基于DNA-蚁群算法的车辆路径优化问题求解

蚁群算法在解决车辆路径问题(VRP)时存在过早收敛于局部最优解、收敛速度慢等问题,并且由于蚁群算法的参数选择没有严格规定,如果参数选择不当,将影响其寻找最优解的效率。为解决上述问题,将DNA算法中的交叉变异思想应用于基本蚁群算法中,提出一种新的DNA-蚁群算法,将基本蚁群算法中的参数进行DNA交叉变异,有效控制蚁群算法的参数选择,从而得到一组最优参数来求解VRP模型。实验结果表明,DNA-蚁群算法能有效解决车辆路径优化问题,更快寻找到全局最优解或较优解,提高了基本蚁群算法的寻优能力和效率。     

基于正交实验的蚁群算法在车间调度问题中的应用

提出用正交实验的方法来设置蚁群算法在求解车间调度问题的参数。蚁群算法在求解车间调度问题时的性能大部分依赖于参数的设置,各参数的值不同,则蚁群算法的收敛速度和得到的解也不同,使用正交实验的方法来测试各个参数对蚁群算法性能的影响,通过对实验结果的分析可得出参数的最佳组合方案。用经典的JSP的样例对这种组合方案进行了测试,实验结果表明用正交实验法得到的蚁群算法的参数设置方案可以加快算法的收敛速度,使算法能够得到问题的最优解或近似最优解。     

基于差分演化的自适应参数控制蚁群算法

蚁群算法存在对参数的依赖、早熟和停滞等缺点但具有与其他算法容易结合的特点,据此,将差分演化算法应用到蚁群算法的参数选取中,提出一种改进的蚁群算法。将蚁群算法的参数作为差分演化算法解空间的向量元素,在自适应地寻找蚁群算法最优参数组合的同时求解问题的最优解。改进算法对蚁群算法中的参数进行自适应调整,可避免大量盲目的测试,扩大蚁群算法的搜索空间,提高全局搜索能力。在典型的旅行商问题上进行对比实验,结果验证了改进算法的优化性能高于传统的蚁群算法。     

基于均匀设计和混沌理论的蚁群算法参数调整

蚁群算法中参数选择不当会直接影响算法的全局收敛性和求解效率。为此,分析各参数对算法性能的影响,提出确定蚁群算法参数最优组合的两阶段法,在离线调整阶段将蚁群算法基本模型的参数设定问题描述成多因素多水平的均匀设计,然后在在线调整阶段引入混沌扰动以避免搜索过程陷入局部极值。实验结果表明,两阶段法发现最优解的能力明显优于在线调整前的蚁群算法。     

改进的重叠蚁群优化算法

针对蚁群优化算法在进行全局最优解搜索时容易陷入局部最优解和收敛速度缓慢等缺陷,提出了一种有效求解全局最优解搜索问题的重叠蚁群优化算法。该算法通过设置多个重叠的蚁群系统,并对每一个蚁群初始化不同的参数,之后在蚁群之间进行信息素的动态学习,增强了不同蚁群对最优解的开采能力,避免了算法出现早熟现象。仿真实验结果表明,重叠蚁群优化算法在避免陷入局部最优解方面具有良好的效果,是一种提高蚁群算法性能的有效的改进算法。     

网格环境中一种改进的蚁群任务调度算法*

针对在蚁群算法中初始参数设置对算法收敛性能的影响较大,提出了一种新的改进蚁群算法NACA(new ant colony algorithm),针对蚁群算法中的四个关键参数随机编码,得到初始的染色体,从而获得一组较优解;再利用遗传算法的优点对上一步的结果单点顺序交叉、对换变异、选择操作以产生更好的解;然后以这组数据为蚁群算法下一次的工作备选值,并进行最大次数的循环迭代直至停止,即求得参数组合的近似最优解。将它应用于网格系统任务调度中,系统的性能得到了明显的改善。仿真模拟结果表明,所提出的算法具有更短的调度长度和更宽的适应性,当任务已知时,执行时间约缩短了21.7%,且负载变化时对网格中各处理器资源的影响大大减小。     

基于遗传-蚁群融合算法的OSPF路由算法QoS扩展

OSPF路由协议是现代计算机网络应用最为广泛的路由协议之一,为了适应现代网络应用对路由选择的QoS要求,IETF对其进行了扩展,最短路径算法也采用BF算法。但是,这些算法只能计算满足某一条件的路径集合中最短路径,不能满足对带宽、时延和差错率等多项QoS参数都有要求的最优路由选择。采用遗传算法和蚁群算法相结合的融合算法,继承了遗传算法和蚁群算法的优点,在求精解效率上优于遗传算法,在时间效率上优于蚁群算法,能很好地实现多QoS要求的最优路径计算。测试证明融合算法优化性能和时间性能都取得了很好的效果,可以应用于OSPF协议。     

基于免疫记忆的蚁群算法

充分利用前期迭代中解的信息是构造高效蚁群算法实现的关键之一.文中把免疫记忆和克隆选择的思想引入蚁群算法,提出了基于免疫记忆的蚁群算法(IMBACA).算法通过在原有蚁群模型上增加一个免疫记忆库,将记忆库中的解对应为免疫记忆细胞(及其产生的抗体),将问题对应为抗原,并借鉴克隆选择和免疫记忆的思想进行解的构造和信息素更新.算法从解的质量和时间方面与传统蚁群算法进行了比较,实验结果表明,所提出的IMBACA算法可明显提高传统蚁群算法的性能,同时也为解决其他组合优化问题提出了一个新的思路.     

