Dynamic Network User Equilibrium with State-Dependent Time Lags

This paper recasts the Friesz et al. (1993) measure theoretic model of dynamic network user equibrium as a controlled variational inequality problem involving Riemann integrals. This restatement is done to make the model and its foundations accessible to a wider audience by removing the need to have a background in functional analysis. Our exposition is dependent on previously unavailable necessary conditions for optimal control problems with state-dependent time lags. These necessary conditions, derived in an Appendix, are employed to show that a particular variational inequality control problem has solutions that are dynamic network user equilibria. Our analysis also shows that use of proper flow propagation constraints obviates the need to explicitly employ the arc exit time functions that have complicated numerical implementations of the Friesz et al. (1993) model heretofore. We close by describing the computational implications of numerically determining dynamic user equilibria from formulations based on state-dependent time lags.     

On the Uniqueness of User Equilibrium Flow with Speed Limit

This technical note focuses on the link flow uniqueness of user equilibrium (UE) with speed limits. Under a mild assumption on the monotonicity of link travel time function, the UE link flow solutions are well recognized to be unique. However, the incorporation of speed limits in the network has undermined the strict monotonicity of link travel time functions, thus the UE flows on the links with speed limits may not be unique. This note addresses the uniqueness problem with two major contributions. First, a polyhedron defined on links is provided, and it is proven that the UE link flow is unique if and only if the polyhedron only contains one value. Second, two concise methods are proposed to mathematically check whether the polyhedron is a singleton, which can be easily solved and convenient for practical use.     

Dynamic User Equilibrium Model for Combined Activity-Travel Choices Using Activity-Travel Supernetwork Representation

Integrated urban transportation models have several benefits over sequential models including consistent solutions, quicker convergence, and more realistic representation of behavior. Static models have been integrated using the concept of Supernetworks. However integrated dynamic transport models are less common. In this paper, activity location, time of participation, duration, and route choice decisions are jointly modeled in a single unified dynamic framework referred to as Activity-Travel Networks (ATNs). ATNs is a type of Supernetwork where virtual links representing activity choices are added to augment the travel network to represent additional choice dimensions. Each route in the augmented network represents a set of travel and activity arcs. Therefore, choosing a route is analogous to choosing an activity location, duration, time of participation, and travel route. A cell-based transmission model (CTM) is embedded to capture the traffic flow dynamics. The dynamic user equilibrium (DUE) behavior requires that all used routes (activity-travel sequences) provide equal and greater utility compared to unused routes. An equivalent variational inequality problem is obtained. A solution method based on route-swapping algorithm is tested on a hypothetical network under different demand levels and parameter assumptions.     

基于蚁群算法的动态用户均衡配流

在路网中,为了使用户的出行时间降到最低,提出一个适用于多OD对的路网的动态用户均衡离散模型,并应用蚁群算法求解动态用户均衡问题.通过设计一个算例,利用仿真得出路网中的流量分配数据,并和二次规划Frank-Wolfe算法求解的流量分配数据进行比较,最后得出蚁群算法在求解动态交通用户均衡问题时具有一定的优势.     

Path-Based Dynamic User Equilibrium Model with Applications to Strategic Transportation Planning

Networks and Spatial Economics - This study proposes an analytical capacity constrained dynamic traffic assignment (DTA) model along with an efficient path-based algorithm. The model can be applied...     

Computing Dynamic User Equilibrium on Large-Scale Networks Without Knowing Global Parameters

Networks and Spatial Economics - Dynamic user equilibrium (DUE) is a Nash-like solution concept describing an equilibrium in dynamic traffic systems over a fixed planning period. DUE is a...     

