用图的着色方法求解考试时间安排问题

无向图的m着色问题已被证明为NP-难度问题,若已知图由带权值的团所构成,可用m种颜色对该图进行着色.给出了一种能在多项式时间内进行的新算法,可得到一个可接受的方案.此算法改善了求解的时间复杂度,通过一个考试时间安排的实例说明了本算法的可行性、实用性和优越性.     

SizeScale:求解旅行商问题(TSP)的新算法

旅行商（TSP）问题是组合优化中最典型的NP－Hard问题之一，目前关于该问题的启发式算法主要分布为两类：环路构造算法和环路改进算法，对于第1类算法，首次提出了在环路构造中成批加入顶点，同时在构造过程对环路进行局部优化的思想，由上得到了一种新的算法：SizeScale-Construct，它的解质量极大地改进了现有的环路构造算法，对于2类算法，在分析局部最优解与全局最优解之间关系的基础上，提出了另一个采用局部最优解的交集作为初始环路的新算法：SizeScale-Improve，实验结果表明该算法在解的质量和求解速度上都较大地改进了现有最好的环路改进算法；另一方面，理论上对于最坏情况和平均情况时间复杂度的分析表明这两个算法是实用的。     

图着色问题的混合遗传算法

针对图着色对顶点划分的本质特征,提出了基于度的种群初始化方法和交集杂交算子;为加快算法的收敛速度,设计了新的贪婪局部搜索算子来改进杂交产生的后代个体。在此基础上,提出了图着色问题的一种新的混合遗传算法,对10个标准算例的仿真结果表明,新混合遗传算法可以获得问题高质量的解,是一种有潜力的算法。     

表调度算法的并行化研究

当目标处理器个数大于2时，调度任意结构并行任务图并获取最优解的问题是NP完全难题。表调度算法作为一类代表性的启发式任务调度算法具有调度性能较好而时间复杂度较低的优点。但当任务图的规模较大时表调度算法的耗时也很可观，无疑并行表调度算法是一种好的解决方法。本文在串行算法LBP的基础上提出了一个新的表调度并行算法PLBP，该算法在保证与串行算法同样调度性能的前提下，时间复杂度有较大的改善。同时，与已有的表调度并行算法相比较，PLBP算法有更小的时间复杂度。     

社交网络中正影响支配集问题的轮转贪心算法

社交网络中最小正影响支配集问题是一个NP难度的组合优化问题,针对该问题,目前有2种典型的贪心求解算法求解速度较快,但贪心解的质量却有待提高。轮转贪心策略是在不增加贪心算法时间复杂度的前提下提升贪心解的质量,且通过实验研究表明能有效增强一些NP难度问题效果的贪心算法。本文将轮转贪心策略求解正影响支配集的2个贪心算法进行融合来提升贪心算法解的质量,提出相应的轮转贪心算法。实验表明,在典型的真实社交网络实例上,与原有贪心算法相比,本文的轮转贪心算法所获解的质量有一定的提高。     

一种求解图着色问题的蚁群遗传算法

遗传算法在图着色问题上已经得到广泛的应用,但对于顶点数较多的图,使用此类算法进行着色的结果就显得不够理想,运行效率也不够高。由于遗传算法具有全局收敛性,蚁群算法具有局部收敛性,因此,将遗传算法和蚁群搜索算法融合,提出一种新的解决图着色问题的蚁群遗传算法。该算法先利用蚁群算法快速地为遗传算法搜索到较好的初始解,然后利用遗传算法进一步遗传优化,同时在优化解上加强信息素强度,并反馈给蚁群搜索。实验结果表明,改进的算法在解决顶点数较大的图着色问题上有明显的优势。     

物种生灭算法的改进策略

物种生灭算法（Species Explode and Deracinate Algorithm，SEDA）是一种简单、高效的群智能优化算法。为了进一步提高SEDA算法的寻优速度、解的质量，首先，通过一种无排序筛选幸存物种的递归算法，提出了基于递归筛选的SEDA算法，减少了SEDA算法的时间复杂度，提高了算法的寻优速度；其次，通过引入衍生趋势的方法，提出了基于衍生趋势的SEDA算法，提高了SEDA算法对复杂、难以寻优的优化问题解的质量。三个测试函数的仿真结果表明，改进的方法具有更小的时间复杂度，能够有效改善SEDA算法解的质量。     

