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.

Local Search Heuristics for NFA State Minimization Problem

In the present paper we introduce new heuristic methods for the state minimization of nondeterministic finite automata. These methods are based on the classical Kameda-Weiner algorithm joined with local search heuristics, such as stochastic hill climbing and simulated annealing. The description of the proposed methods is given and the results of the numerical experiments are provided.

Nesting and Berth Allocation by an Expert System Using Heuristic Search

Nesting is a common problem in industries such as shipbuilding, auto-maker, clothing, shoe-making, and furniture, in which various parts are cut off from a stock or stocks while minimizing the wastes or maximizing the utilization of the stock. Berth allocation at seaside is also considered one form of two dimensional nesting problems, in which a ship is assigned a location for service during a certain time slot. This paper presents an expert system using a heuristic search method for nesting problems. The parts and stocks are represented by pixels with which utility function is used to evaluate current state in search tree. The system is developed in CLIPS, an expert system shell and applied to various example problems with different constraints and to a berth allocation example to illustrate its applicability under different conditions.

Applying Heuristic Search for Distributed Software Performance Enhancement

Software reverse engineering and reengineering techniques are most often applied to reconstruct the software archi-tecture with respect to quality constraints, or non-functional requirements such as maintainability or reusability. In this paper, the performance improvement of distributed software is modeled as a search problem that is solved by heuristic search algorithms such as genetic search methods. To achieve this, firstly, all aspects of the distributed execution of a software is specified by an analytical performance evaluation function that not only evaluates the current deployment of the software from the performance perspective but also can be applied to propose the near-optimal object deploy-ment for that software. This analytical function is applied as the Heuristic search objective function. In this paper a novel statement reordering method is also presented which is used to generate the search objective function such that the best solution in the search space can be found.

A Heuristic Search Approach to Multidimensional Scaling

This research effort presents an approach to accomplish Multidimensional Scaling (MDS) via the heuristic approach of Simulated Annealing. Multidimensional scaling is an approach used to convert matrix-based similarity (or dissimilarity data) into spatial form, usually via two or three dimensions. Performing MDS has several important applications—Geographic Information Systems, DNA Sequencing, and Marketing Research are just a few. Traditionally, classical MDS decomposes the similarity or dissimilarity matrix into its eigensystem and uses the eigensystem to calculate spatial coordinates. Here, a heuristic search-based approach is used to find coordinates from a dissimilarity matrix that minimizes a cost function. The proposed methodology is used over a variety of problems. Experimentation shows that the presented methodology consistently outperforms solutions obtained via the classical MDS approach, and this approach can be used for other important applications.

Meta-heuristic算法研究进展

对模拟退火、遗传算法和禁忌搜索法等代表性 meta-heuristic算法在理论与应用方面的研究进行综述 ,探讨算法结构和研究体系上的统一性 ,并归纳指出其发展方向。

A Fast Insertion Tabu Search with Conflict-Avoidance Heuristic for the Multisatellite Multimode Crosslink Scheduling Problem

An agile earth-observing satellite equipped with multimode cameras capable of transmitting observation data to other satellites is developed to rapidly respond to requests with multiple observation modes.This gives rise to the Multisatellite Multimode Crosslink Scheduling(MMCS)problem,which involves allocating observation requests to agile satellites,selecting appropriate timing and observation modes for the requests,and transmitting the data to the ground station via the satellite communication system.Herein,a mixed integer programming model is introduced to include all complex time and operation constraints.To solve the MMCS problem,a two-stage heuristic method,called Fast insertion Tabu Search with Conflict-avoidance(FTS-C)heuristic,is developed.In the first stage,a conflict-avoidance insertion algorithm is designed to generate a high-quality initial solution by considering the requests transmission and download.Further,the tabu search-based second stage optimizes the initial solution.Finally,an extensive empirical study based on a real-world situation demonstrates that FTS-C can generate a solution with higher quality in less time than other state-of-the-art algorithms and the CPLEX solver.

基于改进蚁群算法的移动机器人路径规划

针对传统蚁群算法在移动机器人路径规划中存在搜索盲目性、收敛速度慢及路径转折点多等问题,提出了一种基于改进蚁群算法的移动机器人路径规划算法。首先,利用跳点搜索(Jump Point Search,JPS)算法不均匀分配初始信息素,降低蚁群前期盲目搜索的概率;然后,引入切比雪夫距离加权因子和转弯代价改进启发函数,提高算法的收敛速度、全局路径寻优能力和搜索路径的平滑程度;最后,提出一种新的信息素更新策略,引入自适应奖惩因子,自适应调整迭代前、后期的信息素奖惩因子,保证了算法全局最优收敛。实验仿真结果表明,在不同地图环境下,与现有文献结果对比,该算法可以有效地缩短路径搜索的迭代次数和最优路径长度,并提高路径的平滑程度。

