随机变量概念引入的教学探讨

分析引入随机变量概念的步骤和随机变量概念产生的意义,提出从以下四个方面来引入和支持随机变量概念的学习：一是用数来表示事件;二是对比表示事件的两种方法,显示数量表示方法的优越性;三是随机变量概念的提出使概率研究从个别概率问题计算拓展为随机变量的分布规律研究;四是随机变量概念的提出使分析工具得以运用.     

User preference mining based on fine-grained sentiment analysis

User preference mining is an application of data mining that attracts increasing attention. Although most of the existing user preference mining methods achieved significant performance improvement, the sentiment tendencies of users were seldom considered. This paper proposes fine-grained sentiment analysis for preference mining. The powerful feature representation capabilities of deep neural networks have significantly improved the performance of fine-grained sentiment analysis. But two main challenges remain when using deep neural network models: incomplete user feature extraction and insufficient interaction. In response, a pre-training language model is employed to encode user features to fully explore potential interests of users, a linguistic knowledge model is introduced to assist the encoding, a multi-scale convolution neural network is adopted to capture text features at different scales and fully utilize the text information, and the fine-grained sentiment analysis task is modeled as a sequence labeling problem to explore the sentiment polarity of user evaluation. Experiments on a user review data set are used to verify the new approach. Experimental results of precision, recall rate and F1-value show that the proposed approach performs better, and is more effective than baseline models. For example, the F1-value is increased by 4.27% compared to the best performing baseline model. Findings have important implications for research and practice.     

不确定条件下缺货不补货的库存模型分析

对以前研究得很少的一种情况——连续检查库存、提前期固定、需求随机且缺货不补进行了分析,详细推导了其最佳订货点和订货批量,并探讨了简化计算的合理性,然后用EXCEL进行了实例计算,最后进一步推广到提前期也随机的情况。     

Pearson type VII ratio distribution

In modern decision-making processes, ratios or indices of stochastic variables are commonly used criteria. The decision criterion is, however, frequently presented as deterministic despite the fact that sampling has been the dominant collection method for the data underlying the measure. This paper derives the exact distribution of |X/Y| when X and Y are independent Pearson type VII random variables. We provide an application of this result to the exchange rate data of the six major currencies. Some computer programs for use in the applications are also provided.      

Sampling Procedures for Coordinating Stratified Samples: Methods Based on Microstrata

The aim of sampling coordination is to maximize or minimize the overlap between several samples drawn successively in a population that changes over time. Therefore, the selection of a new sample will depend on the samples previously drawn. In order to obtain a larger (or smaller) overlap of the samples than the one obtained by independent selection of samples, a dependence between the samples must be introduced. This dependence will emphasize (or limit) the number of common units in the selected samples. Several methods for coordinating stratified samples, such as the Kish & Scott method, the Cotton & Hesse method, and the Rivière method, have already been developed. Using simulations, we compare the optimality of these methods and their quality of coordination. We present six new methods based on permanent random numbers (PRNs) and microstrata. These new methods have the advantage of allowing us to choose between positive or negative coordination with each of the previous samples. Simulations are run to test the validity of each of them.     

Relative Performance Evaluations in a Model of Financial Intermediation

This paper focuses on the delegation by bank managers of lending decisions to their agents, typically subordinate employees of the bank. We assume that agents may base their decisions about lending to borrowers on decisions other banks have made about these same borrowers. Then we show that there exist some lazy or negligent agents who neither directly monitor the borrower nor imitate the other banks if managers use relative performance evaluations as incentive schemes. In addition, it is shown that the learning or adjustment process of agents exhibits cyclical dynamics. Journal of Economic Literature Classification Numbers: D82, D83.     

Simulation study of the price differentiation effect in a stochastic deteriorating inventory with heterogeneous consumers – freshness sensitivity

A fixed price policy regardless of expiration date may result in unsold inventory and sales loss. Price reduction over time as the expiration date approaches motivates customers to purchase all items, including the ones that are left with only a short interval until their expiration. We conduct a discrete event simulation that captures the main characteristics of this phenomenon. Results show that a moderate differentiation of price increases profits by 6%, a larger differentiation reduces profits. Profits are the highest for freshness-oriented customers. A fixed price policy is preferred in an environment of large variance and expected near term expirations.     

Are U.S. airlines really in crisis?

This study reflects on the technical efficiency of U.S. airlines using a Bayesian random stochastic frontier model. Inferences from the Bayesian estimation indicate that the random model fits the data well and outperforms the traditional stochastic frontier model. The technical efficiency results indicate that U.S. airlines are operating at a declining efficiency rate with an average of 69.02% in 2007. Results from returns to scale are also in line with the efficiency results. More specific discussions on the current industry trends and other contributions of this study are presented and discussed.     

基于L-系统的随机树模型

由于每次由同一个确定L-系统生成的植物模型都是固定不变的,而且显得很死板。本文在考虑植物生长规律的前提下,利用随机L-系统生成了一个随机树模型,该模型形态自然、具有很强的真实感。     

What Do Farmers Want From Agri‐Environmental Scheme Design? A Choice Experiment Approach

Agri‐environmental schemes (AES) have had a limited effect on European agriculture due to farmers’ reluctance to participate. Information on how farmers react when AES characteristics are modified can be an important input to the design of such policies. This article investigates farmers’ preferences for different design options in a specific AES aimed at encouraging nitrogen fixing crops in marginal dry‐land areas in Spain. We use a choice experiment survey conducted in two regions (Aragón and Andalusia). The analysis employs an error component random parameter logit model allowing for preference heterogeneity and correlation amongst the non‐status quo alternatives. Farmers show a strong preference for maintaining their current management strategies; however, significant savings in cost or increased participation can be obtained by modifying some AES attributes.