Modified differential evolution approach for optimization of planar parallel manipulators force capabilities

The global optimization problem is not easy to solve and is still an open challenge for researchers since an analytical optimal solution is difficult to obtain even for relatively simple application problems. Conventional deterministic numerical algorithms tend to stop the search in local minimum nearest to the input starting point, mainly when the optimization problem presents nonlinear, non-convex and non-differential functions, multimodal and nonlinear. Nowadays, the use of evolutionary algorithms (EAs) to solve optimization problems is a common practice due to their competitive performance on complex search spaces. EAs are well known for their ability to deal with nonlinear and complex optimization problems. The primary advantage of EAs over other numerical methods is that they just require the objective function values, while properties such as differentiability and continuity are not necessary. In this context, the differential evolution (DE), a paradigm of the evolutionary computation, has been widely used for solving numerical global optimization problems in continuous search space. DE is a powerful population-based stochastic direct search method. DE simulates natural evolution combined with a mechanism to generate multiple search directions based on the distribution of solutions in the current population. Among DE advantages are its simple structure, ease of use, speed, and robustness, which allows its application on several continuous nonlinear optimization problems. However, the performance of DE greatly depends on its control parameters, such as crossover rate, mutation factor, and population size and it often suffers from being trapped in local optima. Conventionally, users have to determine the parameters for problem at hand empirically. Recently, several adaptive variants of DE have been proposed. In this paper, a modified differential evolution (MDE) approach using generation-varying control parameters (mutation factor and crossover rate) is proposed and evaluated. The proposed MDE presents an efficient strategy to improve the search performance in preventing of premature convergence to local minima. The efficiency and feasibility of the proposed MDE approach is demonstrated on a force optimization problem in Robotics, where the force capabilities of a planar 3-RRR parallel manipulator are evaluated considering actuation limits and different assembly modes. Furthermore, some comparison results of MDE approach with classical DE to the mentioned force optimization problem are presented and discussed.     

混沌映射的多种群量子粒子群优化算法

针对量子粒子群优化算法存在早熟收敛的问题,提出一种基于Logistics混沌映射变异的多种群量子粒子群优化算法（CMQPSO）,采用分段Logistics混沌映射生成初始粒子群,根据适应度值将群体分为顶层和底层种群。顶层出现聚集时才进行高斯扰动,底层种群则按概率通过Logistics混沌变异生成分布更为均匀的粒子,提高种群的多样性,从而较好地平衡了算法的局部和全局搜索能力。对测试函数的计算表明算法较QPSO等其他算法在搜索能力和收敛速度方面有明显改进。分析了算法重要参数停滞阈值[Cσ]和比例系数[S]对搜索性能的影响,给出合理的取值范围。     

一种粒子群和改进自适应差分进化混合算法及在生产调度中的应用

差分进化算法是一类基于种群的启发式全局搜索技术,但传统的差分进化算法存在停滞现象,容易使算法收敛停止。虽然之后出现了各种版本的自适应差分进化算法,但没有考虑到当代个体的适应值是否向着最优个体的适应值逼近,因此本文提出了一种新型的自适应差分进化算法FMDE。考虑到粒子群算法和差分进化算法类似,为了充分发挥两种算法的特点,提出了自适应差分进化和粒子群的混合算法PSO_FMDE;最后采用测试数据集对性能进行分析。实验结果表明,该算法根据进化过程中的搜索进度自适应地确定变异率,使算法易于跳出局部最优解,以提高全局搜索能力。PSO_FMDE算法较单一算法而言,性能更优,更易于靠近全局最优解。     

Improved salp swarm algorithm based on weight factor and adaptive mutation

Salp Swarm Algorithm (SSA) is a novel swarm intelligent algorithm with good performance. However, like other swarm-based algorithms, it has insufficiencies of low convergence precision and slow convergence speed when dealing with high-dimensional complex optimisation problems. In response to this concerning issue, in this paper, we propose an improved SSA named as WASSA. First of all, dynamic weight factor is added to the update formula of population position, aiming to balance global exploration and local exploitation. In addition, in order to avoid premature convergence and evolution stagnation, an adaptive mutation strategy is introduced during the evolution process. Disturbance to the global extremum promotes the population to jump out of local extremum and continue to search for an optimal solution. The experiments conducted on a set of 28 benchmark functions show that the improved algorithm presented in this paper displays obvious superiority in convergence performance, robustness as well as the ability to escape local optimum when compared with SSA.     

