Perturbed Decomposition Algorithm applied to the multi-objective Traveling Salesman Problem

Dealing with multi-objective combinatorial optimization, this article proposes a new multi-objective set-based meta-heuristic named Perturbed Decomposition Algorithm (PDA). Combining ideas from decomposition methods, local search and data perturbation, PDA provides a 2-phase modular framework for finding an approximation of the Pareto front. The first phase decomposes the search into a number of linearly aggregated problems of the original multi-objective problem. The second phase conducts an iterative process: aggregated problems are first perturbed then selected and optimized by an efficient single-objective local search solver. Resulting solutions will serve as a starting point of a multi-objective local search procedure, called Pareto Local Search. After presenting a literature review of meta-heuristics on the multi-objective symmetric Traveling Salesman Problem (TSP), we conduct experiments on several instances of the bi-objective and tri-objective TSP. The experiments show that our proposed algorithm outperforms the best current methods on this problem.     

一个基于填充函数变换的对称TSP问题的局部搜索算法

该文提出了求对称TSP问题近优解的填充函数算法。首先，在用局部搜索算法求得对称TSP问题的一个局部极小解后，对该问题作填充函数变换得到一新的组合优化问题，新问题的局部极小解和最优解分别是原问题的局部极小解和最优解，而且在对称TSP问题的目标函数值大于或等于其目标函数当前极小值的区域中，新问题只有一个已知的局部极小解。随后用局部搜索算法求新问题的一个局部极小解，它或者是已知的局部极小解，或者是对称TSP问题的更好的局部极小解。对多个标准实例的计算试验表明，该文所构造的算法优于直接求解对称TSP问题的局部搜索算法。     

Approximating the Pareto curve with local search for the bicriteria TSP(1,2) problem

Local search has been widely used in combinatorial optimization (Local Search in Combinatorial Optimization, Wiley, New York, 1997), however, in the case of multicriteria optimization almost no results are known concerning the ability of local search algorithms to generate “good” solutions with performance guarantee. In this paper, we introduce such an approach for the classical traveling salesman problem (TSP) problem (Proc. STOC’00, 2000, pp. 126–133). We show that it is possible to get in linear time, a -approximate Pareto curve using an original local search procedure based on the 2-opt neighborhood, for the bicriteria TSP(1,2) problem where every edge is associated to a couple of distances which are either 1 or 2 (Math. Oper. Res. 18 (1) (1993) 1).     

Multistart Tabu Search and Diversification Strategies for the Quadratic Assignment Problem

The quadratic assignment problem (QAP) is a well-known combinatorial optimization problem with a wide variety of applications, prominently including the facility location problem. The acknowledged difficulty of the QAP has made it the focus of many metaheuristic solution approaches. In this paper, we show the benefit of utilizing strategic diversification within the tabu search (TS) framework for the QAP, by incorporating several diversification and multistart TS variants. Computational results for an extensive and challenging set of QAP benchmark test problems demonstrate the ability of our TS variants to improve on a classic TS approach that is one of the principal and most extensively used methods for the QAP. We also show that our new procedures are highly competitive with the best recently introduced methods from the literature, including more complex hybrid approaches that incorporate the classic TS method as a subroutine.     

粒子群算法求解旅行商问题程序设计

粒子群优化算法是一种具备全局搜索能力的群集智能优化算法,针对一类离散的、NP完全的组合优化问题——旅行商问题．该文介绍了用粒子群算法求解旅行商问题的改进策略和主要模块的程序设计思想。将算法应用到20个城市的解旅行商问题所得到的结果与遗传算法进行比较,数字仿真与结果比较表明了改进粒子群算法求解该问题的有效性。     

粒子群算法求解旅行商问题程序设计

粒子群优化算法是一种具备全局搜索能力的群集智能优化算法,针对一类离散的、NP完全的组合优化问题——旅行商问题,该文介绍了用粒子群算法求解旅行商问题的改进策略和主要模块的程序设计思想。将算法应用到20个城市的解旅行商问题所得到的结果与遗传算法进行比较,数字仿真与结果比较表明了改进粒子群算法求解该问题的有效性。     

一种改进的求解TSP混合粒子群优化算法

为解决粒子群算法在求解组合优化问题中存在的早熟性收敛和收敛速度慢等问题,将粒子群算法与局部搜索优化算法结合,可抑制粒子群算法早熟收敛问题,提高粒子群算法的收敛速度。通过建立有效的局部搜索优化算法所需借助的参照优化边集,提高了局部搜索优化算法的求解质量和求解效率。新的混合粒子群算法高效收敛于中小规模旅行商问题的全局最优解,实验表明改进的混合粒子群算法是有效的。     

基于极值动力学的自组织优化算法求解TSP问题

旅行商问题(traveling salesman problem, TSP)具有很强的理论研究和工程应用价值. 在定义离散状态变量和局部适应度的基础上, 分析了TSP优化解的微观特征; 将自组织临界(self-organized criticality, SOC)的概念引入到组合优化领域, 提出了一种基于极值动力学的自组织优化算法. 该算法利用快速下降和间断涨落的动态搜索过程, 高效地遍历解空间中的局部最优解. 针对TSPLIB中典型实例, 计算结果表明其求解效率和优化性能均优于模拟退火和遗传算法等优化方法. 文中算法提供了一种全新的思路, 有助于从系统角度理解组合优化问题的复杂性, 并分析合理的优化动力学过程.     

