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    Spanners for geodesic graphs and visibility graphs

    , Article Algorithmica ; 2017 , Pages 1-15 ; 01784617 (ISSN) Abam, M. A ; Sharif University of Technology
    Springer New York LLC  2017
    Abstract
    Let (Formula presented.) be a set of n points inside a polygonal domain (Formula presented.). A polygonal domain with h holes (or obstacles) consists of h disjoint polygonal obstacles surrounded by a simple polygon which itself acts as an obstacle. We first study t-spanners for the set (Formula presented.) with respect to the geodesic distance function (Formula presented.) where for any two points p and q, (Formula presented.) is equal to the Euclidean length of the shortest path from p to q that avoids the obstacles interiors. For a case where the polygonal domain is a simple polygon (i.e., (Formula presented.)), we construct a ((Formula presented.))-spanner that has (Formula presented.)... 

    Touring convex polygons in polygonal domain fences

    , Article 11th International Conference on Combinatorial Optimization and Applications, COCOA 2017, 16 December 2017 through 18 December 2017 ; Volume 10628 LNCS , 2017 , Pages 61-75 ; 03029743 (ISSN); 9783319711461 (ISBN) Ahadi, A ; Mozafari, A ; Zarei, A ; Sharif University of Technology
    Springer Verlag  2017
    Abstract
    In the touring polygons problem (TPP), for a given sequence (s= P0, P1, ⋯, Pk, t = Pk+1) of polygons in the plane, where s and t are two points, the goal is to find a shortest path that starts from s, visits each of the polygons in order and ends at t. In the constrained version of TPP, there is another sequence (F0, ⋯, Fk) of polygons called fences, and the portion of the path from Pi to Pi+1 must lie inside the fence Fi. TPP is NP-hard for disjoint non-convex polygons, while TPP and constrained TPP are polynomially solvable when the polygons are convex and the fences are simple polygons. In this work, we present the first polynomial time algorithm for solving constrained TPP when the... 

    Spanners for geodesic graphs and visibility graphs

    , Article Algorithmica ; Volume 80, Issue 2 , February , 2018 , Pages 515-529 ; 01784617 (ISSN) Abam, M. A ; Sharif University of Technology
    Springer New York LLC  2018
    Abstract
    Let P be a set of n points inside a polygonal domain D. A polygonal domain with h holes (or obstacles) consists of h disjoint polygonal obstacles surrounded by a simple polygon which itself acts as an obstacle. We first study t-spanners for the set P with respect to the geodesic distance function π where for any two points p and q, π(p, q) is equal to the Euclidean length of the shortest path from p to q that avoids the obstacles interiors. For a case where the polygonal domain is a simple polygon (i.e., h= 0), we construct a (10+ϵ)-spanner that has O(nlog 2n) edges. For a case where there are h holes, our construction gives a (5 + ϵ)-spanner with the size of O(nhlog2n). Moreover, we study... 

    Utilizing distributed learning automata to solve stochastic shortest path problems

    , Article International Journal of Uncertainty, Fuzziness and Knowlege-Based Systems ; Volume 14, Issue 5 , 2006 , Pages 591-615 ; 02184885 (ISSN) Beigy, H ; Meybodi, M. R ; Sharif University of Technology
    2006
    Abstract
    In this paper, we first introduce a network of learning automata, which we call it as distributed learning automata and then propose some iterative algorithms for solving stochastic shortest path problem. These algorithms use distributed learning automata to find a policy that determines a path from a source node to a destination node with minimal expected cost (length). In these algorithms, at each stage distributed learning automata determines which edges to be sampled. This sampling method may result in decreasing unnecessary samples and hence decreasing the running time of algorithms. It is shown that the shortest path is found with a probability as close as to unity by proper choice of... 

