离散点集最小包围圆算法分析与改进

针对平面上的离散点集求取最小包围圆的问题,评述现有算法并给出一种 改进算法,称为较远点对定义初始包围圆的增量算法。首先概述了几条对算法理解和设计有 直接影响的最小包围圆性质或判定;然后对求取最小包围圆的随机增量算法、最远点优先渐 近算法、对偶决策算法等3 种典型算法进行概述和简要分析;再对随机增量算法和最远点优 先渐近算法进行改进;最后,以二维区域随机点集、一维共线随机点集和共线有序点集3 类数据进行实验对比。实验结果表明,最远点优先渐近算法是过去3 种算法中效率最高的; 论文提出的较远点对定义初始包围圆的增量算法大大提高了随机增量算法的时间效率,是该 文所列举的方法中最快的算法,并且是一种确定性算法。离散点集最小包围圆的快速计算有 助于碰撞检测和机器人等领域的广泛应用。     

On the smallest enclosing information disk

We present a generalization of Welzl's smallest enclosing disk algorithm [E. Welzl, Smallest enclosing disks (balls and ellipsoids), in: New Results and New Trends in Computer Science, in: Lecture Notes in Computer Science, vol. 555, Springer, 1991, pp. 359-370] for point sets lying in information-geometric spaces. Given a set of points equipped with a Bregman divergence as a (dis)similarity measure, we investigate the problem of finding its unique (circum)center defined as the point minimizing the maximum divergence to the point set. As an application, we show how to solve a statistical model estimation problem by computing the center of a finite set of univariate normal distributions.     

Improved pruning of large data sets for the minimum enclosing ball problem

Minimum enclosing ball algorithms are studied extensively as a tool in approximation and classification of multidimensional data. We present pruning techniques that can accelerate several existing algorithms by continuously removing interior points from the input. By recognizing a key property shared by these algorithms, we derive tighter bounds than have previously been presented, resulting in twice the effect on performance. Furthermore, only minor modifications are required to incorporate the pruning procedure. The presented bounds are independent of the dimension, and empirical evidence shows that the pruning procedure remains effective in dimensions up to at least 200. In some cases, performance improvements of two orders of magnitude are observed for large data sets.     

针对大样本集的融合模糊系统

为了解决处理大样本和超大样本数据集消耗大量时间和准确性问题,本文将中心约束型最小包含球(CCMEB)理论融合对TSK模糊系统(Takagi-Sugeno-Kang Fuzzy System)重新审视和改进而成的双层TSK模糊系统CTSK（Centralized TSK Fuzzy System）模糊系统。两种系统取长补短结合成新的适合处理大样本数据的算法系统。仿真实验研究分析了不同的模糊规则对新算法的影响以及所提出的算法与另外三种国际上较为先进的处理大数据算法的性能比较。结果表明所提出的算法对处理大样本数据的有效性和快速性。     

On the All-Farthest-Segments problem for a planar set of points

In this note, we outline a very simple algorithm for the following problem: Given a set S of n points p₁,p₂,p₃,…,pn in the plane, we have O(n²) segments implicitly defined on pairs of these n points. For each point pi, find a segment from this set of implicitly defined segments that is farthest from pi. The time complexity of our algorithm is in O(nh+nlogn), where n is the number of input points, and h is the number of vertices on the convex hull of S.     

On the design optimization of built-up stiffened steel beams with buckling and frequency constraints

The literature on the structural design optimization of steel-plate girders indicates a need for more refined research studies to obtain optimal designs by formulating and solving the design problem that combines structural sizing and shape parameters in one unified, constrained problem. For this purpose, the structural optimization design problem of stiffened steel-plate girders is formulated with specified loading conditions and constraints on strength and serviceability considerations including limits on fundamental frequency and buckling modes. The finite-element method-based model is used to define the objective function and the structural/geometric response functions, while the geometric domain elements are used to systematically perturb the structural shape during the search for an optimal shape of the structure. The mathematical statement of the gradient-based-design problem is solved for an optimal structural size and shape with buckling and frequency constraints in addition to the traditional strength constraints. The numerical results obtained are compared with results obtained from a less formal ad hoc design procedure, and some conclusions are drawn to emphasize the design benefits obtained from solving the design problem for optimal structural size and shape.     