混合启发式算法在排课问题上的应用

对排课问题做出了形式化描述,提出了一种用于排课的混合启发式算法,该算法合并使用了模拟退火和迭代局部搜索两种算法。先依据图着色算法产生初始可行解,然后应用模拟退火算法寻找最优解,为使算法更好地跳出局部最优,实现全局搜索,在模拟退火算法应用过程中,迭代使用两个邻域,标准邻域和双Kempe链邻域。实验结果表明,此算法能够很好地提高解的质量。     

有向基因组移位排序问题的O(n2)快速算法

有向基因组移位排序问题在计算生物学研究中占有重要位置．以前最好的算法时间复杂度为O(n^2logn)．该文给出一个有向基因组移位排序的新多项式算法，将移位排序的时间复杂度改进为O(n^2)．算法改进的关键在于找到一种寻找有效合理移位的新方法，通过在最小子排列中删除无关顶点确定一个合理移位是否有效，从而将寻找一个有效移位的时间复杂度改进为O(n)，总时间复杂度由此降为O(n^2)．     

基于变异和启发式选择的蚁群优化算法

为了解决传统蚁群算法求解TSP问题的求解时间较长、易于局部收敛的问题,提出了一种基于变异和启发式选择的蚁群优化算法。利用较优路径中城市相互之间的邻接特点,避免了大范围搜索求解,使得能具有较好的初始解,将算法的时间复杂度大大降低;同时为了加快算法的收敛速度,对于路径的启发式选择进行重新定义;引入变异机制,充分利用2．交换法简洁高效的特点,既提高了变异效率,也改进了变异质量。实验结果证明,在一些经典TSP问题上新算法表现出很好的性能。     

图着色问题的一个最小冲突权值学习算法

图着色问题(GCP)是NP完全问题．近年来求解GCP的启发式局部搜索算法引起人们的关注,GSAT是最著名的局部搜索算法之一．许多局部搜索算法引入跳出局部极小的机制来提高搜索效率,权值学习是一种被广泛采用的方式之一．我们从一些权值学习局部搜索算法抽象出一个通用的权值学习算法(SWLA),进一步把SWLA和GSAT相结合提出了最小冲突权值学习算法(MCWLA),算法还应用还原策略和“权值交叉”算子来提高搜索后期的效率．算法在求解一些难解测试范例时显示出较高的效率,能求得GSAT及SWLA无法求得的最优解．     

基于IMOM和IBOHM启发式策略的扩展规则算法

基于扩展规则的方法是一种定理证明方法.在IER(improved extension rule)扩展规则算法的基础上,提出了IMOM(improved maximum occurrences on clauses of maximum size)和IBOHM(improved BOHM)启发式策略,并将两种启发式策略用于IER算法中,有指导性地选择限定搜索空间的子句,设计并实现了算法IMOMH_IER和IBOHMH_IER.实验结果表明,由于这两种启发式策略能够选择较为合适的搜索空间,可以尽快地判定出原问     

基于拟人策略的高校排课算法

For the university timetabling problem that is NP-hard, some new strategies of tackling it are proposed,and two heuristic algorithms based on personification strategies are presented, which outperform the known straightforward heuristic algorithms in the quality of solution. The experimental results show that our algorithms are practical.     

求图符号控制数的完全算法研究

确定图的符号控制数是NP-难度的问题。针对求解该问题的完全算法即能求得精确最优解的算法进行了研究,提出了几个启发式的限界策略,给出了两个完全算法:回溯算法和A算法。计算实验表明,针对随机产生的问题实例,用这两个算法求解时所生成的结点数目还不到其状态空间树中结点总数目的千分之五。对这两个算法也进行了比较。     

A MOS-based dynamic memetic differential evolution algorithm for continuous optimization: a scalability test

Continuous optimization is one of the areas with more activity in the field of heuristic optimization. Many algorithms have been proposed and compared on several benchmarks of functions, with different performance depending on the problems. For this reason, the combination of different search strategies seems desirable to obtain the best performance of each of these approaches. This contribution explores the use of a hybrid memetic algorithm based on the multiple offspring framework. The proposed algorithm combines the explorative/exploitative strength of two heuristic search methods that separately obtain very competitive results. This algorithm has been tested with the benchmark problems and conditions defined for the special issue of the Soft Computing Journal on Scalability of Evolutionary Algorithms and other Metaheuristics for Large Scale Continuous Optimization Problems. The proposed algorithm obtained the best results compared with both its composing algorithms and a set of reference algorithms that were proposed for the special issue.     