A Comparison of HDG Methods for Stokes Flow

In this paper, we compare hybridizable discontinuous Galerkin (HDG) methods for numerically solving the velocity-pressure-gradient, velocity-pressure-stress, and velocity-pressure-vorticity formulations of Stokes flow. Although they are defined by using different formulations of the Stokes equations, the methods share several common features. First, they use polynomials of degree k for all the components of the approximate solution. Second, they have the same globally coupled variables, namely, the approximate trace of the velocity on the faces and the mean of the pressure on the elements. Third, they give rise to a matrix system of the same size, sparsity structure and similar condition number. As a result, they have the same computational complexity and storage requirement. And fourth, they can provide, by means of an element-by element postprocessing, a new approximation of the velocity which, unlike the original velocity, is divergence-free and H(div)-conforming. We present numerical results showing that each of the approximations provided by these three methods converge with the optimal order of k+1 in L ² for any k≥0. We also display experiments indicating that the postprocessed velocity is a better approximation than the original approximate velocity. It converges with an additional order than the original velocity for the gradient-based HDG, and with the same order for the vorticity-based HDG methods. For the stress-based HDG methods, it seems to converge with an additional order for even polynomial degree approximations. Finally, the numerical results indicate that the method based on the velocity-pressure-gradient formulation provides the best approximations for similar computational complexity.     

Sensitivity Analysis of User Equilibrium Flows Revisited

This paper addresses certain misconceptions regarding what is known and what may be expected when performing sensitivity analyses of network user equilibrium flow patterns. Our presentation relies on a simple observation: any given user equilibrium sensitivity analysis technique should be employed only when the regularity conditions on which it is based are satisfied. Violating regularity, as we show through previously published numerical examples, as well as new examples presented here for the first time, may well lead to incorrect results when the Tobin-Friesz sensitivity analysis method is applied. This is especially so when the most critical regularity assumption of the Tobin-Friesz method, namely that the unperturbed solution must be a nondegenerate extreme point, is violated. We also illustrate how a degenerate unperturbed solution may sometimes be modified to obtain an appropriate nondegenerate solution, thereby allowing the Tobin-Friesz method to be applied.     

基于自动路径驱动的动态控制流恢复算法

动态控制流恢复方法存在路径覆盖不全的问题。为解决该问题,提出一种基于自动路径驱动的控制流恢复算法。在可控的模拟调试环境中动态执行并分析二进制程序,通过修改CPU程序计数器的值,使驱动程序执行在当前输入条件下无法访问的程序路径,从而构建控制流图。基于该算法,设计实现自动路径驱动控制流恢复系统。测试结果表明,该算法能够较全面地发掘程序执行路径,与传统动态执行算法和交互式反汇编器相比,能有效提高恢复控制流图的覆盖率。     

换热器仿真动态数学模型计算方法比较

该文以石油、化工和火电厂常用的换热器为研究对象，对其仿真动态数学模型的算法进行了研究，重点讨论了梯形法、改进的欧拉法、四阶龙格一库塔法和动态因子法的数值解的稳定性、计算速度以及精度，从中选出最优算法。     

动态调度系统中自适应用户界面的设计与实现

该文以炼化企业的动态调度系统为应用背景，以面向动态调度的自适应用户界面的设计与实现为主要研究内容，分析了当前炼化企业动态调度系统用户操作的流程以及界面的需求并建立起相应的数学模型。借鉴自适应用户界面的相关研究成果，设计了自适应用户界面的体系结构以及用户的动态行为过程，针对流程行业的应用特点提出了利用产生式推理和基于上下文的用户意图捕捉的方法，最后给出应用实例。文中所述方法已经成功在企业中得到应用。使用结果表明，该方法能够有效地开发动态调度系统的自适应用户界面，获得满意效果。     

用户界面逆向工程静态方法和动态方法的分析对比

简介当前应用程序用户界面逆向T程的研究现状,对静态和动态两大类方法给予简单的说明和解释。分别用两种方法对简单系统进行界面信息提取实验．并比较提取信息的准确性和完备性。实验结果表明,动态方法更能准确地提取界面的信息。探讨用户界面逆向工程未来研究工作的重点和方向。     

A Cumulative Perceived Value-Based Dynamic User Equilibrium Model Considering the Travelers’ Risk Evaluation on Arrival Time

This paper presents a cumulative perceived value-based dynamic user equilibrium model by applying the prospect theory to formulate the travelers?? risk evaluation on arrival time. The network uncertainty caused by link exit capacity degradation is incorporated into the analysis. The model which considers departure time and route choices simultaneously is expressed by a variational inequality in a discrete time space. Numerical results show that the travelers?? risk preference indeed has big influence on flow distribution. Our study constitutes a deepening of cognition in developing more realistic dynamic traffic assignment technologies.     

