Simple paths with exact and forbidden lengths

We study new decision and optimization problems of finding a simple path between two given vertices in an arc weighted directed multigraph such that the path length is equal to a given number or it does not fall into the given forbidden intervals (gaps). A fairly complete computational complexity classification is provided and exact and approximation algorithms are suggested.     

连续求解样本协方差矩阵迹的快速递推算法

为解决当样本数据不断增加时,利用传统方法反复计算样本协方差迹耗时多的缺点,提出了一种快速递推算法。理论分析和仿真试验都表明,算法的时间复杂度比传统的方法降低了一个数量级,从而大大减少了计算时间。     

On efficient algorithms for finding efficient salvo policies

We consider the salvo policy problem, in which there are k moments, called salvos, at which we can fire multiple missiles simultaneously at an incoming object. Each salvo is characterized by a probability p_i: the hit probability of a single missile. After each salvo, we can assess whether the incoming object is still active. If it is, we fire the missiles assigned to the next salvo. In the salvo policy problem, the goal is to assign at most n missiles to salvos in order to minimize the expected number of missiles used. We consider three problem versions. In Gould's version, we have to assign all n missiles to salvos. In the Big Bomb version, a cost of B is incurred when all salvo's are unsuccessful. Finally, we consider the Quota version in which the kill probability should exceed some quota Q. We discuss the computational complexity and the approximability of these problem versions. In particular, we show that Gould's version and the Big Bomb version admit pseudopolynomial time exact algorithms and fully polynomial time approximation schemes. We also present an iterative approximation algorithm for the Quota version, and show that a related problem is NP-complete.     

Scheduling for parallel dedicated machines with a single server

This paper examines scheduling problems in which the setup phase of each operation needs to be attended by a single server, common for all jobs and different from the processing machines. The objective in each situation is to minimize the makespan. For the processing system consisting of two parallel dedicated machines we prove that the problem of finding an optimal schedule is N P‐hard in the strong sense even if all setup times are equal or if all processing times are equal. For the case of m parallel dedicated machines, a simple greedy algorithm is shown to create a schedule with the makespan that is at most twice the optimum value. For the two machine case, an improved heuristic guarantees a tight worst‐case ratio of 3/2. We also describe several polynomially solvable cases of the later problem. The two‐machine flow shop and the open shop problems with a single server are also shown to be N P‐hard in the strong sense. However, we reduce the two‐machine flow shop no‐wait problem with a single server to the Gilmore—Gomory traveling salesman problem and solve it in polynomial time. © 2000 John Wiley & Sons, Inc. Naval Research Logistics 47: 304–328, 2000     

Scheduling to minimize the total compression and late costs

We consider a single-machine scheduling model in which the job processing times are controllable variables with linear costs. The objective is to minimize the sum of the cost incurred in compressing job processing times and the cost associated with the number of late jobs. The problem is shown to be NP-hard even when the due dates of all jobs are identical. We present a dynamic programming solution algorithm and a fully polynomial approximation scheme for the problem. Several efficient heuristics are proposed for solving the problem. Computational experiments demonstrate that the heuristics are capable of producing near-optimal solutions quickly. © 1998 John Wiley & Sons, Inc. Naval Research Logistics 45: 67–82, 1998     

Scheduling a production–distribution system to optimize the tradeoff between delivery tardiness and distribution cost

We consider a make‐to‐order production–distribution system with one supplier and one or more customers. A set of orders with due dates needs to be processed by the supplier and delivered to the customers upon completion. The supplier can process one order at a time without preemption. Each customer is at a distinct location and only orders from the same customer can be batched together for delivery. Each delivery shipment has a capacity limit and incurs a distribution cost. The problem is to find a joint schedule of order processing at the supplier and order delivery from the supplier to the customers that optimizes an objective function involving the maximum delivery tardiness and the total distribution cost. We first study the solvability of various cases of the problem by either providing an efficient algorithm or proving the intractability of the problem. We then develop a fast heuristic for the general problem. We show that the heuristic is asymptotically optimal as the number of orders goes to infinity. We also evaluate the performance of the heuristic computationally by using lower bounds obtained by a column generation approach. Our results indicate that the heuristic is capable of generating near optimal solutions quickly. Finally, we study the value of production–distribution integration by comparing our integrated approach with two sequential approaches where scheduling decisions for order processing are made first, followed by order delivery decisions, with no or only partial integration of the two decisions. We show that in many cases, the integrated approach performs significantly better than the sequential approaches. © 2005 Wiley Periodicals, Inc. Naval Research Logistics, 2005     

舰艇协同作战导弹防御模型研究

舰艇协同作战是未来战争的主要作战形式,导弹防御是其主要的作战职责.运用信息论的方法对舰艇协同作战中敌方导弹发射策略的不确定性进行建模,运用可靠性理论对协作效果进行建模,并引进知识的概念作为其度量,同时用边的函数对网络复杂性进行建模,综合这两种因素在以最大化防御时间为总的决策目标,以己方导弹储备和敌方来袭速率为决策因素对导弹防御作出辅助决策.     

GENDER AWARENESS IN RESEARCH AND POLICY MAKING

Abstract

There is an assumption that we can enhance peacebuilding by improving the tools that we use for assessments, planning and evaluation. However, the focus on tools creates the impression that peacebuilding challenges are technical. Improving tools is not meaningless, but our preoccupation with tools has a negative effect when it becomes a front for avoiding dealing with the deeper inherent contradictions in peacebuilding. There are limits to our knowledge and our ability to engineer specific outcomes in complex systems. There are unrealistically high expectations of coherence, unity of purpose and cooperation among peacebuilding actors. Peacebuilding agents are interconnected, but that does not imply that they have the same objectives, mandates, principles and values. Interconnected problems call for interconnected responses, not for one coherent response. Coherence should not be about negotiating a common position, and then promoting it regardless of changing dynamics. Coherence should be about continuously managing competing interests and interdependencies. The interaction between dissention, competition for resources, and the tension between different approaches and policy choices is not only normal but necessary to ensure the optimal functioning of the system.     

Zodiac算法新的不可能差分攻击

重新评估了Zodiac算法抵抗不可能差分攻击的能力。通过分析Zodiac算法的线性层,给出了Zodiac算法两条新的14轮不可能差分。利用新的不可能差分,结合Early-Abort技术对完整16轮的Zodiac算法进行了不可能差分攻击。攻击过程中一共恢复6个字节的密钥,其时间复杂度只有2_32.6次加密,数据复杂度约为2_85.6个明文,该攻击结果与已有最好的结果相比,时间复杂度降低了一个因子2₃₃。结果表明由于Zodiac算法线性层的扩散性差,使得该算法对不可能差分分析是不免疫的。     

Zodiac算法新的不可能差分攻击

#重新评估了Zodiac算法抵抗不可能差分攻击的能力。通过分析Zodiac算法的线性层,给出了Zodiac算法两条新的14轮不可能差分。利用新的不可能差分,结合Early-Abort技术对完整16轮的Zodiac算法进行了不可能差分攻击。攻击过程中一共恢复6个字节的密钥,其时间复杂度只有2_32.6次加密,数据复杂度约为2_85.6个明文,该攻击结果与已有最好的结果相比,时间复杂度降低了一个因子2₃₃。结果表明由于Zodiac算法线性层的扩散性差,使得该算法对不可能差分分析是不免疫的。