混合流水车间插单重调度的超启发式遗传算法

针对带有紧急订单的混合流水车间插单重调度问题,提出了一种双层编码的超启发式遗传算法。针对混合流水车间具有的订单排序和机器选择的双决策特征,在算法低层设计双层编码方案,在个体中表示订单排序和机器选择两类信息,对应一个唯一调度解,进而提出了12种排序和选择启发式对个体进行迭代优化;在算法高层采用自适应遗传算法,用来确定订单排序启发式和机器选择启发式的操作组合以及各组合执行的次序,并设计了自适应变异算子来优化算法的有效性。大规模数据实验的结果表明,所提算法具有很好的求解质量和求解效率。     

超启发式交叉熵算法求解模糊分布式流水线绿色调度问题

针对实际生产过程中普遍存在的加工时间不确定性,采用模糊数表示工件的加工时间,以同时最小化模糊最大完工时间和模糊总能耗为优化目标,建立模糊分布式流水线绿色调度问题(green distributed permutation flow-shop scheduling problem with fuzzy processing time,GDPFSP_FPT)的模型,进而提出一种超启发式交叉熵算法(hyper-heuristic cross-entropy algorithm,HHCE)进行求解.首先,HHCE采用一种新颖的三角模糊数排序准则合理计算个体的目标函数值,可在算法搜索过程中较准确发现优质解区域;其次,HHCE在高层利用基于贡献率的评价方法确定8种特定邻域操作所构成的各排列的优劣,同时采用交叉熵(cross-entropy,CE)方法学习较优排列的信息并生成新排列,进而在低层把高层生成的每个排列作为一种启发式算法,对低层相应个体执行一系列邻域操作,以实现对问题解空间较多不同区域的搜索;然后,HHCE将基于非关键路径的节能策略用于对低层每代种群中的较优个体执行局部搜索,从而进一步提高算法获取低能耗非劣个体或解的能力;最后,仿真实验与算法对比表明,HHCE可有效求解GDPFSP_FPT.     

超启发式人工蜂群算法求解多场景鲁棒分布式置换流水车间调度问题

本文考虑现实中广泛存在的加工时间不确定的分布式置换流水车间调度问题(DPFSP),研究如何建立问题模型和设计求解算法,方可确保算法最终获得的解在多个典型DPFSP场景下,均具有能满足客户期望的较小优化目标值(即makespan值).在问题建模方面,首先,采用场景法构建多个不同典型场景以组成场景集(每个场景对应1个具有不同加工时间的DPFSP),并设定合适的makespan值作为场景阈值,用于在评价问题解时从场景集中动态筛选出“坏”场景子集;其次,在常规优化目标makespan的基础上,结合“坏”场景子集概念提出可实现鲁棒调度的新型优化目标,用于引导算法每代加强对当前“坏”场景子集中每个DPFSP场景对应解空间的搜索;然后,结合所提的新型优化目标,建立基于多场景的鲁棒DPFSP (MSRDPFSP).在算法设计方面,提出一种超启发式人工蜂群算法(HHABC)对MSRDPFSP进行求解. HHABC分为高、低两层结构,其中低层设计6种启发式操作(HO),高层采用人工蜂群算法控制和选择低层HOs来不断生成新的混合启发式算法,从而实现在不同场景对应解空间中的较深入搜索.在不同规模测试问题上的仿...     

启发式算法求解最大团问题研究

最大团问题(maximum clique problem,MCP)是图论中的一个经典组合优化问题,也是一类NP完全问题,在国际上已有广泛地研究,国内研究刚刚起步.给出了最大团问题的基本定义和其数学描述;阐述了该问题的研究进展;分析和研究了求解该问题的各种典型启发式算法,包括算法的介绍、算法求解最大团问题的基本思路、特点及性能;最后介绍了测试这些启发式算法性能的测试基准图.     