求解混合整数非线性规划问题的改进差分进化算法

针对混合整数非线性规划问题的特点,在差分进化算法的变异操作中加入取整运算,提出了一种适合于求解各种混合整数非线性规划问题的改进差分进化算法.同时,采用时变交叉概率因子的方法以提高算法的全局搜索能力和收敛速率.用四个典型测试函数进行了实验研究,实验结果表明,改进的差分进化算法用于求解混合整数非线性规划问题时收敛速度快,精度高,鲁棒性强.     

A genetic algorithm for shortest path routing problem and the sizing of populations

This paper presents a genetic algorithmic approach to the shortest path (SP) routing problem. Variable-length chromosomes (strings) and their genes (parameters) have been used for encoding the problem. The crossover operation exchanges partial chromosomes (partial routes) at positionally independent crossing sites and the mutation operation maintains the genetic diversity of the population. The proposed algorithm can cure all the infeasible chromosomes with a simple repair function. Crossover and mutation together provide a search capability that results in improved quality of solution and enhanced rate of convergence. This paper also develops a population-sizing equation that facilitates a solution with desired quality. It is based on the gambler ruin model; the equation has been further enhanced and generalized. The equation relates the size of the population, quality of solution, cardinality of the alphabet, and other parameters of the proposed algorithm. Computer simulations show that the proposed algorithm exhibits a much better quality of solution (route optimality) and a much higher rate of convergence than other algorithms. The results are relatively independent of problem types for almost all source-destination pairs. Furthermore, simulation studies emphasize the usefulness of the population-sizing equation. The equation scales to larger networks. It is felt that it can be used for determining an adequate population size in the SP routing problem.     

高维多目标多方向协同进化算法

提出一种高维多目标多方向协同进化算法(HMMCA).该算法利用目标空间内的一组方向向量将多目标优化问题分解成多个方向进行寻优,并提出一种混合变异策略以加强算法在每个方向上的收敛能力;同时,该算法采用改进的交互式模糊支配和拥挤度估计因子来维护外部归档集的规模,增强种群的收敛性和分布性.将该算法与目前性能最好的3种多目标进化算法在标准测试函数集上进行对比实验,所得结果表明HMMCA与其他算法相比具有更好的收敛性和分布性.     

基于自适应惯性权重的樽海鞘群算法

针对标准樽海鞘群算法收敛精度低、收敛速度慢的问题,提出一种基于自适应惯性权重的樽海鞘群算法(AIWSSA).首先,在追随者位置更新公式中引入惯性权重因子评价个体之间的影响程度;然后,结合种群成功率与非线性递减函数对惯性权重因子进行自适应调整,使算法的全局和局部搜索能力得到更好地平衡;最后,为防止算法陷入局部最优,引入差分变异思想对非最优个体进行变异.对12个基准测试函数进行求解,实验结果表明:AIWSSA具有较高的收敛精度、收敛速度和鲁棒性; Wilcoxon统计检验结果表明:与标准樽海鞘群算法、改进的樽海鞘群算法、其他群体智能算法相比, AIWSSA表现出较好的性能.通过将其应用于两种带约束的工程设计问题,验证了AIWSSA的有效性.     

