose a new pure and a new hybrid accelerator both based on quasi-Newton methods and numerically compare these and two other quasi-Newton accelerators. For this we use examples in each of three areas: Poisson mixtures, the estimation of covariance from incomplete data and multivariate normal mixtures. In these comparisons, the new hybrid accelerator was fastest on most of the examples and often dramatically so. In some cases it accelerated the EM algorithm by factors of over 100. The new pure accelerator is very simple to implement and competed well with the other accelerators. It accelerated the EM algorithm in some cases by factors of over 50. To obtain standard errors, we propose to approximate the inverse of the observed information matrix by using auxiliary output from the new hybrid accelerator. A numerical evaluation of these approximations indicates that they may be useful at least for exploratory purposes.     

亚半正定矩阵的两个等价条件

指出了已有文献中两个重要定理的错误，并给出了修正结果，同时给出了亚正定矩阵的合同标准型及亚半正定矩阵两个等价条件．     

Multivariate Stochastic Volatility Models with Correlated Errors

We develop a Bayesian approach for parsimoniously estimating the correlation structure of the errors in a multivariate stochastic volatility model. Since the number of parameters in the joint correlation matrix of the return and volatility errors is potentially very large, we impose a prior that allows the off-diagonal elements of the inverse of the correlation matrix to be identically zero. The model is estimated using a Markov chain simulation method that samples from the posterior distribution of the volatilities and parameters. We illustrate the approach using both simulated and real examples. In the real examples, the method is applied to equities at three levels of aggregation: returns for firms within the same industry, returns for different industries, and returns aggregated at the index level. We find pronounced correlation effects only at the highest level of aggregation.     

Correspondence analysis of square asymmetric matrices

The application of correspondence analysis to square asymmetric tables is often unsuccessful because of the strong role played by the diagonal entries of the matrix, obscuring the data off the diagonal. A simple modification of the centring of the matrix, coupled with the corresponding change in row and column masses and row and column metrics, allows the table to be decomposed into symmetric and skew symmetric components, which can then be analysed separately. The symmetric and skew symmetric analyses can be performed by using a simple correspondence analysis program if the data are set up in a special block format. The methodology is demonstrated on a social mobility table from the first democratically elected Parliament in Germany, the Frankfurter Nationalversammlung . The table cross-tabulates the jobs of parliamentarians when first entering the labour market and their jobs in May 1848 when the Parliament started its first session.     

有限导电圆柱散射极化特性分析

利用极化理论和高频方法对有限长理想导电圆柱后向散射场的极化特性进行分析和计算。给出了目标极化散射矩阵，不同方向角、不同极化入射波的雷达散射截面及其数值结果。理论分析和数值结果对雷达目标极化检测与识别、隐身与反隐身等信息传输技术有参考价值。     

一类广义RA码的优化设计方法

由重复器、交织器、组合器和广义累加器组成的广义系统RA码,采用低密度奇偶校验码(LDPC码)的置信传播译码时,码性能受稀疏校验矩阵的小环影响大,而稀疏校验矩阵由编码器的结构决定。该文根据置信传播译码的无环要求,通过重复器、交织器、组合器和广义累加器的联合优化设计,给出了无4环的广义RA码的奇偶校验矩阵设计方法。研究结果显示,该方法实现简单,实用性强,设计的广义RA码编码增益大。     

Structural adjustment and family policy in Africa: Lessons from Sudan

The economic strategy pursued by a country profoundly influences the well-being of families. This article uses a social accounting model of the Sudanese economy to compare the effects of two alternative development strategies on growth, employment, and income distribution. The first strategy considered is a conventional growth-oriented strategy emphasizing irrigated, export-oriented agriculture and modern, capital-intensive industry; the second one is a traditional agriculture-led development (TALD) strategy focused on enhancing equity and improving family nutrition by expanding food production. The study's findings for Sudan demonstrate that there is no necessary trade-off between growth and equity. The TALD strategy fosters income growth for the most vulnerable families while simultaneously maximizing aggregate growth. It also holds the prospect of enhancing family equity and increasing access to traditional institutions that provide support to families.World BankHer research interests encompass issues related to poverty and inequality in developing countries. She received her Ph.D. from Cornell University.Before joining the World Bank, he was a visiting scholar at the University of Connecticut and acting head of the Department of Econometrics, University of Khartoum, Khartoum, Sudan. His research interests span development economics (growth, poverty, and equity), public finance, and economic transition in Eastern Europe. He received his Ph.D. from the University of Pittsburgh.     

综合性物流企业信息系统集成度研究

本文从综合物流企业信息系统集成的角度出发,将集成部的定义引入,利用矩阵原理将复杂物流系统整体结构分解为多级递阶的等级结构,分析了各个信息系统之间的集成程度.仓储、海运、陆运、空运、快递业务管理信息系统之间是有循环存在的强联结关系,安全和客户管理信息系统是物流管理信息系统的最高级,外部资源辅助管理系统和呼叫中心处在同一级,财务管理信息系统位于第2级,人力资源管理信息系统位于最低一级.