超启发式交叉熵算法求解分布式装配柔性作业车间调度问题

本文针对一类新型两阶段分布式装配柔性作业车间调度问题(DAFJSP),建立问题模型,以最小化最大完工时间为优化目标并提出一种超启发式交叉熵算法(HHCEA)进行求解.首先,设计基于工序序列、工厂分配和产品序列的三维向量编码规则和结合贪婪策略的解码规则,同时提出4种启发式方法以提高初始解的质量.然后,设计高低分层结构的HHCEA,高层为提高对搜索方向的引导性,采用交叉熵算法(CEA)学习和积累优质排列的信息,其中各排列由结合问题特点设计的11种启发式操作(即11种有效的邻域操作)构成;低层为增加在解空间中的搜索深度,将高层确定的每个排列中的启发式操作依次重复执行指定次数并在执行过程中加入基于模拟退火的扰动机制,以此作为一种新的启发式方法执行搜索.最后,通过仿真实验与算法对比验证HHCEA可有效求解DAFJSP.     

基于规则的个性化课表生成算法

提出并实现了一种基于规则的个性化课表生成算法。该算法构建了排课过程的启发式规则和规则应用策略,以个性化需求为特征的数据结构为初始状态,通过启发、优化和回溯等过程,求解满足要求的状态解并生成相应课表。应用表明该算法设计合理,运算速度快。     

超启发式分布估计算法求解带软时间窗的同时取送货车辆路径问题

本文针对带软时间窗的同时取送货车辆路径问题(VRPSPDSTW),以最小化车辆行驶总里程和最大化服务准时率为优化目标,提出一种超启发式分布估计算法(HHEDA)进行求解.全局搜索阶段,首先,提出3种启发式规则生成初始个体,以确保初始种群的质量和分散性;其次,根据问题特点,构造3个概率矩阵分别学习和积累优质解的排序信息、客户间的距离信息和捆绑信息,并通过采样概率矩阵生成新个体,以增强算法全局搜索发现解空间中优质区域的能力.局部搜索阶段,将11种邻域操作组成备选集合,进而设计学习型超启发式局部搜索(LHHLS),用于动态选择备选集合中的部分邻域操作构成多种新的有效启发式算法,以执行对解空间中优质区域的深入搜索.最后,仿真实验和算法比较验证了HHEDA的有效性.     

三阶段优化算法求解带三维装载约束的MDVRP北大核心CSCD

对带三维装载约束的多车场车辆路径问题,以最小化车辆行驶总里程为优化目标,建立问题模型,并提出一种三阶段优化算法进行求解。第一阶段设计带循环平衡的K-medoids聚类算法,将原问题分解成多个带三维装载约束限制的车辆路径子问题。第二阶段提出一种双层结构的超启发式蚁群算法用于求解各子问题,以确定各车辆的配送路径。在该算法中,低层设计9种启发式操作,并将其所构成的排列作为高层个体;同时,高层采用蚁群算法更新高层个体,以引导算法搜索方向。第三阶段以第二阶段所得阶段解作为初始解,设计组合启发式装箱算法对带容积约束的装箱过程进行优化,进而将第二、三阶段确定的解合并为原问题的解。最后,仿真实验和算法比较验证了所提算法的有效性。     

车辆路径问题的轻鲁棒优化模型与算法

针对不确定旅行时间下的车辆路径问题,以总变动成本最小为优化目标,建立了一种轻鲁棒优化模型,提出了一种针对问题特征的超启发式粒子群算法.在算法中,利用基于图论中深度优先搜索的初始化策略加快算法的早期收敛速度,引入基于均衡策略的启发式规则变换方式来提高算法的寻优能力,重新设计的粒子更新公式确保生成低层构造算法的有效性.实验...     