    A shortest path problem in an urban transportation network based on driver perceived travel time

    , Article Scientia Iranica ; Volume 17, Issue 4 A , August , 2010 , Pages 285-296 ; 10263098 (ISSN) Ramazani, H ; Shafahi, Y ; Seyedabrishami, S. E ; Sharif University of Technology
    2010
    Abstract
    This paper proposes a method to solve shortest path problems in route choice processes when each link's travel time is a fuzzy number, called the Perceived Travel Time (PTT). The PTT is a subjective travel time perceived by a driver. The algorithm solves the fuzzy shortest path problem (FSPA) for drivers in the presence of uncertainty regarding route travel time. For congested networks, the method is able to find the shortest path in terms of perceived travel time and degree of saturation (congestion) along routes at the same time. The FSPA can be used to support the fuzzification of traffic assignment algorithms. The applicability of the resulting FSPA for the traffic assignment was tested... 

    An iterative stochastic algorithm based on distributed learning automata for finding the stochastic shortest path in stochastic graphs

    , Article Journal of Supercomputing ; Volume 76, Issue 7 , 2020 , Pages 5540-5562 Beigy, H ; Meybodi, M. R ; Sharif University of Technology
    Springer  2020
    Abstract
    In this paper, we study the problem of finding the shortest path in stochastic graphs and propose an iterative algorithm for solving it. This algorithm is based on distributed learning automata (DLA), and its objective is to use a DLA for finding the shortest path from the given source node to the given destination node whose weight is minimal in expected sense. At each stage of this algorithm, DLA specifies edges needed to be sampled. We show that the given algorithm finds the shortest path with minimum expected weight in stochastic graphs with high probability which can be close to unity as much as possible. We compare the given algorithm with some distributed learning automata-based... 

    Solving stochastic path problem: particle swarm optimization approach

    , Article Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics), 18 June 2008 through 20 June 2008, Wroclaw ; Volume 5027 LNAI , 2008 , Pages 590-600 ; 03029743 (ISSN); 354069045X (ISBN); 9783540690450 (ISBN) Momtazi, S ; Kafi, S ; Beigy, H ; Sharif University of Technology
    2008
    Abstract
    An stochastic version of the classical shortest path problem whereby for each node of a graph, a probability distribution over the set of successor nodes must be chosen so as to reach a certain destination node with minimum expected cost. In this paper, we propose a new algorithm based on Particle Swarm Optimization (PSO) for solving Stochastic Shortest Path Problem (SSPP). The comparison of our algorithm with other algorithms indicates that its performance is suitable even by the less number of iterations. © 2008 Springer-Verlag Berlin Heidelberg  

    A Trip-Chain Based Traffic Assignment Model of Electric Vehicles

    , M.Sc. Thesis Sharif University of Technology Tarighati Tabesh, Mahmood (Author) ; Zokaei Aashtiani, Hedayat (Supervisor)
    Abstract
    The goal of this research is to solve the traffic assignment of electric vehicles with considering trip chains. Limited driving range of electric vehicles is considered as one the most important obstacles for the development of these cars. The worry that the battery will run out of power before the destination is an important issue regarding the electric cars and people usually experience it more in trip chains. In this research, a complementary model and a linearization method is used for traffic assignment. In determining shortest paths in the traffic assignment, in addition to considering the travel time and the distance limit, the constraint of passing through activity nodes is... 

    Problem Solving of Gasoline and Electric Vehicles Traffic Assignment with Variable Demand

    , M.Sc. Thesis Sharif University of Technology Davazdah Emami, Behnam (Author) ; Zakaei Aashtiani, Hedayat (Supervisor)
    Abstract
    During the past decade the ever increasing volume of greenhouse gases due to fossil fuels consumption have made humans to seek for alternative, non-polluting fuels as an effective strategy to reduce pollution and prevent environmental issues thereof. Electric cars are today known as one of the most effective solutions for this purpose. Of course, transition from gasoline-powered cars to electric cars in a wide scale is not technically possible in short term due to technological and infrastructural limitations. As a result, this lengthy process would lead to emergence of a combinational transportation system including both gas and electric-powered vehicles. The major differences between these... 