几种Krylov迭代法在潮流计算中的对比

在潮流计算时,绝大部分时间都用在求解大规模稀疏线性方程组Ax=b上。众多文献中运用的迭代法并不统一,它们只注重预处理方法的改进。本文就针对几种流行的Krylov迭代法进行详细介绍,总结特性,并利用实验来分析它们总的FLOPS值和收敛效率。最后,通过评估算法的计算效率,得出一种比较适合潮流计算的Krylov迭代法。     

Ranking Approach for the User Story Prioritization Methods

The AHP （analytic hierarchy process） has been applied in many fields and especially to complex engineering problems and applications. AHP is capable of structuring decision problems and finding mathematically determined judgments built on knowledge and experience. This suggests that AHP should prove useful in agile software development, where complex decisions occur routinely. This paper describes a ranking approach to help stakeholders select the best prioritization method for prioritizing the user stories.     

面向可变用户群体的可搜索属性基加密方案

为解决属性基加密方案中用户撤销繁琐、密文更新计算开销大的问题,提出一种面向可变用户群体的可搜索属性基加密方案.利用二叉树管理撤销列表,当需要撤销用户时,可信中心只要将其加入撤销列表,并通知云服务器更新部分密文,提高了用户撤销的效率.考虑到利用二叉树实现用户撤销会导致系统中用户数量存在上限,当某个二叉树叶结点所代表的用户被撤销后,只要更新二叉树中设置的随机值,其他用户就可以重复使用该结点.基于配对计算为用户提供密文搜索功能,并保证被撤销的用户无法搜索密文.安全性分析表明,该方案在随机谕言模型下满足选择明文不可区分安全性.性能分析和实验数据表明,该方案相比于同类方案,计算开销更小.     

足球机器人动态路径规划方法研究

针对机器人足球系统的高度实时性、不确定性,提出了一种基于统计预测的路径规划方法,该方法考虑到障碍物的速度大小和方向的不确定性,用数学统计的方法对障碍物的运动进行建模;机器人在运动过程中,根据得到的环境信息在机器视觉范围内建立预测窗口和避障窗口,在预测窗口内,机器人根据障碍物的信息建立障碍物的预测区域,在避障窗口内,机器人根据自身的位置与障碍物的预测区域,分别调用切线法或滚动窗口法进行路径规划;该方法属于局部路径规划方法,机器人在移动过程中需要不断更新环境信息来进行避障.     

Dynamic Parameterization for Path Following Control

Path following is a basic skill for robots in industrial use. Since the objective of path following is to make a robot follow the reference path, the velocity of the robot or the timing of the motion does not need to be strictly controlled. In this paper, the reference path is defined as a function of the parameter that has dynamics. Using this parameter, we can define the contour error, which is the error that enables us to measure the distance from the reference path to the configuration of the robot. Although the contour error is suitable for use in path following, the dynamics of the parameter contain singular points at which the dynamics cannot be defined. In order to overcome this difficulty, globally defined dynamics are introduced, and two dynamics are integrated with a switching scheme. In this paper, the asymptotic stability of the whole system is proved theoretically. Computer simulation results also show the effectiveness of the method.     

处理动态优化问题中控制变量路径约束的方法

目前国际上对动态优化问题中的状态变量路径约束已有一些研究,但专门处理控制变量路径约束的方法却鲜见报道. 本文首先介绍两种分别基于三角函数变换、约束算子截断来处理控制变量路径约束的方法,然后提出一种基于光滑化的二次罚函数方法. 光滑化罚函数方法不仅能够处理控制变量路径约束,而且还能同时处理关于状态变量的路径约束. 最后使用目前流行的控制变量参数化 (Control variable parameterization, CVP)策略对最终获得的、不再含控制变量路径约束的动态优化问题求解. 实例测试一展现了三种方法各自的特点;实例测试二表明了光滑罚函数方法的有效性和优越性.