城市轨道交通列车加开计划编制模型研究

本文主要研究城市轨道交通在计划编制阶段由于客流不均衡需要在初始运行图加开列车的问题,在确保列车运行安全降低运营成本的前提下合理地加开列车实现运输能力的灵活配置。将列车运行过程形式化描述为事件-活动网络,构建了分时段多目标优化列车加开计划编制模型,提出了启发式决策规则与禁忌搜索算法相结合的两阶段求解算法。结合地铁运行实际数据,在高峰时段和平峰时段分别构建不同算例场景,验证了模型和算法的可行性和有效性。

基于邻域互信息的组合预测最优子集选择算法

为在候选模型集中高效地选择时间序列组合预测的最优子集,提出一种CSPSO-NMI-MRMR最优子集选择算法。利用邻域互信息(neighborhood mutual information, NMI)度量相关性和冗余度,避免数值型数据的离散化,按最大相关最小冗余原则(minimal redundancy and maximal relevance, MRMR)筛选最优子集;邻域互信息中的邻域参数与子集选择效果密切相关,采用CSPSO算法寻找最优邻域参数,充分利用布谷鸟算法(cuckoo search, CS)和粒子群优化算法(particle swarm optimization, PSO)的优势,兼顾搜索效率和全局搜索能力;在寻参过程中设计一种淘汰策略,优化邻域参数的寻优区间并淘汰部分单模型,减少计算量。仿真结果表明,所提方法在预测精度、运行时间和稳健性上效果更优。

一种带时间窗和容量约束的车辆路线问题及其TabuSearch算法

本文提出一种带时间窗和容量约束的车辆路线问题 (CVRPTW ) ,并利用TabuSearch快速启式算法 ,针对Solomon提出的几个标准问题 ,快捷地得到了优良的数值结果。

考虑伤员健康状态变化的紧急医疗救援路径优化

重大突发事件造成的伤员人数往往超出现场急救、转运和处理能力,邻近医院仅能提供有限的医疗救援服务,高效地转运不同受伤程度的伤员成为紧急医疗救援的关键。以全部伤员的健康状态总和最大为目标,考虑伤员病情随时间动态恶化的程度,提出了一种救护车与社会车辆共同救援的多车场、多车型、多周期紧急医疗救援路径优化模型,并以成都市的部分安置点和医院的实际数据为例,采用启发式邻域搜索算法对模型进行求解,验证了模型的有效性。结果表明:采用共同救援模式可有效提高伤员整体健康水平。研究结果可为重大突发事件下的伤员转运及通道保障提供决策参考。

Scatter search算法求解无能力约束生产批量计划问题

多级生产批量计划(multilevel lot-sizing,MLLS)问题是物料需求计划(material requirements planning,MRP)系统中的关键问题,已被证明是NP难问题。Scattersearch(SS)算法是一种亚启发式算法,其应用范围已涉及优化领域中的许多NP难问题。扩展了SS算法的应用范围,采用结合变异算子的混合SS算法(hybrid scatter search,HSS)对具有小规模和中规模的装配结构无能力约束MLLS问题进行了求解。仿真实验表明HSS算法能够有效地求解MLLS问题,其求解结果明显优于遗传算法的求解结果。

基于智能规划的多智能体强化学习算法

目前深度强化学习算法在不同应用领域中已经取得诸多成果,然而在多智能体任务领域中,往往面临大规模的具有稀疏奖励的非稳态环境,低探索效率问题仍是一大挑战。由于智能规划能够根据任务的初始状态和目标状态快速制定出决策方案,该方案能够作为各智能体的初始策略,并为其探索过程提供有效指导,因此尝试将智能规划与多智能体强化学习进行结合求解,并且提出统一模型UniMP(a Unified model for Multi-agent Reinforcement Learning and AI Planning)。在此基础上,设计并建立相应的问题求解机制。首先,将多智能体强化学习任务转化为智能决策任务;其次,对其执行启发式搜索,以得到一组宏观目标,进而指导强化学习的训练,使得各智能体能够进行更加高效的探索。在多智能体即时战略对抗场景StarCraftⅡ的各地图以及RMAICS战车模拟对战环境下进行实验,结果表明累计奖励值和胜率均有显著提升,从而验证了统一模型的可行性、求解机制的有效性以及所提算法灵活应对强化学习环境突发情况的能力。

两种高效局部搜索算法求解RB模型实例

RB(revised B)模型是一种在约束可满足问题中具备精确相变增长域的随机实例模型,提出两种高效的启发式局部搜索算法用于解决RB模型生成的大值域约束可满足问题。首先为基于权重指导搜索的W-MCH算法,该算法通过约束判断和违反约束数计分来进行搜索,并引入了基于约束违反概率的权重计算公式,根据其关联的约束权重进行修正,再对变量进行迭代调整。然后提出最小化值域的MDMCH算法,该算法通过记录违反约束和逐步消除已违反约束变量的启发式策略来减少搜索空间,并在最小化后的变量域内重新校准变量赋值,进而有效提高算法的收敛速度。此外,还提出了融入模拟退火策略的WSCH和MDSCH算法,这两种算法都能根据变量的表征特点对变量域进行针对性的搜索。实验结果表明,与多种启发式算法相比,这两种算法在精度与时间效率方面均呈现明显提升,在复杂难解的实例中能够提供高效的求解效率,验证了算法的有效性和优越性。