Shortest paths of bounded curvature in the plane

Given two oriented points in the plane, we determine and compute the shortest paths of bounded curvature joining them. This problem has been solved recently by Dubins in the no-cusp case, and by Reeds and Shepp otherwise. We propose a new solution based on the minimum principle of Pontryagin. Our approach simplifies the proofs and makes clear the global or local nature of the results.     

An approximate solution of the problem of optimal control over elliptic systems in domains of arbitrary form

A combination of the net method and method of fictitious domains is used for solving the problem of optimal control over elliptic systems in domains of arbitrary form. As is shown, the proposed difference scheme has the order of accuracy O(h^1/2) in the net norm W^1/2 (ω). Translated from Kibernetika i Sistemnyi Analiz, No. 6, pp. 3–8, November–December, 1999.     

On a method of Porter in the eigenvalue assignment problem†

In a recent article in this Journal, Porter (1969 a) described a simple and attractive alternative procedure for synthesizing a linear feedback control law which will realize a certain pre-selected closed-loop eigenvalue pattern for a linear dynamical system. The purpose of the present note is to investigate the conditions for applicability of Porter's method. In addition, another method is proposed.     

On the approximation problem of common fixed points for a finite family of non-self asymptotically quasi-nonexpansive-type mappings in Banach spaces

The purpose of this paper is to introduce the concept of non-self asymptotically quasi-nonexpansive-type mappings and to construct a iterative sequence to converge to a common fixed point for a finite family of non-self asymptotically quasi-nonexpansive-type mappings in Banach spaces. The results presented in this paper improve and extend the corresponding results in Alber, Chidume and Zegeye [Ya.I. Alber, C.E. Chidume, H. Zegeye, Approximating of total asymptotically nonexpansive mappings, Fixed Point Theory and Applications (2006) 1–20. Article ID10673], Ghosh and Debnath [M.K. Ghosh, L. Debnath, Convergence of Ishikawa iterates of quasi-nonexpansive mappings, Journal of Mathematical Analysis and Applications 207 (1997) 96–103], Liu [Q.H. Liu, Iterative sequences for asymptotically quasi-nonexpansive type mappings, Journal of Mathematical Analysis and Applications 259 (2001) 1–37; Q.H. Liu, Iterative sequences for asymptotically quasi-nonexpansive mappings with error member, Journal of Mathematical Analysis and Applications 259 (2001) 18–24; Q.H. Liu, Iteration sequences for asymptotically quasi-nonexpansive mapping with an error member of uniform convex Banach space, Journal of Mathematical Analysis and Applications 266 (2002) 468–471], Petryshyn [W.V. Petryshyn, T.E. Williamson Jr., Strong and weak convergence of the sequence of successive approximations for quasi-nonexpansive mappings, Journal of Mathematical Analysis and Applications 43 (1973) 459–497], Quan and Chang [J. Quan, S.S. Chang, X.J. Long, Approximation common fixed point of asymptotically quasi-nonexpansive type mappings by the finite steps iterative sequences, Fixed Point Theory and Applications V (2006) 1–38. Article ID 70830], Shahzad and Udomene [N. Shahzad, A. Udomene, Approximating common fixed point of two asymptotically quasi-nonexpansive mappings in Banach spaces, Fixed Point Theory and Applications (2006) 1–10. Article ID 18909] Xu [B.L. Xu, M.A. Noor, Fixed-point iterations for asymptotically nonexpansive mappings in Banach spaces, Journal of Mathematical Analysis and Applications 267 (2002) 444–453], Zhang [S.S. Zhang, Iterative approximation problem of fixed points for asymptotically nonexpansive mappings in Banach spaces, Acta Mathematicae Applicatae Sinica 24 (2001) 236–241] and Zhou and Chang [Y.Y. Zhou, S.S. Chang, Convergence of implicit iteration process for a finite family of asymptotically nonexpansive mappings in Banach spaces, Numerical Functional Analysis and Optimization 23 (2002) 911–921].     