Diversity-adaptive parallel memetic algorithm for solving large scale combinatorial optimization problems

Parallel memetic algorithms (PMAs) are a class of modern parallel meta-heuristics that combine evolutionary algorithms, local search, parallel and distributed computing technologies for global optimization. Recent studies on PMAs for large-scale complex combinatorial optimization problems have shown that they converge to high quality solutions significantly faster than canonical GAs and MAs. However, the use of local learning for every individual throughout the PMA search can be a very computationally intensive and inefficient process. This paper presents a study on two diversity-adaptive strategies, i.e., (1) diversity-based static adaptive strategy (PMA-SLS) and (2) diversity-based dynamic adaptive strategy (PMA-DLS) for controlling the local search frequency in the PMA search. Empirical study on a class of NP-hard combinatorial optimization problem, particularly large-scale quadratic assignment problems (QAPs) shows that the diversity-adaptive PMA converges to competitive solutions at significantly lower computational cost when compared to the canonical MA and PMA. Furthermore, it is found that the diversity-based dynamic adaptation strategy displays better robustness in terms of solution quality across the class of QAP problems considered. Static adaptation strategy on the other hand requires extra effort in selecting suitable parameters to suit the problems in hand.     

多蚁群分级优化的多目标求解方法*

为提高多目标优化方法的求解性能,在给出了蚁群算法优化函数类问题求解方法的基础上,提出了基于多蚁群分级优化多目标问题的求解方法。构建了子蚁群以自身启发式信息及以其他子群的启发式信息获得准Pareto解以及采用各子群的每一只蚂蚁获得的准Pareto解作支配判断,从而提高Pareto解的多样性;构建了父蚁群以准Pareto解作为空间节点构成TSP类似的组合优化问题,其求解结果以获得多目标优化问题的Pareto解的前沿,从而提高Pareto解的均匀分布性。通过优化实例验证,结果表明,多蚁群分级优化的多目标求解方法     

A machine-learning based memetic algorithm for the multi-objective permutation flowshop scheduling problem

In recent years, the historical data during the search process of evolutionary algorithms has received increasing attention from many researchers, and some hybrid evolutionary algorithms with machine-learning have been proposed. However, the majority of the literature is centered on continuous problems with a single optimization objective. There are still a lot of problems to be handled for multi-objective combinatorial optimization problems. Therefore, this paper proposes a machine-learning based multi-objective memetic algorithm (ML-MOMA) for the discrete permutation flowshop scheduling problem. There are two main features in the proposed ML-MOMA. First, each solution is assigned with an individual archive to store the non-dominated solutions found by it and based on these individual archives a new population update method is presented. Second, an adaptive multi-objective local search is developed, in which the analysis of historical data accumulated during the search process is used to adaptively determine which non-dominated solutions should be selected for local search and how the local search should be applied. Computational results based on benchmark problems show that the cooperation of the above two features can help to achieve a balance between evolutionary global search and local search. In addition, many of the best known Pareto fronts for these benchmark problems in the literature can be improved by the proposed ML-MOMA.     

Discrete Spider Monkey Optimization for Travelling Salesman Problem

Meta-heuristic algorithms inspired by biological species have become very popular in recent years. Collective intelligence of various social insects such as ants, bees, wasps, termites, birds, fish, has been investigated to develop a number of meta-heuristic algorithms in the general domain of swarm intelligence (SI). The developed SI algorithms are found effective in solving different optimization tasks. Travelling Salesman Problem (TSP) is the combinatorial optimization problem where a salesman starting from a home city travels all the other cities and returns to home city in the shortest possible path. TSP is a popular problem due to the fact that the instances of TSP can be applied to solve real-world problems, implication of which turns TSP into a standard test bench for performance evaluation of new algorithms. Spider Monkey Optimization (SMO) is a recent addition to SI algorithms based on the social behaviour of spider monkeys. SMO implicitly adopts grouping and regrouping for the interactions to improve solutions; such multi-population approach is the motivation of this study to develop an effective method for TSP. This paper presents an effective variant of SMO to solve TSP called discrete SMO (DSMO). In DSMO, every spider monkey represents a TSP solution where Swap Sequence (SS) and Swap Operator (SO) based operations are employed, which enables interaction among monkeys in obtaining the optimal TSP solution. The SOs are generated using the experience of a specific spider monkey as well as the experience of other members (local leader, global leader, or a randomly selected spider monkey) of the group. The performance and effectiveness of the proposed method have been verified on a large set of TSP instances and the outcomes are compared to other well-known methods. Experimental results demonstrate the effectiveness of the proposed DSMO for solving TSP.     