改进遗传蚁群算法求解优化问题的设计与实现

传统的组合优化蚁群算法在求解优化过程中要消耗大量的时间,极易陷入局部最优解和收敛速度过慢等弊端,同时还会产生大量无用的冗余迭代码,运算效率低;因此,提出一种遗传蚁群优化算法;该算法具备了遗传算法快速搜索全局能力的同时也具备了蚁群算法并行性和正反馈机制;利用遗传算法改变选择算子、交叉算子和变异算子操作来确定路径上信息素的分布,将蚁群算法用于特征选择,采用支持向量机分类器分类性能反馈用于评价特征子集解,并通过对改变信息素的迭代、参数选择和增加对信息素局部更新方式指导特征结点重新组合;仿真实验表明,该算法可以有效提高计算精度,加快收敛速度,优化全局最优解的同时增强了系统的鲁棒性和稳定性。     

一种改进的智能蚁群优化算法

为了提高基本蚁群算法（Ant Colony Algorithm）的全局求解能力,对基本蚁群算法进行了改进,提出了一种高效的智能蚁群优化算法。它修改了基本蚁群算法中信息素、挥发因子的更新规则,使得每轮搜索后信息素的增量能更好地反映解的质量,有效地避免陷入局部最优,以加快收敛;另外,采用了一种最近节点选择策略使之适应大规模问题求解,对路径进行优化,提高搜索效率。通过对TSP问题的仿真结果表明,改进后的蚁群算法在求解最优解和收敛性能方面都取得了很好的效果。     

A comparative study of some concurrency control algorithms for cluster-based communication networks

This paper presents a comparative study of some concurrency control algorithms for distributed databases of computer clusters which emphasize high availability and high performance requirements. For this purpose, we have analyzed some concurrency control algorithms which are used in commercial DBMSs, such as the pessimistic locking algorithm as it verifies transaction conflicts early in their execution phase, and the optimistic algorithm which investigates the presence of conflicts after the execution phase. A new algorithm is proposed and implemented by a simulation program. The three algorithms were tested using different configurations. Simulation results showed that the locking algorithm performed better than the optimistic method in presence of conflicts between transactions, while the optimistic algorithm provided better results in the absence of conflicts. Furthermore, in a distributed database with a certain probability of conflicts, the locking algorithm can be used to guarantee strong consistency and an acceptable level of performance. However, if this probability is negligible, the system performance can be improved by using the optimistic algorithm. The proposed algorithm offers improved performance in numerous cases. As a result, it can be used in a distributed database to guarantee a satisfactory level of performance in the presence of conflicts.     

Plastic limit analysis of frames using ant colony systems

In recent years, heuristic algorithms such as simulated annealing, genetic and ant colony algorithms have found many applications in optimization problems. In this paper, ant colony systems (ACSs) are used to optimize the process of finding the collapse load factor of two-dimensional frames. Three variants of ACS algorithms are developed and their relative performances are compared. It is observed that if an ACS is finely tuned and its parameters are carefully adjusted, satisfactory results can be obtained.     

An Adaptive Strategy Integrating Locking with Optimistic Concurrency Control

is paper presents an adaptive strategy called K-locking algorithm for concurrency control in database system.The algorithm integrates an optimistic approach with he K-lock mechanism to control the degree of transaction interference.It is shown that the K-locking strategy is adaptive to the changes in transaction parameters and outperforms both an optimistic approach and a pessimistic approach.     

求解TSP问题的实数编码演化算法

采用实数编码的染色体表示方式,先后自行设计实现了两种演化算法求解TSP问题.其中第二种算法中使用了自适应演化算子,能有效消除路径上的交叉,并能在一定程度上进行合理的段位移,更加符合该染色体表示方式的特点.实验结果表明,用实数编码的染色体表示方式求解TSP是可行的,而且使用自适应演化算法求解可以取得比较好的结果.     