On Stubborn Sets in the Verification of Linear Time Temporal Properties

The stubborn set method is one of the methods that try to relieve the state space explosion problem that occurs in state space generation. This article is concentrated on the verification of next-time-less LTL (linear time temporal logic) formulas with the aid of the stubborn set method. The essential contribution is a theorem that gives us a way to utilize the structure of the checked formula when the stubborn set method is used and there is no fairness assumption. The theorem also applies to verification under fairness assumptions, including those which allow a predefined subset of actions to be treated unfairly.This work has been funded by the National Technology Agency of Finland, the Academy of Finland, Helsinki Graduate School in Computer Science and Engineering, Nokia Research Center, Nokia Networks, Elisa Communications, and Finnish Rail Administration.     

On the value of predictive information in a scheduling problem

It is well known that given a set of jobs to be scheduled on a single server, the Shortest Time First (STF) policy will minimize mean wait. Unfortunately, service times are often unknown, so STF cannot be used. However, approximate service times might be known, in terms of predicted values obtained from other characteristics of the jobs, and thus one might therefore consider scheduling according to these. In this paper, the feasibility of such an approach is investigated, and factors affecting its efficiency are identified. A comparison of this approach to that of Round Robin scheduling is also made.     

On the difference in control performance of interval type-2 fuzzy PI control system with different FOU shapes

Interval type-2 fuzzy logic controllers (IT2-FLCs) have been attracting a lot of attention. However, challenges in designing IT2-FLCs still remain. One of the main challenges is to choose the appropriate FOU shape for interval type-2 fuzzy sets (IT2-FSs). This paper aims to analyse the differences in control performance between three IT2 fuzzy PI controllers (IT2-F-PICs) with different FOU shapes as antecedent sets, namely the triangular top wide IT2 fuzzy set, the triangular bottom wide IT2 fuzzy set and the trapezoidal (also called parallel) IT2 fuzzy set. First, the analytical structures of these IT2-FLCs are derived and the mathematical input–output equations are obtained. Three interesting differences between the analytical structures and input–output relationship of the IT2-F-PICs are then presented. From the differences in the analytical structures of the three IT2-F-PICs and numerical simulation results, it is demonstrated that IT2-F-PICs with trapezoidal (IT2-F-PI-P) and triangular bottom wide (IT2-F-PI-BW) antecedent sets with the potential to provide faster transient response and faster settling time than the IT2-F-PICs with triangular top wide (IT2-F-PI-TW). In addition, IT2-F-PI-P is better able to handle plant uncertainties and disturbances than IT2-F-PI-BW and IT2-F-PI-TW. The contribution of this paper is to provide insights into the performance differences between different FOU shaped controllers, which in turns allowing control designers to select the appropriate FOU shape in order to meet design requirements.     

试析如何在三网融合背景下搞好有线电视的发展

三网融合在给有线电视带来了机遇的同时,也带来了一定的挑战。这就需要相关工作人员抓住契机,努力做好有线电视的发展工作。通过分析三网融合背景下有线电视面临的机遇和挑战,提出了有效发展有线电视的可行性措施。     

高职程序设计课程的教学探讨

在高职院校中,程序设计课程不仅是计算机专业的主干课程,在非计算机专业的教学中也逐步占据了主导地位。针对此类课程枯燥、难懂等问题,该文从课程教学、课程设计和考试考核三个方面着手,探讨在教学中如何培养学生主动学习的兴趣,使学生通过本课程的学习,掌握程序设计的方法,具备小型项目开发的能力。     

浅谈高中设计基础教育

面对艺术高考扩招的新形势,为提高升学率,一些普通高中学校在不考虑教学条件和专业教师等综合条件的情况下,盲目开设工艺美术或艺术设计专业。但教学环境、师资问题、图书问题、社会需求等诸类条件并不具备。要想使高中阶段设计基础教育专业趋向规范化发展就必须先从根本上解决旧的教学模式、师资的培养以及专业的布局等诸多问题。     