Dynamics of local search heuristics for the traveling salesman problem

This paper experimentally investigates the dynamical behavior of a search process in a local heuristic search system for a combinatorial optimization problem. Or-opt heuristic algorithm is chosen as the study subject, and the well-known traveling salesman problem (TSP) serves as a problem testbed. This study constructs the search trajectory by using the time-delay method, evaluates the dynamics of the local search system by estimating the correlation dimension for the search trajectory, and illustrates the transition of the local search process from high-dimensional stochastic to low dimensional chaotic behavior.     

压缩搜索空间法解TSP

旅行商问题(TSP)是一个著名的组合优化问题,从TSP的区域特性入手,提出并详细描述了将搜索剪枝算法与遗传算法相结合的剪枝表法.在对中国旅行商问题(CTSF)的实验中,剪枝表法表现出了良好的寻优能力和鲁棒性,是一种新的可行解决方案.     

An interactive simulation and analysis software for solving TSP using Ant Colony Optimization algorithms

Traveling salesman problem (TSP) is one of the extensively studied combinatorial optimization problems and tries to find the shortest route for salesperson which visits each given city precisely once. Ant colony optimization (ACO) algorithms have been used to solve many optimization problems in various fields of engineering. In this paper, a web-based simulation and analysis software (TSPAntSim) is developed for solving TSP using ACO algorithms with local search heuristics. Algorithms are tested on benchmark problems from TSPLIB and test results are presented. Importance of TSPAntSim providing also interactive visualization with real-time analysis support for researchers studying on optimization and people who have problems in form of TSP is discussed.     

Particle swarm optimization-based algorithms for TSP and generalized TSP

A novel particle swarm optimization (PSO)-based algorithm for the traveling salesman problem (TSP) is presented. An uncertain searching strategy and a crossover eliminated technique are used to accelerate the convergence speed. Compared with the existing algorithms for solving TSP using swarm intelligence, it has been shown that the size of the solved problems could be increased by using the proposed algorithm.Another PSO-based algorithm is proposed and applied to solve the generalized traveling salesman problem by employing the generalized chromosome. Two local search techniques are used to speed up the convergence. Numerical results show the effectiveness of the proposed algorithms.     

A modified ant system to achieve better balance between intensification and diversification for the traveling salesman problem

This paper presents a new variant of Ant Colony Optimization (ACO) for the Traveling Salesman Problem (TSP). ACO has been successfully used in many combinatorial optimization problems. However, ACO has a problem in reaching the global optimal solutions for TSPs, and the algorithmic performance of ACO tends to deteriorate significantly as the problem size increases. In the proposed modification, adaptive tour construction and pheromone updating strategies are embedded into the conventional Ant System (AS), to achieve better balance between intensification and diversification in the search process. The performance of the proposed algorithm is tested on randomly generated data and well-known existing data. The computational results indicate the proposed modification is effective and efficient for the TSP and competitive with Ant Colony System (ACS), Max-Min Ant System (MMAS), and Artificial Bee Colony (ABC) Meta-Heuristic.     

Hybrid algorithms for the twin–screw extrusion configuration problem

The twin-screw configuration problem (TSCP) arises in the context of polymer processing, where twin-screw extruders are used to prepare polymer blends, compounds or composites. The goal of the TSCP is to define the configuration of a screw from a given set of screw elements. The TSCP can be seen as a sequencing problem as the order of the screw elements on the screw axis has to be defined. It is also inherently a multi-objective problem since processing has to optimize various conflicting parameters related to the degree of mixing, shear rate, or mechanical energy input among others. In this article, we develop hybrid algorithms to tackle the bi-objective TSCP. The hybrid algorithms combine different local search procedures, including Pareto local search and two phase local search algorithms, with two different population-based algorithms, namely a multi-objective evolutionary algorithm and a multi-objective ant colony optimization algorithm. The experimental evaluation of these approaches shows that the best hybrid designs, combining Pareto local search with a multi-objective ant colony optimization approach, outperform the best algorithms that have been previously proposed for the TSCP.     

改进的麻雀搜索算法及其求解旅行商问题

旅行商问题(TSP)是经典的NP难问题,对该问题的研究从未停止,也得到了很多的近似求解算法,但每一种算法都各有特色,正因如此,对旅行商问题总有新的算法在提出.麻雀算法是新近提出的算法,本文对麻雀搜索算法(SSA)的原理、搜索策略以及算法的基本流程进行研究分析,针对SSA搜索接近全局最优时,种群的多样性减少,容易陷入局部...     

A great deluge and tabu search hybrid with two-stage memory support for quadratic assignment problem

A two-stage memory architecture is maintained within the framework of great deluge algorithm for the solution of single-objective quadratic assignment problem. Search operators exploiting the accumulated experience in memory are also implemented to direct the search towards more promising regions of the solution space. The level-based acceptance criterion of the great deluge algorithm is applied for each best solution extracted in a particular iteration. The use of short- and long-term memory-based search supported by effective move operators resulted in a powerful combinatorial optimization algorithm. A successful variant of tabu search is employed as the local search method that is only applied over a few randomly selected memory elements when the second stage memory is updated. The success of the presented approach is illustrated using sets of well-known benchmark problems and evaluated in comparison to well-known combinatorial optimization algorithms. Experimental evaluations clearly demonstrate that the presented approach is a competitive and powerful alternative for solving quadratic assignment problems.