求解二维装箱问题的强化学习启发式算法

二维带形装箱问题是一个经典的NP-hard的组合优化问题,该问题在实际的生活和工业生产中有着广泛的应用.研究该问题,对企业节约成本、节约资源以及提高生产效率有着重要的意义.提出了一个强化学习求解算法.新颖地使用强化学习为启发式算法提供一个初始的装箱序列,有效地改善启发式冷启动的问题.该强化学习模型能进行自我驱动学习,仅使用启发式计算的解决方案的目标值作为奖励信号来优化网络,使网络能学习到更好的装箱序列.使用简化版的指针网络来解码输出装箱序列,该模型由嵌入层、解码器和注意力机制组成.使用Actor-Critic算法对模型进行训练,提高了模型的效率.在714个标准问题实例和随机生成的400个问题实例上测试提出的算法,实验结果显示：提出的算法能有效地改善启发式冷启动的问题,性能超过当前最优秀的启发式求解算法.     

A new hyper-heuristic as a general problem solver: an implementation in HyFlex

This study provides a new hyper-heuristic design using a learning-based heuristic selection mechanism together with an adaptive move acceptance criterion. The selection process was supported by an online heuristic subset selection strategy. In addition, a pairwise heuristic hybridization method was designed. The motivation behind building an intelligent selection hyper-heuristic using these adaptive hyper-heuristic sub-mechanisms is to facilitate generality. Therefore, the designed hyper-heuristic was tested on a number of problem domains defined in a high-level framework, i.e., HyFlex. The framework provides a set of problems with a number of instances as well as a group of low-level heuristics. Thus, it can be considered a good environment to measure the generality level of selection hyper-heuristics. The computational results demonstrated the generic performance of the proposed strategy in comparison with other tested hyper-heuristics composed of the sub-mechanisms from the literature. Moreover, the performance and behavior analysis conducted for the hyper-heuristic clearly showed its adaptive characteristics under different search conditions. The principles comprising the here presented algorithm were at the heart of the algorithm that won the first international cross-domain heuristic search competition.     

An evolutionary-based hyper-heuristic approach for the Jawbreaker puzzle

In this paper a hyper-heuristic algorithm is designed and developed for its application to the Jawbreaker puzzle. Jawbreaker is an addictive game consisting in a matrix of colored balls, that must be cleared by popping sets of balls of the same color. This puzzle is perfect to be solved by applying hyper-heuristics algorithms, since many different low-level heuristics are available, and they can be applied in a sequential fashion to solve the puzzle. We detail a set of low-level heuristics and a global search procedure (evolutionary algorithm) that conforms to a robust hyper-heuristic, able to solve very difficult instances of the Jawbreaker puzzle. We test the proposed hyper-heuristic approach in Jawbreaker puzzles of different size and difficulty, with excellent results.     

Choice function based hyper-heuristics for multi-objective optimization

A selection hyper-heuristic is a high level search methodology which operates over a fixed set of low level heuristics. During the iterative search process, a heuristic is selected and applied to a candidate solution in hand, producing a new solution which is then accepted or rejected at each step. Selection hyper-heuristics have been increasingly, and successfully, applied to single-objective optimization problems, while work on multi-objective selection hyper-heuristics is limited. This work presents one of the initial studies on selection hyper-heuristics combining a choice function heuristic selection methodology with great deluge and late acceptance as non-deterministic move acceptance methods for multi-objective optimization. A well-known hypervolume metric is integrated into the move acceptance methods to enable the approaches to deal with multi-objective problems. The performance of the proposed hyper-heuristics is investigated on the Walking Fish Group test suite which is a common benchmark for multi-objective optimization. Additionally, they are applied to the vehicle crashworthiness design problem as a real-world multi-objective problem. The experimental results demonstrate the effectiveness of the non-deterministic move acceptance, particularly great deluge when used as a component of a choice function based selection hyper-heuristic.     