Improving the performance of differential evolution algorithm using Cauchy mutation

Differential evolution (DE) is a powerful yet simple evolutionary algorithm for optimization of real-valued, multimodal functions. DE is generally considered as a reliable, accurate and robust optimization technique. However, the algorithm suffers from premature convergence and/or slow convergence rate resulting in poor solution quality and/or larger number of function evaluation resulting in large CPU time for optimizing the computationally expensive objective functions. Therefore, an attempt to speed up DE is considered necessary. This research introduces a modified differential evolution (MDE) that enhances the convergence rate without compromising with the solution quality. The proposed MDE algorithm maintains a failure_counter (FC) to keep a tab on the performance of the algorithm by scanning or monitoring the individuals. Finally, the individuals that fail to show any improvement in the function value for a successive number of generations are subject to Cauchy mutation with the hope of pulling them out of a local attractor which may be the cause of their deteriorating performance. The performance of proposed MDE is investigated on a comprehensive set of 15 standard benchmark problems with varying degrees of complexities and 7 nontraditional problems suggested in the special session of CEC2008. Numerical results and statistical analysis show that the proposed modifications help in locating the global optimal solution in lesser numbers of function evaluation in comparison with basic DE and several other contemporary optimization algorithms.     

A novel hybrid DE–random search approach for unit commitment problem

Differential evolution (DE) is a population-based stochastic search algorithm, whose simple yet powerful and straightforward features make it very attractive for numerical optimization. DE uses a rather greedy and less stochastic approach to problem-solving than other evolutionary algorithms. DE combines simple arithmetic operators with the classical operators of recombination, mutation and selection to evolve from a randomly generated starting population to a final solution. Although global exploration ability of DE algorithm is adequate, its local exploitation ability is feeble and convergence velocity is too low and it suffers from the problem of untime convergence for multimodal objective function, in which search process may be trapped in local optima and it loses its diversity. Also, it suffers from the stagnation problem, where the search process may infrequently stop proceeding toward the global optimum even though the population has not converged to a local optimum or any other point. To improve the exploitation ability and global performance of DE algorithm, a novel and hybrid version of DE algorithm is presented in the proposed research. This research paper presents a hybrid version of DE algorithm combined with random search for the solution of single-area unit commitment problem. The hybrid DE–random search algorithm is tested with IEEE benchmark systems consisting of 4, 10, 20 and 40 generating units. The effectiveness of proposed hybrid algorithm is compared with other well-known evolutionary, heuristics and meta-heuristics search algorithms, and by experimental analysis, it has been found that proposed algorithm yields global results for the solution of unit commitment problem.

     

Multiobjective differential evolution using homeostasis based mutation for application in software cost estimation

The problem in software cost estimation revolves around accuracy. To improve the accuracy, heuristic/meta-heuristic algorithms have been known to yield better results when it is applied in the domain of software cost estimation. For the sake of accuracy in results, we are still modifying these algorithms. Here we have proposed a new meta-heuristic algorithm based on Differential Evolution (DE) by Homeostasis mutation operator. Software development requires high prediction and low Root Mean Squared Error (RMSE) and mean magnitude relative error(MMRE). The problem in software cost estimation relates to accurate prediction and minimization of RMSE and MMRE, which are used to solve multiobjective optimization. Many versions of DE were proposed, however multi-objective versions where the concept of Pareto optimality is used, are most popular. Pareto-Based Differential Evolution (PBDE) is one of them. Although the performance of this algorithm is very good, its convergence rate can be further improved by minimizing the time complexity of nondominated sorting, and by improving the diversity of solutions. This has been implemented by using efficient nondominated algorithm whose time complexity is better than the previous one and a new mutation scheme is implemented in DE which can provide more diversity among solutions. The proposed variant multiplies the Homeostasis value with one more vector, named the Homeostasis mutation vector, in the existing mutation vector to provide more bandwidth for selecting effective mutant solutions. The proposed approach provides more promising solutions to guide the evolution and helps DE escape the situation of stagnation. The performance of the proposed algorithm is evaluated on twelve benchmark test functions (bi-objective and tri-objective) on the Pareto-optimal front. The performance of the proposed algorithm is compared with other state-of-the-art algorithms on five multi-objective evolutionary algorithms (MOEAs). The result verifies that our proposed Homeostasis mutation strategy performs better than other state-of-the-art algorithms. Finally, application of MODE-HBM is applied to solve in terms of Pareto front, representing the trade-off between development RMSE, MMRE, and prediction for COCOMO model.     