    Developing a Methodology for Evaluating the Vulnerability of Urban Transportation Networks after an Earthquake

    , M.Sc. Thesis Sharif University of Technology Mahmoudabadi, Mahdiyeh (Author) ; Nassiri, Habibollah (Supervisor)
    Abstract
    Natural disasters, earthquakes in particular, claim many human lives and damage major lifelines such as transportation networks. Transportation networks play an important role in various stages of response to disasters, such as evacuation, search, rescue and reconstruction missions. Hence, special attention must be paid to transportation networks in any disaster management system. Hence, in order to reduce the impacts of earthquakes on denser cities and metropolitan areas, analysis of the resiliency and vulnerability of critical infrastructures such as transportation network, can be used as an effective strategy.The resiliency and vulnerability of transportation network have attract a lot... 

    Post-disaster Resilience of Transportation Network using Route Diversity Factor

    , M.Sc. Thesis Sharif University of Technology Karamzadeh Esfahani, Hadi (Author) ; Nasiri, Habibollah (Supervisor)
    Abstract
    Natural hazards such as earthquake take many lives each year and cause significant damages to infrastructures such as transportation networks. Whether after occurrence of a natural disaster like storm in order to evacuate, or after an abrupt event such as earthquake in order to provide emergency measures, a transportation network should maintain its functionality and performance in an acceptable degree and should recover in an effectively short period of time. In this study, the link or the set of links which their removal causes significant damage to the transportation network are identified. A specific index (N-Q index) has been used to describe the performance of the network. In addition,... 

    Sensitivity Analysis and Optimization in Network Flows

    , Ph.D. Dissertation Sharif University of Technology Aini, Asghar (Author) ; Eshghi, Kourosh (Supervisor)
    Abstract
    In today's life, we look at each other, seeing different networks, such as power networks, telecommunication networks, transportation networks (freeways, roads, streets), rail networks, air service networks, shipping networks, Logistics networks (networks of construction and distribution), computer networks, Internet networks (e-commerce, banking networks), airline reservation networks, social networks and so on. In all of these networks, an entity such as man, product, car, electricity, message, information, aircraft, etc. from one source into a destination is moved according to the network's purposes and objectives.This thesis analyzes the sensitivity analysis and optimization of... 

    Weighted TINs Smplification and Design of Some Algorithms on it

    , M.Sc. Thesis Sharif University of Technology Dabaghi Zarandi, Fahimeh (Author) ; Ghodsi, Mohammad (Supervisor)
    Abstract
    Due to increasing quality of satellite images, volume of stored data significantly increased, so speed of statistical and computational processing decreased. For solving this problem, simplification
    problem has been suggested. Surface simplification problem is a fundamental problem in computational geometry and it has many applications in other fields such as GIS, computer graphics, and image processing. Major goal of simplification problems is reducing stored information in any surface, Because it improves speed of processes. One of common types in this field is 3D terrain simplification while error of simplified surface be acceptable. Simplification is NP-Hard problem. In this project,... 

    Multi-objective Route Planning in a Multi-modal Network with Alternative Paths

    , M.Sc. Thesis Sharif University of Technology Tabrizian, Siavash (Author) ; Kourosh, Eshghi (Supervisor)
    Abstract
    In respect of increasing expanse public urban transport, road network complexity as well optimized route planning is necessary in transport network more than ever. Multi-modal network is a transport network which has various means of transportation modes. In that network the presentation a sequence transport mode is essential apart from determining the optimal route. Although choosing the shortest viable path has some limitation the user chooses that. In this paper a modal path planning in multi-modal network has been expressed which two objective functions in addition to minimize the number of change modes have been designed the first is cost and the second is time. Moreover, in this... 

    Analysis and Evaluation of Routing Protocols Conformance Test

    , M.Sc. Thesis Sharif University of Technology Tabatabaee, Hosein (Author) ; Jahangir, Amir Hossein (Supervisor)
    Abstract
    Nowadays, one of the problems of network designers and users is the correctness of network equipment functionality. Since routers play an important role in information transfer between various networks and communicate with each other through a routing protocol, any violation of such protocol can result in the network's failure or defective transfer of data. Thus, being assured of the conformance of the implemented protocol in a router with what has been defined in the protocol's standard is of great significance. To this end, before using or exposing a router, network equipment testers should run protocol conformance tests on it and insure its correct functionality. This brings up the... 