Parallel hyper heuristic algorithm based on reinforcement learning for the corridor allocation problem and parallel row ordering problem

Hyper heuristics is a relatively new optimisation algorithm. Numerous studies have reported that hyper heuristics are well applied in combinatorial optimisation problems. As a classic combinatorial optimisation problem, the row layout problem has not been publicly reported on applying hyper heuristics to its various sub-problems. To fill this gap, this study proposes a parallel hyper-heuristic approach based on reinforcement learning for corridor allocation problems and parallel row ordering problems. For the proposed algorithm, an outer layer parallel computing framework was constructed based on the encoding of the problem. The simulated annealing, tabu search, and variable neighbourhood algorithms were used in the algorithm as low-level heuristic operations, and Q-learning in reinforcement learning was used as a high-level strategy. A state space containing sequences and fitness values was designed. The algorithm performance was then evaluated for benchmark instances of the corridor allocation problem (37 groups) and parallel row ordering problem (80 groups). The results showed that, in most cases, the proposed algorithm provided a better solution than the best-known solutions in the literature. Finally, the meta-heuristic algorithm applied to three low-level heuristic operations is taken as three independent algorithms and compared with the proposed hyper-heuristic algorithm on four groups of parallel row ordering problem instances. The effectiveness of Q-learning in selection is illustrated by analysing the comparison results of the four algorithms and the number of calls of the three low-level heuristic operations in the proposed method.     

Hyper-heuristics with low level parameter adaptation

Recent years have witnessed the great success of hyper-heuristics applying to numerous real-world applications. Hyper-heuristics raise the generality of search methodologies by manipulating a set of low level heuristics (LLHs) to solve problems, and aim to automate the algorithm design process. However, those LLHs are usually parameterized, which may contradict the domain independent motivation of hyper-heuristics. In this paper, we show how to automatically maintain low level parameters (LLPs) using a hyper-heuristic with LLP adaptation (AD-HH), and exemplify the feasibility of AD-HH by adaptively maintaining the LLPs for two hyper-heuristic models. Furthermore, aiming at tackling the search space expansion due to the LLP adaptation, we apply a heuristic space reduction (SAR) mechanism to improve the AD-HH framework. The integration of the LLP adaptation and the SAR mechanism is able to explore the heuristic space more effectively and efficiently. To evaluate the performance of the proposed algorithms, we choose the p-median problem as a case study. The empirical results show that with the adaptation of the LLPs and the SAR mechanism, the proposed algorithms are able to achieve competitive results over the three heterogeneous classes of benchmark instances.     

Grammar-based generation of variable-selection heuristics for constraint satisfaction problems

We propose a grammar-based genetic programming framework that generates variable-selection heuristics for solving constraint satisfaction problems. This approach can be considered as a generation hyper-heuristic. A grammar to express heuristics is extracted from successful human-designed variable-selection heuristics. The search is performed on the derivation sequences of this grammar using a strongly typed genetic programming framework. The approach brings two innovations to grammar-based hyper-heuristics in this domain: the incorporation of if-then-else rules to the function set, and the implementation of overloaded functions capable of handling different input dimensionality. Moreover, the heuristic search space is explored using not only evolutionary search, but also two alternative simpler strategies, namely, iterated local search and parallel hill climbing. We tested our approach on synthetic and real-world instances. The newly generated heuristics have an improved performance when compared against human-designed heuristics. Our results suggest that the constrained search space imposed by the proposed grammar is the main factor in the generation of good heuristics. However, to generate more general heuristics, the composition of the training set and the search methodology played an important role. We found that increasing the variability of the training set improved the generality of the evolved heuristics, and the evolutionary search strategy produced slightly better results.     

An investigation on the generality level of selection hyper-heuristics under different empirical conditions

The present study concentrates on the generality of selection hyper-heuristics across various problem domains with a focus on different heuristic sets in addition to distinct experimental limits. While most hyper-heuristic research employs the term generality in describing the potential for solving various problems, the performance changes across different domains are rarely reported. Furthermore, a hyper-heuristic's performance study purely on the topic of heuristic sets is uncommon. Similarly, experimental limits are generally ignored when comparing hyper-heuristics. In order to demonstrate the effect of these generality related elements, nine heuristic sets with different improvement capabilities and sizes were generated for each of three target problem domains. These three problem domains are home care scheduling, nurse rostering and patient admission scheduling. Fourteen hyper-heuristics with varying intensification/diversification characteristics were analysed under various settings. Empirical results indicate that the performance of selection hyper-heuristics changes significantly under different experimental conditions.     