Two-Loop Real-Coded Genetic Algorithms with Adaptive Control of Mutation Step Sizes

Genetic algorithms are adaptive methods based on natural evolution that may be used for search and optimization problems. They process a population of search space solutions with three operations: selection, crossover, and mutation. Under their initial formulation, the search space solutions are coded using the binary alphabet, however other coding types have been taken into account for the representation issue, such as real coding. The real-coding approach seems particularly natural when tackling optimization problems of parameters with variables in continuous domains.A problem in the use of genetic algorithms is premature convergence, a premature stagnation of the search caused by the lack of population diversity. The mutation operator is the one responsible for the generation of diversity and therefore may be considered to be an important element in solving this problem. For the case of working under real coding, a solution involves the control, throughout the run, of the strength in which real genes are mutated, i.e., the step size.This paper presents TRAMSS, a Two-loop Real-coded genetic algorithm with Adaptive control of Mutation Step Sizes. It adjusts the step size of a mutation operator applied during the inner loop, for producing efficient local tuning. It also controls the step size of a mutation operator used by a restart operator performed in the outer loop, for reinitializing the population in order to ensure that different promising search zones are focused by the inner loop throughout the run. Experimental results show that the proposal consistently outperforms other mechanisms presented for controlling mutation step sizes, offering two main advantages simultaneously, better reliability and accuracy.     

一种改进的鲸鱼优化算法

针对鲸鱼优化算法（whale optimization algorithm ,WOA）容易陷入局部最优和收敛精度低的问题进行了研究,提出一种改进的鲸鱼优化算法（IWOA）。该算法通过准反向学习方法来初始化种群,提高种群的多样性;然后将线性收敛因子修改为非线性收敛因子,有利于平衡全局搜索和局部开发能力;另外,通过增加自适应权重改进鲸鱼优化算法的局部搜索能力,提高收敛精度;最后,通过随机差分变异策略及时调整鲸鱼优化算法,避免陷入局部最优。实验选取九个基准函数,所有算法均迭代30次,结果表明：改进的鲸鱼优化与原鲸鱼优化算法以及五种改进的鲸鱼优化算法相比,其均值和标准差均优于其他算法,收敛曲线也优于其他大多数算法。说明改进的鲸鱼优化算法收敛精度和算法稳定性最佳,收敛速度较其他大多数改进的鲸鱼优化算法明显加快。     

基于模糊控制的权重决策灰狼优化算法

针对灰狼优化算法后期收敛速度慢,求解精度低等问题,提出一种基于模糊控制的权重决策灰狼优化算法.首先,提出一种新的非线性收敛因子,以提高算法的全局搜索能力及收敛速度;其次,提出一种基于模糊控制的权重决策策略,通过模糊控制器对决策层的个体赋予不同权重进行种群位置更新的决策,增强算法的寻优能力.选取23个标准测试函数对该算法及对比算法进行数值实验,实验结果表明,本文提出的改进的灰狼优化算法在求解精度和算法稳定性等指标优于对比算法.     

一种基于云模型的多目标进化算法

在多目标进化算法的基础上,提出了一种基于云模型的多目标进化算法(CMOEA).算法设计了一种新的变异算子来自适应地调整变异概率,使得算法具有良好的局部搜索能力.算法采用小生境技术,其半径按X条件云发生器非线性动态地调整以便于保持解的多样性,同时动态计算个体的拥挤距离并采用云模型参数来估计个体的拥挤度,逐个删除种群中超出的非劣解以保持解的分布性.将该算法用于多目标0/1背包问题来测试CMOEA的性能,并与目前最流行且有效的多目标进化算法NSGA-II及SPEA2进行了比较.结果表明,CMOEA具有良好的搜索性能,并能很好地维持种群的多样性,快速收敛到Pareto前沿,所获得的Pareto最优解集具有更好的收敛性与分布性.     

