低代价最短路径树的快速算法

低代价最短路径树是一种广泛使用的多播树.它能够在保证传送时延最小的同时尽量降低带宽消耗.在DDSP(destination-driven shortest path)算法的基础上,通过改进节点的搜索过程,提出了快速低代价最短路径树算法FLSPT(fast loW-coSt shortest path tree).该算法构造的最短路径树与DDSP算法构造的树具有相同的性能,但其时间复杂度低于DDSP算法.随机网络模型的仿真结果表明,FLSPT算法效率更高.     

基于MPH的时延约束Steiner树算法

为了在时延约束务件下进一步优化组播树代价,并降低算法计算复杂度,研究了时延受限的Steiner树问题.分析了MPH(minimum path heuristic)算法的计算复杂度;在此基础上设计了一个时延约束Steiner树算法DCMPH(delay-constrained MPH)用于构造时延约束最小代价组播树.该算法中每个目的结点通过与当前组播树有最小代价的路径加入组播树;若时延不满足要求,则通过合并最小时延SPT(shortest path tree)树进而产生一个满足时延约束的最小代价组播树.仿真实验表明,DCMPH算法生成的组播树在保证时延要求的情况下,与同类算法相比取得了很好的代价性能和较低的计算复杂度.     

时延受限组播路由的最短路径加速算法求解

分析了时延受限的Steiner树问题,总结了在构建组播树过程中的代价和计算复杂度变化规律,并根据实际网络环境,从优化最短路径出发,提出了一种基于优化最短路径的时延受限组播路由算法AOSPMPH。该算法以MPH算法为基础,利用Floyd最短路径优化算法求出节点对之间的最短路径,选择满足时延要求的最小代价路径加入组播树,进而产生一棵满足时延约束的最小代价组播树。仿真结果表明,AOSPMPH不但能正确地构造时延约束组播树,而且其代价和计算复杂度与其他同类算法相比得到了优化。     

基于增量最短路径优先算法的高效LFA实现方法

针对已有LFA实现方式计算开销大和部署难度高的问题,提出了一种基于增量最短路径优先算法的LFA实现方法（LFA implementation method based on incremental shortest path first algorithm,ERPISPF）。首先将快速实现LFA的问题转换为如何在以计算节点为根的最短路径树上高效地计算其所有邻居节点到网络其余所有节点的最小代价问题;然后提出了计算该代价的定理并且证明了它的正确性,最后从理论上分析了算法的时间复杂度。仿真结果表明,ERPISPF不仅计算开销小,并且与LFC的故障保护率是相同的。     

基于最短路径搜索序列编码的多下一跳路由

多下一跳路由较之单下一跳路由有许多天然的优势,通过分析现有多下一跳路由实现机制下的路由算法,提出了基于最短路径搜索序列编码的多下一跳路由.针对SPT(shortest path tree)路由实现机制无法利用等距离邻居节点之间链路的问题,提出了采用Dijkstra算法对网络节点编码赋值的思想.该方法可以对节点进行严格有序的赋值,规范了链路传输方向,有效地避免了环路,提高了网络资源利用率.仿真分析结果表明了该算法的可行性和有效性.     

低代价最短路径树快速算法的时间复杂度研究

低代价最短路径树是一种广泛使用的多播树,它能够在保证传送时延最小的同时尽量降低带宽消耗.快速低代价最短路径树算法FLSPT是在DDSP算法的基础上,通过改进节点的搜索过程,该算法构造的最短路径树与DDSP算法构造的树具有相同的性能,但其时间复杂度低于DDSP,其时间复杂度为O(nlog n e).FLSPT是利用Fibonacci堆来选择图中未计算点的最小值来计算时间复杂度的.通过对FLSPT的程序和Fibonacci堆的分析发现,用O(log(n!) e)来表示FLSPT算法的时间复杂度比文献[6]中分析的O(nlog(n) e)更能体现FLSPT算法高效率.     