Integrating neural networks and logistic regression to underpin hyper-heuristic search

A hyper-heuristic often represents a heuristic search method that operates over a space of heuristic rules. It can be thought of as a high level search methodology to choose lower level heuristics. Nearly 200 papers on hyper-heuristics have recently appeared in the literature. A common theme in this body of literature is an attempt to solve the problems in hand in the following way: at each decision point, first employ the chosen heuristic(s) to generate a solution, then calculate the objective value of the solution by taking into account all the constraints involved. However, empirical studies from our previous research have revealed that, under many circumstances, there is no need to carry out this costly 2-stage determination and evaluation at all times. This is because many problems in the real world are highly constrained with the characteristic that the regions of feasible solutions are rather scattered and small. Motivated by this observation and with the aim of making the hyper-heuristic search more efficient and more effective, this paper investigates two fundamentally different data mining techniques, namely artificial neural networks and binary logistic regression. By learning from examples, these techniques are able to find global patterns hidden in large data sets and achieve the goal of appropriately classifying the data. With the trained classification rules or estimated parameters, the performance (i.e. the worth of acceptance or rejection) of a resulting solution during the hyper-heuristic search can be predicted without the need to undertake the computationally expensive 2-stage of determination and calculation. We evaluate our approaches on the solutions (i.e. the sequences of heuristic rules) generated by a graph-based hyper-heuristic proposed for exam timetabling problems. Time complexity analysis demonstrates that the neural network and the logistic regression method can speed up the search significantly. We believe that our work sheds light on the development of more advanced knowledge-based decision support systems.     

On the investigation of hyper-heuristics on a financial forecasting problem

Financial forecasting is a really important area in computational finance, with numerous works in the literature. This importance can be reflected in the literature by the continuous development of new algorithms. Hyper-heuristics have been successfully used in the past for a number of search and optimization problems, and have shown very promising results. To the best of our knowledge, they have not been used for financial forecasting. In this paper we present pioneer work, where we use different hyper-heuristics frameworks to investigate whether we can improve the performance of a financial forecasting tool called EDDIE 8. EDDIE 8 allows the GP (Genetic Programming) to search in the search space of indicators for solutions, instead of using pre-specified ones; as a result, its search area has dramatically increased and sometimes solutions can be missed due to ineffective search. We apply 14 different low-level heuristics to EDDIE 8, to 30 different datasets, and examine their effect to the algorithm’s performance. We then select the most prominent heuristics and combine them into three different hyper-heuristics frameworks. Results show that all three frameworks are competitive, and are able to show significantly improved results, especially in the case of best results. Lastly, analysis on the weights of the heuristics shows that there can be a constant swinging among some of the low-level heuristics, which denotes that the hyper-heuristics frameworks are able to ‘know’ the appropriate time to switch from one heuristic to the other, based on their effectiveness.     

A multi-objective hyper-heuristic based on choice function

Hyper-heuristics are emerging methodologies that perform a search over the space of heuristics in an attempt to solve difficult computational optimization problems. We present a learning selection choice function based hyper-heuristic to solve multi-objective optimization problems. This high level approach controls and combines the strengths of three well-known multi-objective evolutionary algorithms (i.e. NSGAII, SPEA2 and MOGA), utilizing them as the low level heuristics. The performance of the proposed learning hyper-heuristic is investigated on the Walking Fish Group test suite which is a common benchmark for multi-objective optimization. Additionally, the proposed hyper-heuristic is applied to the vehicle crashworthiness design problem as a real-world multi-objective problem. The experimental results demonstrate the effectiveness of the hyper-heuristic approach when compared to the performance of each low level heuristic run on its own, as well as being compared to other approaches including an adaptive multi-method search, namely AMALGAM.