精英化岛屿种群引导的差分进化算法

针对差分进化算法常见的早熟收敛、搜索停滞和求解精度低的问题,研究一种精英化岛屿种群的差分进化算法（EIDE）。为了实现全局搜索与局部搜索能力并重,EIDE划分多个岛屿种群,根据迭代时的适应度情况,动态地将岛屿种群分类为精英岛屿和普通岛屿;针对精英岛屿,提出一种控制参数自适应方法,依据岛屿适应度情况,自适应地调整变异概率与交叉概率,同时算法利用增强局部搜索的变异策略,提高收敛速度与精度;针对普通岛屿,使用适合全局搜索的变异与交叉概率及变异策略,维护种群多样性。EIDE提出了一种可控的“移民”与“个体迁移”策略,控制优质基因流动,有效避免早熟收敛与搜索停滞问题。在9个benchmark函数上的测试结果表明,新算法具有较强的全局寻优能力与稳定性,且收敛速度较快。     

An Electromagnetism-like algorithm for cell formation and layout problem

Implementation of cellular manufacturing systems (CMS) is thriving among manufacturing companies due to many advantages that are attained by applying this system. In this study CMS formation and layout problems are considered. An Electromagnetism like (EM-like) algorithm is developed to solve the mentioned problems. In addition the required modifications to make EM-like algorithm applicable in these problems are mentioned. A heuristic approach is developed as a local search method to improve the quality of solution of EM-like. Beside in order to examine its performance, it is compared with two other methods. The performance of EM-like algorithm with proposed heuristic and GA are compared and it is demonstrated that implementing EM-like algorithm in this problem can improve the results significantly in comparison with GA. In addition some statistical tests are conducted to find the best performance of EM-like algorithm and GA due to their parameters. The convergence diagrams are plotted for two problems to compare the convergence process of the algorithms. For small size problems the performances of the algorithms are compared with an exact algorithm (Branch & Bound).     

以优秀个体为导向的多策略差分进化算法

提出一种以优秀个体为导向的多策略差分进化算法。根据适应度值将种群等分为三个子种群,针对不同的种群使用不同的变异策略和控制参数。针对适应度值较差的种群提出了一种新的变异策略,通过引入学习因子和平衡因子,对提高收敛速度、精度和易陷入局部最优状态进行平衡,并对其中个体的控制参数采取自适应的机制,降低种群陷入停滞状态的概率。除此,在每次迭代完成之后,三个种群会重新组成一个新的种群,从而实现了不同种群之间信息的交互。用19个标准测试函数对所提出算法的性能进行了测试,并将其与一些主流差分算法进行比较。实验结果表明,所提出的算法在大部分函数的收敛速度以及精度上有明显的提升。     

融入变异交叉的改进天牛须算法求解TSP及工程应用

为找到最短路径,克服传统算法收敛速度慢、求解精度低等问题,提出一种融入变异交叉的改进天牛群算法(MBSO).首先将个体天牛转换成群体天牛搜索寻优;在群体进化过程中融入变异和交叉,提高全局搜索到更优结果;最后加入天牛须间长度自适应和步长自适应机制的搜索算法,改善算法的探索能力.将改进的算法通过MATLAB对TSPLIB中的数据集进行仿真实验,并用于PON网络规划问题.证明改进的天牛须算法在收敛速度和求解精度两方面较其他算法都有所提升,算法运行时间平均减少0.3 s,实验结果更接近最优解.     

混合自适应引力搜索优化的特征选择方法

特征选择在许多领域具有重要作用,提出一种基于混合自适应引力搜索算法的特征选择方法,在最大化分类精度的同时从数据样本中选出最小特征子集。算法设计两种解更新策略进行组合式搜索,引入群体约简方法,有效地平衡算法的全局搜索和局部收敛能力,同时提出自适应调控参数,减少参数设置对算法性能的影响。在七组真实数据集中的实验结果表明,从分类精度、特征子集大小和运行时间三方面比较,提出的方法优于原始算法和已有相近算法,具有良好的综合性能,是一种有效的特征选择方法。