基于ACS优化BP神经网络的交通流量短时预测方法

交通流量预测是智能交通系统中非常重要的研究领域,因为交通流量的复杂性,传统的预测方法不能很好地预测。提出一种基于[t]分布自适应变异优化的布谷鸟算法,通过动态变异控制尺度和设置多个自由度来构造自适应变异算法,可以获得优于高斯变异和柯西变异的整体优化效果。在此基础上,提出改进布谷鸟搜索算法优化神经网络的交通流量预测模型（ACS-BPNN）,通过优化BP神经网络的初始权值和阈值参数,以提高短时交通流量预测精度。仿真结果表明,该方法取得比较好的预测结果。     

基于JPS策略的ACS移动机器人全局路径规划

针对蚁群系统（ACS）算法收敛速度慢、易陷入局部最优、路径转折点数量过多等问题,提出了一种基于跳点搜索（JPS）策略的ACS全局路径规划算法．该算法在迭代前加入一只特殊蚂蚁,利用方向因子引导该蚂蚁始终朝着目标方向前进,并查询是否存在最简路径;在蚂蚁查询下一个节点时,利用JPS算法思想舍去大部分不需要计算的节点．最后,为验证该方法的有效性,使用不同规格的栅格地图进行了仿真实验,仿真结果表明,改进的ACS算法相比于ACS算法,收敛速度加快、收敛时间缩短,且路径更优．最后将算法应用到实际的基于机器人操作系统（ROS）的移动机器人导航实验中,实验结果表明,改进的ACS算法能够有效地解决移动机器人全局路径规划问题,且能明显提升机器人全局路径规划的效率．     

Boosting system performance with optimistic distributed protocols

Optimistic distributed protocols can dramatically improve system performance if the underlying system assumptions are sound and carry a high degree of probability. Optimistic protocols aggressively execute actions based on best-case system assumptions. Using optimistic protocols unquestionably involves tradeoffs, but if a protocol is well designed and the optimistic assumptions hold frequently enough, the gain in performance outweighs the overhead of repairing actions that execute incorrectly. Optimistic distributed protocols can dramatically improve system performance if the underlying system assumptions are sound and carry a high degree of probability     

动态混沌蚁群系统及其在机器人路径规划中的应用

针对蚁群系统（ACS）解决机器人路径规划问题时种群多样性与收敛速度的不足,对蚁群系统引入动态混沌算子,从而平衡种群多样性和收敛速度之间的关系。动态混沌蚁群系统的核心是在传统蚁群系统引入Logistic混沌算子来增加种群多样性,从而提高解的质量。在迭代前期加入混沌算子,以调整路径中的全局信息素值,增加算法的种群多样性,从而避免算法陷入局域优化解;在后期则转为蚁群系统,来确保动态混沌蚁群系统的收敛速度。仿真结果表明,对于机器人路径规划问题,与蚁群系统相比,动态混沌蚁群系统具有更好的种群多样性、更高的解的质量和更快的收敛速度;与精英蚁群系统（EAS）和基于排序的蚂蚁系统（ASrank）相比,动态混沌蚁群系统能够平衡解的质量与收敛速度之间的关系,即使在复杂障碍物的环境下,动态混沌蚁群系统也能较好地找到最优解。动态混沌蚁群系统能够提升移动机器人路径规划中的效率。     

An ant colony system (ACS) for vehicle routing problem with simultaneous delivery and pickup

In this paper we use an ant colony system (ACS) algorithm to solve the vehicle routing problem with simultaneous delivery and pickup (VRPSDP) which is a combinatorial optimization problem. ACS is an algorithmic approach inspired by the foraging behavior of real ants. Artificial ants are used to construct a solution for the problem by using the pheromone information from previously generated solutions. The proposed ACS algorithm uses a construction rule as well as two multi-route local search schemes. The algorithm can also solve the vehicle routing problem with backhaul and mixed load (VRPBM). An extensive numerical experiment is performed on benchmark problem instances available in literature. It is found that ACS gives good results compared to the existing algorithms.     

An intelligent hybrid optimistic/pessimistic concurrency control algorithm for centralized database systems using modified GSA-optimized ART neural model

Concurrency control is the activity of synchronizing operations issued by concurrent executing transactions on a shared database. The aim of this control is to provide an execution that has the same effect as a serial (non-interleaved) one. The optimistic concurrency control technique allows the transactions to execute without synchronization, relying on commit-time validation to ensure serializability. Effectiveness of the optimistic techniques depends on the conflict rate of transactions. Since different systems have various patterns of conflict and the patterns may also change over time, so applying the optimistic scheme to the entire system results in degradation of performance. In this paper, a novel algorithm is proposed that dynamically selects the optimistic or pessimistic approach based on the value of conflict rate. The proposed algorithm uses an adaptive resonance theory–based neural network in making decision for granting a lock or detection of the winner transaction. In addition, the parameters of this neural network are optimized by a modified gravitational search algorithm. On the other hand, in the real operational environments we know the writeset (WS) and readset (RS) only for a fraction of transactions set before execution. So, the proposed algorithm is designed based on optional knowledge about WS and RS of transactions. Experimental results show that the proposed hybrid concurrency control algorithm results in more than 35 % reduction in the number of aborts in high-transaction rates as compared to strict two-phase locking algorithm that is used in many commercial database systems. This improvement is 13 % as compared to pure-pessimistic approach and is more than 31 % as compared to pure-optimistic approach.