具有混合策略的樽海鞘群特征选择算法

近年来,随着计算机和数据库技术的快速发展,大规模数据集迅速增长,利用特征选择技术来筛选信息量大的特征已经变得非常重要。本文提出了一种具有混合策略的樽海鞘群特征选择算法(salp swarm feature selection algorithm with hybrid strategy,HS-SSA)。首先,本文生成一张基于互信息的排序表,并由排序表提出了新的初始化策略。其次,提出一个新颖的并且有条件调用的动态搜索算法。最后在位置更新上结合瞬态搜索算法(transient search algorithm,TSO),改进勘探和开发步骤的效率,增加解空间的灵活性和多样性,从而使算法能够快速定位到全局最优位置。为了验证算法的性能,实验选取14个UCI的数据集,并且与樽海鞘群算法(SSA)以及近几年樽海鞘群的改进算法等多种优化算法进行比较,结果表明HS-SSA在特征选择上具有更强的竞争力。

基于最优邻域搜索粒子群的低轨卫星通信任务规划方法

针对低轨卫星通信中的任务规划问题,提出了一种基于最优邻域搜索粒子群优化(Particle Swarm Optimization,PSO)群算法的任务规划方法。引入最优近邻搜索,通过最优粒子间的差分值来促进局部搜索,设计了惯性权值、社会和自我学习因子的优化方式,最终能够高效求解低轨卫星通信星座中多转发器与多任务的组合优化问题,用以应对低轨卫星过境时间限制和链路切换导致的时间段离散问题,并使得算法前期具有更强探索全局最优和后期快速收敛的能力。实验验证结果表明,该方法能够在低轨卫星中的约束条件下,有效提高卫星平均资源占用率(Average Occupancy Percentage,AOP)的同时减少算法收敛的迭代次数,显著降低运行时间开销。

智能化测量学教学辅助系统与组卷策略的设计及研究

针对当前计算机教学辅助系统中存在的组卷难度和题型比例不合理等问题,以测量学课程为例,提出了多约束条件的组合优化模型,解决了自动化组卷的多指标参数问题,为实现科学的组卷策略提供参考依据。该模型综合考虑试卷的总分、难度、曝光率、题型比例、章节知识量、培养目标等多个方面的要求进行量化加权,建立了智能化组卷的总约束方程,构建了多参数约束的组合优化模型。采用计算机模拟仿真的方法建立了题库,分析了三种启发式搜索算法求解模型的解算精度和效率。结果表明,利用遗传算法实现的自动化组卷的整体精度和效率更高,在总分、难度、曝光率、题型比例、章节知识量和培养目标方面的平均偏差分别为0.2%.0.074、0.1%6.1%、8.2%和9.6%,迭代次数在230次以内基本能够达到最优解。

求解最小双连通支配集问题的变邻域禁忌搜索算法

针对经典NP难优化问题——最小双连通支配集问题,提出了一种元启发式求解算法——变邻域禁忌搜索算法。算法将原优化问题的求解转换为一系列判定问题——k双连通支配集问题的求解,使用两种邻域结构更加有效地覆盖解空间,同时使用扰动及禁忌机制帮助算法跳出局部最优陷阱。通过与现有文献中的精确算法、启发式算法在国际文献公开的38个双连通图算例上的实验对比,结果表明变邻域禁忌搜索算法能够有效求解最小双连通支配集问题,可求得所有公开算例的最优解,并且在稠密图中计算效率明显优先于其他算法。

基于多顶点替换策略的迭代局部搜索算法解决覆盖推销员问题

覆盖推销员问题(Covering Salesman Problem,CSP)是著名的旅行商问题的一个变体,是NP难问题。给定一组顶点和每个顶点相关联的预定覆盖半径,CSP的目标是在顶点子集上找到一个最短长度的哈密顿回路,使每个顶点被访问或者在被访问顶点的覆盖范围内。为提升搜索候选顶点集的质量,提出一种基于多顶点替换的搜索策略,并将该策略引入到迭代局部搜索算法解决CSP。所提CSP算法通过扰动过程和改进过程的迭代探索邻域最优解,其中扰动过程将搜索发散到未探索的区域,改进过程提升解的质量。实验结果表明,多顶点替换方法相比“移出-重新插入”过程可以获得更高质量的候选顶点集。所提CSP算法在寻优的正确率上取得了不错的成效,尽管运行速度与其他启发式算法相比有差距,但可以在合理的运行时间内解决CSP。