An exact algorithm with learning for the graph coloring problem

Given an undirected graph G=(V,E), the Graph Coloring Problem (GCP) consists in assigning a color to each vertex of the graph G in such a way that any two adjacent vertices are assigned different colors, and the number of different colors used is minimized. State-of-the-art algorithms generally deal with the explicit constraints in GCP: any two adjacent vertices should be assigned different colors, but do not specially deal with the implicit constraints between non-adjacent vertices implied by the explicit constraints. In this paper, we propose an exact algorithm with learning for GCP which exploits the implicit constraints using propositional logic. Our algorithm is compared with several exact algorithms among the best in the literature. The experimental results show that our algorithm outperforms other algorithms on many instances. Specifically, our algorithm allows to close the open DIMACS instance 4-Fullins_5.     

通过八数码问题比较搜索算法的性能

搜索算法的核心在于搜索策略的制定.一般的搜索算法采用无信息指导的搜索策略,如深度优先搜索(DFS)和宽度优先搜索(BFS),还有一些搜索算法采用了启发式信息指导的搜索策略,如A*算法.不同的搜索策略会使得搜索算法的性能有很大的差异.使用以上3种搜索算法实现八教码问题的求解,分析和比较三者所表现出来的性能,同时指出3种搜索算法的特点和应用范围,最后给出分析结论以指导开发和使用更加高效的搜索策略.     

Strategies in heuristic search

Real-valued heuristic functions have been extensively used as a means for constraining search in combinatorially large problem spaces. In this paper we look at an alternative approach, called strategic search, in which heuristic information is expressed in the form of problem specific strategies. A strategy is considered to be a (possibly partial) function which for a given state in some problem domain returns sequences of states over the problem domain. The strategy is intended to guide one towards a goal state, but there is no guarantee of success. Strategic search generates a search graph by following some strategy or set of strategies, backtracking to previous choice points when the current strategy fails. We first examine algorithms for performing strategic search using both deterministic and non-deterministic (multiple) strategies. Some examples are given which indicate that strategic search can outperform standard heuristic search methods. We then describe some algorithms which are shown to be admissible when the strategy satisfies certain conditions. The construction of strategies is also considered, and means for acquiring strategic knowledge both from analogous problems and from example execution traces are described. Finally, we indicate how these techniques can be extended to hierarchically organized problem spaces and show how meta-level strategies can be used to guide the application of object level strategies.     

A comparative runtime analysis of heuristic algorithms for satisfiability problems

The satisfiability problem is a basic core NP-complete problem. In recent years, a lot of heuristic algorithms have been developed to solve this problem, and many experiments have evaluated and compared the performance of different heuristic algorithms. However, rigorous theoretical analysis and comparison are rare. This paper analyzes and compares the expected runtime of three basic heuristic algorithms: RandomWalk, (1+1) EA, and hybrid algorithm. The runtime analysis of these heuristic algorithms on two 2-SAT instances shows that the expected runtime of these heuristic algorithms can be exponential time or polynomial time. Furthermore, these heuristic algorithms have their own advantages and disadvantages in solving different SAT instances. It also demonstrates that the expected runtime upper bound of RandomWalk on arbitrary k-SAT (k?3) is O(n(k−1)), and presents a k-SAT instance that has Θ(n(k−1)) expected runtime bound.     

Improved methods for scheduling flexible manufacturing systems based on Petri nets and heuristic search

This paper proposes and evaluates two improved Petri net （PN）-based hybrid search strategies and their applications to flexible manufacturing system （FMS） scheduling. The algorithms proposed in some previous papers, which combine PN simulation capabilities with A＊ heuristic search within the PN reachability graph,may not find an optimum solution even with an admissible heuristic function. To remedy the defects an improved heuristic search strategy is proposed, which adopts a different method for selecting the promising markings and reserves the admissibility of the algorithm. To speed up the search process, another algorithm is also proposed which invokes faster termination conditions and still guarantees that the solution found is optimum. The scheduling results are compared through a simple FMS between our algorithms and the previous methods. They are also applied and evaluated in a set of randomly-generated FMSs with such characteristics as multiple resources and alternative routes.