Revisiting the cluster-based paradigm for implicit search result diversification     

Hai-Tao Yu  Adam Jatowt  Roi Blanco  Hideo Joho  Joemon M. Jose  Long Chen  Fajie Yuan 《Information processing & management》2018,54(4):507-528

To cope with ambiguous and/or underspecified queries, search result diversification (SRD) is a key technique that has attracted a lot of attention. This paper focuses on implicit SRD, where the subtopics underlying a query are unknown. Many existing methods appeal to the greedy strategy for generating diversified results. A common practice is using a heuristic criterion for making the locally optimal choice at each round. As a result, it is difficult to know whether the failures are caused by the optimization criterion or the setting of parameters. Different from previous studies, we formulate implicit SRD as a process of selecting and ranking k exemplar documents through integer linear programming (ILP). The key idea is that: for a specific query, we expect to maximize the overall relevance of the k exemplar documents. Meanwhile, we wish to maximize the representativeness of the selected exemplar documents with respect to the non-selected documents. Intuitively, if the selected exemplar documents concisely represent the entire set of documents, the novelty and diversity will naturally arise. Moreover, we propose two approaches ILP4ID (Integer Linear Programming for Implicit SRD) and AP4ID (Affinity Propagation for Implicit SRD) for solving the proposed formulation of implicit SRD. In particular, ILP4ID appeals to the strategy of bound-and-branch and is able to obtain the optimal solution. AP4ID being an approximate method transforms the target problem as a maximum-a-posteriori inference problem, and the message passing algorithm is adopted to find the solution. Furthermore, we investigate the differences and connections between the proposed models and prior models by casting them as different variants of the cluster-based paradigm for implicit SRD. To validate the effectiveness and efficiency of the proposed approaches, we conduct a series of experiments on four benchmark TREC diversity collections. The experimental results demonstrate that: (1) The proposed methods, especially ILP4ID, can achieve substantially improved performance over the state-of-the-art unsupervised methods for implicit SRD. (2) The initial runs, the number of input documents, query types, the ways of computing document similarity, the pre-defined cluster number and the optimization algorithm significantly affect the performance of diversification models. Careful examinations of these factors are highly recommended in the development of implicit SRD methods. Based on the in-depth study of different types of methods for implicit SRD, we provide additional insight into the cluster-based paradigm for implicit SRD. In particular, how the methods relying on greedy strategies impact the performance of implicit SRD, and how a particular diversification model should be fine-tuned.  相似文献   

线状需求下两阶段设施选址问题     

王紫萌  周建勤 《上海海事大学学报》2020,41(3):60-65

鉴于大型交通线路建设项目的物资需求随时间变化(在初期阶段需求较低;在后续阶段项目全面展开,需求显著上升),本文采用线积分对沿线连续分布的线状物资需求进行刻画,构建两阶段设施选址模型,第一阶段进行部分设施的选址,第二阶段对剩余设施选址,以实现系统总成本最低的目标。针对模型特点,设计基于Voronoi图的两阶段交替定位-分配(alternative location-allocation,ALA)算法进行求解,并进行实例分析,比较两阶段模型与传统模型的异同。研究表明,将两阶段设施选址模型应用于交通线路建设项目多物流节点选址,能节约运营成本,并缓解初期资金压力。  相似文献   

Digital Module 16: Longitudinal Data Analysis     

Jeffrey R. Harring  Tessa L. Johnson 《Educational Measurement》2020,39(3):137-138

In this digital ITEMS module, Dr. Jeffrey Harring and Ms. Tessa Johnson introduce the linear mixed effects (LME) model as a flexible general framework for simultaneously modeling continuous repeated measures data with a scientifically defensible function that adequately summarizes both individual change as well as the average response. The module begins with a nontechnical overview of longitudinal data analyses drawing distinctions with cross-sectional analyses in terms of research questions to be addressed. Nuances of longitudinal designs, timing of measurements, and the real possibility of missing data are then discussed. The three interconnected components of the LME model—(1) a model for individual and mean response profiles, (2) a model to characterize the covariation among the time-specific residuals, and (3) a set of models that summarize the extent that individual coefficients vary—are discussed in the context of the set of activities comprising an analysis. Finally, they demonstrate how to estimate the linear mixed effects model within an open-source environment (R). The digital module contains sample R code, diagnostic quiz questions, hands-on activities in R, curated resources, and a glossary.  相似文献   

Role of teacher-related factors and educational resources in science literacy: An international perspective     

《Studies in Educational Evaluation》2020

The study evaluated the relationship among teaching, leadership, teacher certification, student and teacher number related factors, and index of economic, social and cultural status (ESCS), and science literacy from an international comparative perspective. 2015 dataset of the Programme for International Student Assessment for Turkey, Singapore, the United States, Korea, Italy, and Brazil was used. Two-level hierarchical linear models were established for analysis. Results revealed that school ESCS was the best predictor of science literacy across six countries and additionally teacher-related factors came to the forefront of science literacy performance. The study underlined policymakers should focus primarily on policies that increase equity in education. Furthermore, the effectiveness of investments made in factors related to leadership, teacher certification, the number of students and teachers, which contribute very little to science literacy performance, need to be more questioned. Inferences about the findings were discussed in detail, and recommendations for further research were made.  相似文献   

2~n-周期序列的k错线性复杂度期望的界     

唐淼 《巢湖学院学报》2011,13(3):1-4

对于有限域F2上的满线性复杂度的2n-周期序列和奇数k≥3,通过对k错线性复杂度的取值范围和相应的序列个数的分析,得到其k错线性复杂度期望的上界和下界。  相似文献   

在线性规划教学中培养学生数学建模能力初探     

韦程东  林绍松  韦莹莹 《高教论坛》2008,(5)

本文主要阐述如何在线性规划教学中培养学生数学建模能力,让学生了解如何运用所学的线性规划知识去分析和解决实际问题,提高学生的应用能力和创新能力.  相似文献   

线性空间中基的扩充方法     

郭刘龙 《雁北师范学院学报》2006,22(2):69-70

给出了n维线性空间中线性无关向量组扩充为基的一般方法．  相似文献   

Adaptive Observer-Based Fault Estimate for Nonlinear Systems     

宗群  刘文静刘利 《天津大学学报(英文版)》2006,12(6):425-428

In recent years, fault detection and isolation(FDI) technologies have been developing rapidly.Among them the observer-based fault detection andisolation technology for nonlinear systems are the mostattractive research areas, and lots of promising resultscan be found in survey papers[1]. Generally, thereare several kinds of strategies for observer-based FDIin nonlinearsystems such as unknown inputs observer-based FDI[2], and adaptive observer-based FDI[3]. Insome cases, fault accommodation…  相似文献   

线性方程组相容性定理的新证法     

刘锋 《天津职业院校联合学报》2002,4(1):87-91

线性方程组解的判定在线性代数教学中具有十分重要的作用，但线性方程组相容性定理的传统证明方法需要较多的理论准备，现研究以克莱姆法则和行列式为工具，仅借用矩阵的秩这一概念，给出线性方程组相容性定理一种新的证明方法。  相似文献   

Analysis of Second-Order Effect in Frame     

毕继红  丛蓉  张利华 《天津大学学报(英文版)》2004,10(1):16-18

The second-order effect is the interaction between the vertical load and the deformation in a vertically forced element. In order to deduce a more brief but practical method, which has considered the second-order effect in a sway frame, some factors which affect the second-order deformation in a sway frame should be generalized based on a more accurate method. Nonlinear finite element is adopted in this paper, and according to this theory, a program, which can calculate the inner force and the deformation of the sway frame considering the second-order effects is coded.  相似文献