    Analysis and Evaluation of Router Security Based on a Routing Protocol

    , M.Sc. Thesis Sharif University of Technology Tizpaz Niari, Saeed (Author) ; Jahangir, Amir Hossein (Supervisor)
    Abstract
    The importance of routers in information transfer among networks is critical. Thus, vulnerabilities and security deficiencies in routers and the related services like routing protocols can be destructive not only for some hosts, but also for the whole network. Hence, it is necessary that 1) vulnerabilities related to the routers and their services be evaluated and analyzed, and 2) the functional aspects of routers related to the vulnerabilities be formally modeled and analyzed. In this thesis, we present a method for the evaluation and the analysis of OSPF routing protocol from the security point of view. First, reported vulnerabilities on the OSPF are collected and evaluated by a... 

    Analysis and Verification of a Routing Protocol Conformance Test Program

    , M.Sc. Thesis Sharif University of Technology Hosseini Shakib, Seyed Mostafa (Author) ; Jahangir, Amir Hossein (Supervisor)
    Abstract
    Routers play a key role in transferring information between various Networks. It is very important to make sure about the compatibility of OSPF in a router with its standard description. In this regard, before presenting or applying a router and also evaluating its performance, it is necessary to carry out conformance test with the help of network equipment testers Tester designers extract test cases from protocol standard description through non-formal ways and exam them on network equipment.
    In this thesis, a part of OSFP protocol has been modeled through colored Petri nets. In this regard, two sections of OSPF RFC have been model checked: neighbor state machine and data base... 

    Touring polygons: An approximation algorithm

    , Article Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) ; Volume 7643 LNCS , 2012 , Pages 110-121 ; 03029743 (ISSN); 9783642359255 (ISBN) Mozafari, A ; Zarei, A ; Government of India, Department of Science and Technology; Council of Scientific and Industrial Research; Kalasalingam University (KLU) ; Sharif University of Technology
    2012
    Abstract
    In this paper, we introduce a new version of the shortest path problem appeared in many applications. In this problem, there is a start point s, an end point t, an ordered sequence =(S0 = s, S1,...,S k, Sk+1 = t) of sets of polygons, and an ordered sequence =(F0,...,Fk) of simple polygons named fences in such that each fence Fi contains polygons of Si and Si+1. The goal is to find a path of minimum possible length from s to t which orderly touches the sets of polygons of in at least one point supporting the fences constraints. This is the general version of the previously answered Touring Polygons Problem (TPP). We prove that this problem is NP-Hard and propose a precision sensitive FPTAS... 

    Computing a fuzzy shortest path in a network with mixed fuzzy arc lengths using α-cuts

    , Article Computers and Mathematics with Applications ; Volume 60, Issue 4 , 2010 , Pages 989-1002 ; 08981221 (ISSN) Tajdin, A ; Mahdavi, I ; Mahdavi Amiri, N ; Sadeghpour Gildeh, B ; Sharif University of Technology
    2010
    Abstract
    We are concerned with the design of a model and an algorithm for computing a shortest path in a network having various types of fuzzy arc lengths. First, we develop a new technique for the addition of various fuzzy numbers in a path using α-cuts by proposing a linear least squares model to obtain membership functions for the considered additions. Then, using a recently proposed distance function for comparison of fuzzy numbers, we present a dynamic programming method for finding a shortest path in the network. Examples are worked out to illustrate the applicability of the proposed model  

    Secure overlay routing using key pre-distribution: A linear distance optimization approach

    , Article IEEE Transactions on Mobile Computing ; Volume 15, Issue 9 , 2016 , Pages 2333-2344 ; 15361233 (ISSN) Gharib, M ; Yousefi'zadeh, H ; Movaghar, A ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2016
    Abstract
    Key pre-distribution algorithms have recently emerged as efficient alternatives of key management in today's secure communications landscape. Secure routing techniques using key pre-distribution algorithms require special algorithms capable of finding optimal secure overlay paths. To the best of our knowledge, the literature of key pre-distribution systems is still facing a major void in proposing optimal overlay routing algorithms. In the literature work, traditional routing algorithms are typically used twice to find a NETWORK layer path from the source node to the destination and then to find required cryptographic paths. In this paper, we model the problem of secure routing using...