基于共享边的时延约束组播路由算法

为了优化在时延约束下的组播树代价,降低算法计算复杂度,研究了时延受限的Steiner树问题.分析了最短路径启发式(MPH)算法的执行过程,以此为基础提出一个基于共享边的时延约束组播路由算法ESAMPH.该算法在构建组播路由树时能够优先采用包含有较多的最短路径经过的节点,这样后面的组播成员节点到树上的最短路径也有可能经过这些节点,由此实现边的共享,降低了组播树的代价.仿真结果表明,ESAMPH算法在代价、延迟和计算时间之间能获得较好的平衡,综合性能较好.     

一种高效的最短路径完全动态更新算法

在通信网络中,节点间最短路径的计算是链路状态路由协议计算路由的基础。通过对现有动态最短路径算法的深入研究,提出了一种处理网络拓扑变化的完全动态最短路径算法DSPT-ID。该算法利用已有SPT的信息,建立一个最短路径树的更新队列,当网络拓扑发生变化时,算法针对边的权值增大和减小,分别进行更新,并将更新节点局限在受拓扑变化影响的节点中,从而达到SPT的增量更新。算法复杂度分析和仿真结果显示,DSPT-ID算法具有更少的节点更新次数和更高的时间效率。     

基于能量优化的Ad hoc认知无线电网络组播路由启发式算法研究*

提出了两个Ad hoc认知无线电网络中基于能量优化的组播路由启发式算法。一个是基于经典的最短路径树的组播算法（shortest path tree algorithm,SPTA）,另一个是基于能量函数的组播启发式算法(energy function based heuristic algorithm,EFHA)。这两个算法都在考虑了认知无线电网络特性的基础上建立能量优化的组播树,从应用例子可以看出, EFHA算法明显优于SPTA算法,并且复杂度较低。     

Sink轨迹固定传感器网络的高效数据采集机制

在sink移动轨迹固定的传感器网络中,由于sink点有限的通信时间和节点的随机分布,使得很难兼顾数据采集量的提高和整体能耗的降低.为了解决该问题,提出了一种最大数据量最短路径(maximum amount shortest path,简称MASP)数据采集方法.MASP对网络中成员节点与sub-sink节点之间的匹配关系进行集中式优化.采用0-1线性规划方法对MASP问题进行形式化描述,提出了一种基于二维染色体编码的遗传算法进行求解,并给出了相应的数据通信协议设计.另外,MASP可以扩展支持低密度网络和多sink点网络.基于OMNET++的仿真结果表明,MASP在能耗利用率方面要远远优于最短路径树方法(shortest path tree,简称SPT)及固定sink数据采集方法.     

Path Clearance

In military scenarios, agents (i.e., troops of soldiers, convoys, and unmanned vehicles) may often have to traverse environments with only a limited intelligence about the locations of adversaries. We study a particular instance of this problem that we refer to as path clearance problem. In path clearance, an agent has to navigate to its goal as quickly as possible without being detected by an adversary. When picking a path to follow, the agent does not know the precise locations of adversaries. Instead, it has a list of their possible locations, each associated with the probability of containing an adversary. Any of these locations can be sensed by either the agent itself at a distance close enough (provided the agent has a capability of long-range sensing) or by one of the scouts (if they are available). If no adversary is present at a sensed location, the agent can then safely traverse through it. Otherwise, the agent has to take a detour.     

Path Sensitization

For different delay models,the concept of sensitization can be very different.Traditonal concepts of sensitization cannot precisely describe circuit behavior when the input vectors change very fast.Using Boolean process aporoach,this paper presents a new definition of sensitization for arbitrary input waveforms.By this new concept it is found that if the inputs of a combinational circuit can change at any time,and each gate‘s delay varies within an interval (bounded gate delay model),then every path,which is not necessarily a single topological path,is sensitizable.From the experimental results it can be seen that,all nonsensitizable paths for traditional concepts actually can propagate transitions along them for some input waveforms.However,specified time between input transitions(STBIT) and minimum permissible pulse width(ε）are two major factors to make some paths non-sensitizable.     

