一种有效的距离连接选择度估计方法

距离连接在空间数据库中有着广泛的应用,而距离连接的选择度估计是优化距离查询的基础。通过综合分析和比较了现有的选择度估计技术,提出了一种利用米诃夫斯基和与直方图进行距离连接选择度估计的新方法。实验结果证明该种方法能够有效地进行距离连接选择度估计。     

数学解题教学中寻求隐含条件的规律探索

中学数学教学中,解数学难题的过程就是从题设中不断地挖掘并利用隐含条件进行推理和变形的过程。数学题中的隐含条件形形色色,花样繁多,但从对解题过程的影响看,又可以分为制约解题方向的隐含条件、制约解题思路的隐含条件、制约解题准确性的隐含条件等三类隐含条件。只要我们把握了难题中隐含条件的规律特征,运用我们获得的数学知识,结合适当的数学思想和数学方法,就可以轻松解决难题了。     

UCAV空面多目标攻击三维轨迹规划技术

研究了单架无人作战飞机(UCAV)攻击多个地面目标的三维轨迹规划问题。首先,将问题形式化为一类特殊的旅行商问题(TSP),即带动力学约束的邻域访问TSP问题(DCTSPN)。其次,针对规划空间维度过高、搜索代价过大的问题,提出了一种基于概率路标图(PRM)的方法。该方法借鉴了基于采样的运动规划方法的思想,并结合多种组合优化技术,将原本连续状态空间中的轨迹规划问题转化为离散拓扑图上的路由问题。求解过程分为离线预处理和在线查询两个阶段。离线阶段采用Halton拟随机采样算法及Noon-Bean转换方法,将原问题转化为经典的非对称旅行商问题(ATSP);在线阶段根据战场态势的实时变化,快速更新路标图,然后采用LKH算法在线求解问题的近似最优解。为了保证生成的飞行轨迹满足平台的运动学/动力学约束,算法基于Gauss伪谱法构建了局部轨迹规划器。最后,以攻击时间最短为优化指标对算法进行了仿真实验。结果表明,本文提出的方法能够以较高的精度和在线收敛速度生成真实可行的、较优的多目标攻击轨迹。     

基于区间数的第4代战斗机空战效能评估

根据第4代战斗机所具有的典型特征,建立了第4代战斗机的空战效能评估指标体系。采用区间数特征向量法确定了效能评估指标体系中的各指标的权重,给出了定量指标和定性指标的规范化方法,提出了采用区间数形式的加权和关系进行效能指标聚合的方法。最后,通过实例验证了所建立的空战效能评估指标体系的合理,评估方法的有效、可行。     

Multiple subset sum with inclusive assignment set restrictions

In a traditional multiple subset sum problem (MSSP), there is a given set of items and a given set of bins (or knapsacks) with identical capacities. The objective is to select a subset of the items and pack them into the bins such that the total weight of the selected items is maximized. However, in many applications of the MSSP, the bins have assignment restrictions. In this article, we study the subset sum problem with inclusive assignment set restrictions, in which the assignment set of one item (i.e., the set of bins that the item may be assigned to) must be either a subset or a superset of the assignment set of another item. We develop an efficient 0.6492‐approximation algorithm and test its effectiveness via computational experiments. We also develop a polynomial time approximation scheme for this problem. © 2011 Wiley Periodicals, Inc. Naval Research Logistics, 2011     

Optimal control of a capacitated inventory system with multiple demand classes

This article studies the optimal control of a periodic‐review make‐to‐stock system with limited production capacity and multiple demand classes. In this system, a single product is produced to fulfill several classes of demands. The manager has to make the production and inventory allocation decisions. His objective is to minimize the expected total discounted cost. The production decision is made at the beginning of each period and determines the amount of products to be produced. The inventory allocation decision is made after receiving the random demands and determines the amount of demands to be satisfied. A modified base stock policy is shown to be optimal for production, and a multi‐level rationing policy is shown to be optimal for inventory allocation. Then a heuristic algorithm is proposed to approximate the optimal policy. The numerical studies show that the heuristic algorithm is very effective. © 2011 Wiley Periodicals, Inc. Naval Research Logistics 58: 43–58, 2011     

边界元角点问题的重节点法分析

应用重节点法处理三维弹性力学角节点问题,采用等参变换插值逼近的方法离散边界积分方程,解决了由于角节点表面力不连续带来的方程求解困难问题。算例分析结果表明,该方法具有操作简单,计算方便,求解结果满足计算精度的要求等优点,尤其在角点存在应力集中场合更具优越性。     

当前高校教学评估中的问题及对策研究

高校教学评估是高等教育质量保障体系的重要方面,对当前我国高校教学评估中普遍存在的问题应引起足够重视并提出相应的对策。     

一类带配送中心运输问题的容量扩张模型研究

运输问题一般采用表上作业法来解决,考虑一类带配送中心的运输问题,若仍采用表上作业法,会使问题复杂化.文中采用一种构造辅助网络的方法:在运输网络中将每个配送中心均拆分成两个点,连接两点形成新弧,构造出新的网络,并给每条弧赋予参数,将此类运输问题转换为最小费用流模型来解决,可以使问题模型和运算简单化.在此基础上,考虑运输网络中配送中心和边的容量扩张问题.     

An inspection game: Taking account of fulfillment probabilities of players' aims

This paper deals with an inspection game of customs and a smuggler. The customs can take two options of assigning a patrol or not. The smuggler has two strategies of shipping its cargo of contraband or not. Two players have several opportunities to take actions during a limited number of days. When both players do, there are some possibilities that the customs captures the smuggler and, simultaneously, the smuggler possibly makes a success of the smuggling. If the smuggler is captured or there remain no days for playing the game, the game ends. In this paper, we formulate the problem into a multi‐stage two‐person zero‐sum stochastic game and investigate some characteristics of the equilibrium solution, some of which are given in a closed form in a special case. There have been some studies so far on the inspection game. However, some consider the case that the smuggler has only one opportunity of smuggling or the perfect‐capture case that the customs can certainly arrest the smuggler on patrol, and others think of a recursive game without the probabilities of fulfilling the players' purposes. In this paper, we consider the inspection game taking account of the fulfillment probabilities of the players' aims. © 2006 Wiley Periodicals, Inc. Naval Research Logistics, 2006