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91.
Gabriela García‐Ayala José Luis González‐Velarde Roger Z. Ríos‐Mercado Elena Fernández 《International Transactions in Operational Research》2016,23(3):433-458
The problem of district design for the implementation of arc routing activities is addressed. The aim is to partition a road network into a given number of sectors to facilitate the organization of the operations to be implemented within the region. This problem arises in numerous applications such as postal delivery, meter readings, winter gritting, road maintenance, and municipal solid waste collection. An integer linear programming model is proposed where a novel set of node parity constraints to favor Eulerian districts is introduced. Series of instances were solved to assess the impact of these parity constraints on the objective function and deadhead distance. Networks with up to 401 nodes and 764 edges were successfully solved. The model is useful at a tactical level as it can be used to promote workload balance, compactness, deadhead distance reduction and parity in districts. 相似文献
92.
The university timetabling problem (UTP) has been studied by numerous research groups for decades. In addition to addressing hard and soft constraints, we extend the UTP by considering consecutiveness and periodicity constraints of multi-session lectures, which are common in many eastern Asian universities. Because schedulers can decide the consecutiveness and periodicity constraints for the multi-session lectures within a limited ratio, we consider these novel decision variables in our model. We develop a mixed integer linear program for the UTP. For the analysis, we convert the UTP into the three-dimensional container packing problem (3DCPP) and create a hybrid genetic algorithm (HGA), which has been shown to be efficient in solving the 3DCPP. We also develop a tabu search algorithm based on the existing UTP literature and compare the findings with that of our HGA. The results show that our HGA obtains a better solution than the tabu search algorithm in a reasonable amount of time. 相似文献
93.
In this paper we consider the problem of identifying the most influential (or central) group of nodes (of some predefined size) in a network. Such a group has the largest value of betweenness centrality or one of its variants, for example, the length-scaled or the bounded-distance betweenness centralities. We demonstrate that this problem can be modelled as a mixed integer program (MIP) that can be solved for reasonably sized network instances using off-the-shelf MIP solvers. We also discuss interesting relations between the group betweenness and the bounded-distance betweenness centrality concepts. In particular, we exploit these relations in an algorithmic scheme to identify approximate solutions for the original problem of identifying the most central group of nodes. Furthermore, we generalize our approach for identification of not only the most central groups of nodes, but also central groups of graph elements that consists of either nodes or edges exclusively, or their combination according to some pre-specified criteria. If necessary, additional cohesiveness properties can also be enforced, for example, the targeted group should form a clique or a κ-club. Finally, we conduct extensive computational experiments with different types of real-life and synthetic network instances to show the effectiveness and flexibility of the proposed framework. Even more importantly, our experiments reveal some interesting insights into the properties of influential groups of graph elements modelled using the maximum betweenness centrality concept or one of its variations. 相似文献
94.
熊明明李英郭剑毅毛存礼余正涛 《数据采集与处理》2017,32(3):636-642
通过对越南语词法特点的研究,把越南语的基本特征融入到条件随机场中(Condition random fields,CRFs),提出了一种基于CRFs和歧义模型的越南语分词方法。通过机器标注、人工校对的方式获取了25 981条越南语分词语料作为CRFs的训练语料。越南语中交叉歧义广泛分布在句子中,为了克服交叉歧义的影响,通过词典的正向和逆向匹配算法从训练语料中抽取了5 377条歧义片段,并通过最大熵模型训练得到一个歧义模型,并融入到分词模型中。把训练语料均分为10份做交叉验证实验,分词准确率达到了96.55%。与已有越南语分词工具VnTokenizer比较,实验结果表明该方法提高了越南语分词的准确率、召回率和F值。 相似文献
95.
韩煜 《计算机工程与科学》2017,39(6):1092-1096
针对多用户CDMA信号的时频域重叠特征,提出了一种新颖的时频差高精度估计方法。该方法结合扩频信号的捕获和解扩操作,以较短的信号样本和较低的计算量,仅两次时间-频率分维迭代实现了用户信号分离和时频差估计,再通过时域和频域内插进一步提高估计精度。仿真结果表明,与直接互模糊函数相关法相比,该方法能够有效提高CDMA信号时频差估计精度,降低计算量。 相似文献
96.
为了降低实时更新和存储海量地形的形变数据对动态绘制速度的影响,提出一种基于整数小波变换与限制性四叉树相结合的GPU并行动态存储与绘制算法.首先设计面向CUDA并行且无损的基于块的整数小波变换算法和SPIHT压缩算法,提高地形压缩比以减小数据传输量,同时解决了海量地形动态数据存储的编解码的实时性问题,实现了局部动态地形数据的实时存储;然后将小波系数、限制性四叉树层次结构以及模板技术相结合,提出一种自适应三角化和绘制的并行处理算法.实验结果表明,对于海量地形数据,文中算法可以在实现后端及时保存局部形变数据的同时,前端可以保持较高的绘制帧率. 相似文献
97.
98.
Duan Li Xiaoling Sun Jianjun Gao Shenshen Gu Xiaojin ZhengAuthor vitae 《Automatica》2011,47(9):2094-2098
Reachability is one of the most important behavioral properties of Petri nets. We propose in this paper a novel approach for solving the fundamental equation in the reachability analysis of acyclic Petri nets, which has been known to be NP-complete. More specifically, by adopting a revised version of the cell enumeration method for an arrangement of hyperplanes in discrete geometry, we develop an efficient solution scheme to identify firing count vector solution(s) to the fundamental equation on a bounded integer set, with a complexity bound of O((nu)n−m), where n is the number of transitions, m is the number of places and u is the upper bound of the number of firings for all individual transitions. 相似文献
99.
Any Gray code for a set of combinatorial objects defines a total order relation on this set: x is less than y if and only if y occurs after x in the Gray code list. Let ? denote the order relation induced by the classical Gray code for the product set (the natural extension of the Binary Reflected Gray Code to k-ary tuples). The restriction of ? to the set of compositions and bounded compositions gives known Gray codes for those sets. Here we show that ? restricted to the set of bounded compositions of an interval yields still a Gray code. An n-composition of an interval is an n-tuple of integers whose sum lies between two integers; and the set of bounded n-compositions of an interval simultaneously generalizes product set and compositions of an integer, and so ? put under a single roof all these Gray codes.As a byproduct we obtain Gray codes for permutations with a number of inversions lying between two integers, and with even/odd number of inversions or cycles. Such particular classes of permutations are used to solve some computational difficult problems. 相似文献
100.