基于路径索引与编码模式的路径连接

在各种XML查询语言中普遍采用路径表达式来表示对象间的嵌套和引用关系，路径表达式的求解是查询处理中的一个关键问题．本文提出一种基于路径索引与编码模式的路径连接方法，利用路径索引能够以与路径长度成比例的时间求出对象的后代或祖先的目标集，利用编码模式则可以用常数时间确定对象之间的祖先一后代关系．实验结果表明，本文提出的方法具有较高的效率，当对大量对象进行连接以及当路径的长度、路径上结点的出度或入度较大时，本文提出的方法明显优干自顶向下或自底向上遍历的方法。     

Path Summaries and Path Partitioning in Modern XML Databases

XML path summaries are compact structures representing all the simple parent-child paths of an XML document. Such paths have also been used in many works as a basis for partitioning the document’s content in a persistent store, under the form of path indices or path tables. We revisit the notions of path summaries and path-driven storage model in the context of current-day XML databases. This context is characterized by complex queries, typically expressed in an XQuery subset, and by the presence of efficient encoding techniques such as structural node identifiers. We review a path summary’s many uses for query optimization, and given them a common basis, namely relevant paths. We discuss summary-based tree pattern minimization and present some efficient summary-based minimization heuristics. We consider relevant path computation and provide a time- and memory-efficient computation algorithm. We combine the principle of path partitioning with the presence of structural identifiers in a simple path-partitioned storage model, which allows for selective data access and efficient query plans. This model improves the efficiency of twig query processing up to two orders of magnitude over the similar tag-partitioned indexing model. We have implemented the path-partitioned storage model and path summaries in the XQueC compressed database prototype [8]. We present an experimental evaluation of a path summary’s practical feasibility and of tree pattern matching in a path-partitioned store.     

K-Order Surrounding Roadmaps Path Planner for Robot Path Planning

Probabilistic roadmaps are commonly used in robot path planning. Most sampling-based path planners often produce poor-quality roadmaps as they focus on improving the speed of constructing roadmaps without paying much attention to the quality. Poor-quality roadmaps can cause problems such as poor-quality paths, time-consuming path searching and failures in the searching. This paper presents a K-order surrounding roadmap (KSR) path planner which constructs a roadmap in an incremental manner. The planner creates a tree while answering a query, selects the part of the tree according to quality measures and adds the part to an existing roadmap which is obtained in the same way when answering the previous queries. The KSR path planner is able to construct high-quality roadmaps in terms of good coverage, high connectivity, provision of alternative paths and small size. Comparison between the KSR path planner and Reconfigurable Random Forest (RRF), an existing incremental path planner, as well as traditional probabilistic roadmap (PRM) path planner shows that the roadmaps constructed using the KSR path planner have higher quality that those that are built by the other planners.     

路径测试中基本路径集的自动生成

路径测试是一种重要的白盒测试技术,具有较高的故障覆盖率。基本路径集覆盖了程序中所有语句和分支,该文测试了基本路径集中的路径,在测试资源有限的情况下得到较好的测试效果,并提出了基于图的深度优先搜索的基本路径集的生成方法,该算法采用的生成子路径的方法可以有效地减少路径生成过程中的搜索过程,提高路径生成的效率。 关键词：     

Path Coordinates in a 3D Path Following Problem

Two approaches to 3D path coordinates used when solving a path following problem for aerial vehicles are proposed. The first approach lies in reducing the problem to a two-dimensional case by projection. The second approach is based on introducing an adaptive frame at the target point. The choice of the adaptive frame determines the complexity of the algorithm of the control synthesis. It is shown that the parallel transport frame, or the Bishop frame, is most convenient.     

路径表达式的构造方法及路径测试

软件测试是软件设计中一个重要阶段,也是保证软件可靠性的重要手段。路径测试是软件测试中一种重要方法,而测试的关键是确定路径数目和设计测试用例。程序路径表达式是路径测试中路径的一种表示方法。本文讨论了利用程序图进行路径测试中的路径表达式的构造方法。     

基于最优路径存储的游戏寻径算法

研究了应用于游戏中的多个路径搜寻算法, 以及游戏路径搜寻的一些特点, 提出了基于最优路径存储的寻径算法. 主要是通过最优路径矩阵存储部分的最优路径, 减少大量路径的重复计算, 提高游戏中的路径计算效率. 针对游戏场景角色的移动引起路径点通行状态的变化导致当前的最优路径失效, 提出了路径更新算法, 更新最优路径矩阵当中的最优路径. 另外, 针对地图路径点规模增大的情况, 提出了地图路径点分块处理的策略, 然后对每一子块分别使用最优路径矩阵进行路径存储.