On the Existence and Uniqueness of Equilibrium Situations in Markovian Games with Discounting

Markovian (stochastic) two-person games with discounting are considered. It is proved that if the set of states of such a game and the set of decisions of the players are finite, then the game has values and both players have optimal stationary strategies. The proof, which is based on the principle of contracting mappings, is constructive and leads to a recurrent algorithm of finding solutions of the game. The question of uniqueness of an equilibrium situation in the game considered is also discussed. In addition to the Markovian game with discounting in the context of the principle of contracting mappings, its subgame, namely, a Markovian decision process with discounting is also studied.     

On the absence of strict boundaries—Vagueness, haziness, and fuzziness in philosophy, science, and medicine

This contribution deals with developments in the history of philosophy, logic, and mathematics during the time before and up to the beginning of fuzzy logic. Even though the term “fuzzy” was introduced by Lotfi A. Zadeh in 1964/1965, it should be noted that older concepts of “vagueness” and “haziness” had previously been discussed in philosophy, logic, mathematics, applied sciences, and medicine. This paper delineates some specific paths through the history of the use of these “loose concepts”. Vagueness was avidly discussed in the fields of logic and philosophy during the first decades of the 20th century—particularly in Vienna, at Cambridge and in Warsaw and Lvov. An interesting sequel to these developments can be seen in the work of the Polish physician and medical philosopher Ludwik Fleck.Haziness and fuzziness were concepts of interest in mathematics and engineering during the second half of the 1900s. The logico-philosophical history presented here covers the work of Bertrand Russell, Max Black, and others. The mathematical–technical history deals with the theories founded by Karl Menger and Lotfi Zadeh. Menger's concepts of probabilistic metrics, hazy sets (ensembles flous) and micro-geometry as well as Zadeh's theory of fuzzy sets paved the way for the establishment of soft computing methods using vague concepts that connote the nonexistence of sharp boundaries.     

浅议现代平面设计中对中国画意境的借鉴与运用

文章从中国画意境角度入手,对中国画深厚哲学思想,灵活多样的空间布局,随类赋彩的笔墨情趣,曲直多变的线条语言在现代平面设计中的灵活运用进行简述,挖掘适合现代人审美情趣,又对设计语言具有非凡意义的中国式平面设计元素,以此赋予现代平面设计以深厚的文化底蕴和丰富的内涵。     

Analyzing the problem of unsustainable health information systems in less-developed economies: Case studies from Tanzania and Mozambique

Most of donor-supported information technology (IT)–based projects developed or implemented in less-developed economies (LDEs) end up as complete or partial failures or unsustainable. Notably, a number of intra-organizational and external factors are associated with this problem, including inadequate infrastructure and human resource capacity, fragmented donor policy, and lack of policies to manage the sustainability problem. Accordingly, IT initiatives are often donor-driven, top-down, and hijacked by top managers who (normally) do not have adequate skills, but have enormous power to enforce such initiatives across organizational hierarchies.

In analyzing the concepts from sustainability and institutionalization, key insights towards a better understanding of the problem of unsustainability are developed. It is argued that health information systems (HISs) become sustainable if they are institutionalized in the sense of being integrated into the everyday routine of the user organization. However, a sustainable HIS should also be flexible enough to allow changes as the user needs change. Moreover, introduction of a new HIS is not only a technical change, but requires the cultivation and institutionalization of a new kind of culture.

Through a comparative case analysis of the HIS development and implementation processes in Tanzania and Mozambique, we have identified two sets of relationships, between the Ministry of Health (MoH) and donor agencies and between the MoH and software development agencies as critical and contributing factors to the unsustainability of a HIS. Given this setting, we highlight three key strategies for dealing with the problem of unsustainability in LDEs: (a) integration of a HIS, (b) local shaping of new cultures, and (c) cultivation approach to systems development. © 2005 Wiley Periodicals, Inc.