165 research outputs found
Efficient Routing for Disaster Scenarios in Uncertain Networks: A Computational Study of Adaptive Algorithms for the Stochastic Canadian Traveler Problem with Multiple Agents and Destinations
The primary objective of this research is to develop adaptive online algorithms for solving the Canadian Traveler Problem (CTP), which is a well-studied problem in the literature that has important applications in disaster scenarios. To this end, we propose two novel approaches, namely Maximum Likely Node (MLN) and Maximum Likely Path (MLP), to address the single-agent single-destination variant of the CTP. Our computational experiments demonstrate that the MLN and MLP algorithms together achieve new best-known solutions for 10,715 instances. In the context of disaster scenarios, the CTP can be extended to the multiple-agent multiple-destination variant, which we refer to as MAD-CTP. We propose two approaches, namely MAD-OMT and MAD-HOP, to solve this variant. We evaluate the performance of these algorithms on Delaunay and Euclidean graphs of varying sizes, ranging from 20 nodes with 49 edges to 500 nodes with 1500 edges. Our results demonstrate that MAD-HOP outperforms MAD-OMT by a considerable margin, achieving a replan time of under 9 seconds for all instances. Furthermore, we extend the existing state-of-the-art algorithm, UCT, which was previously shown by Eyerich et al. (2010) to be effective for solving the single-source single-destination variant of the CTP, to address the MAD-CTP problem. We compare the performance of UCT and MAD-HOP on a range of instances, and our results indicate that MAD-HOP offers better performance than UCT on most instances. In addition, UCT exhibited a very high replan time of around 10 minutes. The inferior results of UCT may be attributed to the number of rollouts used in the experiments but increasing the number of rollouts did not conclusively demonstrate whether UCT could outperform MAD-HOP. This may be due to the benefits obtained from using multiple agents, as MAD-HOP appears to benefit to a greater extent than UCT when information is shared among agents
Efficient Routing for Disaster Scenarios in Uncertain Networks: A Computational Study of Adaptive Algorithms for the Stochastic Canadian Traveler Problem with Multiple Agents and Destinations
The primary objective of this research is to develop adaptive online algorithms for solving the Canadian Traveler Problem (CTP), which is a well-studied problem in the literature that has important applications in disaster scenarios. To this end, we propose two novel approaches, namely Maximum Likely Node (MLN) and Maximum Likely Path (MLP), to address the single-agent single-destination variant of the CTP. Our computational experiments demonstrate that the MLN and MLP algorithms together achieve new best-known solutions for 10,715 instances. In the context of disaster scenarios, the CTP can be extended to the multiple-agent multiple-destination variant, which we refer to as MAD-CTP. We propose two approaches, namely MAD-OMT and MAD-HOP, to solve this variant. We evaluate the performance of these algorithms on Delaunay and Euclidean graphs of varying sizes, ranging from 20 nodes with 49 edges to 500 nodes with 1500 edges. Our results demonstrate that MAD-HOP outperforms MAD-OMT by a considerable margin, achieving a replan time of under 9 seconds for all instances. Furthermore, we extend the existing state-of-the-art algorithm, UCT, which was previously shown by Eyerich et al. (2010) to be effective for solving the single-source single-destination variant of the CTP, to address the MAD-CTP problem. We compare the performance of UCT and MAD-HOP on a range of instances, and our results indicate that MAD-HOP offers better performance than UCT on most instances. In addition, UCT exhibited a very high replan time of around 10 minutes. The inferior results of UCT may be attributed to the number of rollouts used in the experiments but increasing the number of rollouts did not conclusively demonstrate whether UCT could outperform MAD-HOP. This may be due to the benefits obtained from using multiple agents, as MAD-HOP appears to benefit to a greater extent than UCT when information is shared among agents
Solving Canadian Traveller Problem
Tato prĂĄce se zabĂœvĂĄ problĂ©mem kanadskĂ©ho cestujĂcĂho (CTP), kterĂœ se dĂĄ definovat jako problĂ©m hledĂĄnĂ nejkratĆĄĂ cesty ve stochastickĂ©m prostĆedĂ. V reĆĄerĆĄnĂ ÄĂĄsti prĂĄce je zpracovĂĄn pĆehled typĆŻ tohoto problĂ©mu a k nim existujĂcĂch metod ĆeĆĄenĂ. V dalĆĄĂch ÄĂĄstech se prĂĄce zamÄĆuje na stochastickou variantu CTP (SCTP), pro kterou jsou vybranĂ© metody ĆeĆĄenĂ (strategie) probrĂĄny vĂce do hloubky. ZĂĄroveĆ jsou prezentovĂĄny i originĂĄlnĂ strategie pojmenovanĂ© UCTO2 a UCTP. DĂĄle se prĂĄce zabĂœvĂĄ popisem okennĂ aplikace implementovanĂ© v jazyku Java. Ta byla vyvinuta pro ovÄĆenĂ a otestovĂĄnĂ sprĂĄvnĂ© funkce vybranĂœch strategiĂ. Nakonec jsou vyhodnoceny provedenĂ© experimenty, a z nich plynoucĂ srovnĂĄnĂ vybranĂœch strategiĂ.This thesis deals with Canadian traveller problem (CTP), which can be defined as the shortest path problem in a stochastic environment. The overview of different CTP variants is presented in theoretical part of this thesis, as well as known solutions to these variants. In the next parts, the thesis focuses on the stochastic variation of CTP (SCTP). For this variant chosen solutions (strategies) are discussed more in depth. At the same time, the original strategies named UCTO and UCTP are presented. Further, the thesis deals with the description of a window application implemented in Java, which has been developed to validate and test the functionality of selected strategies. The final part contains experiments and comparison of selected strategies.
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Approximation schemes for network, clustering and queueing models
In this dissertation, we consider important optimization problems that arise in three different domains, namely network models, clustering problems and queueing models. To be more specific, we focus on devising efficient traffic routing models, deriving exact convex reformulation to the well-known K-means clustering problem and studying the classical Naorâs observable queues under uncertain parameters. In the following chapters, we discuss these problems in detail, design efficient and tractable solution methodologies, and assess the quality of proposed solutions. In the first part of the dissertation, we analyze a limited-adaptability traffic routing model for the Austin road network. Routing a person through a traffic network presents a tension between selecting a fixed route that is easy to navigate and selecting an aggressively adaptive route that minimizes the expected travel time. We develop non-aggressive adaptive routes in the middle-ground seeking the best of both these extremes. Specifically, these routes still adapt to changing traffic condition, however we limit the total number of allowable adjustments. This improves the user experience, by providing a continuum of options between saving travel time and minimizing navigation. We design strategies to model single and multiple route adjustments, and investigate enumerative techniques to solve these models. We also develop tractable algorithms with easily computable lower and upper bounds to handle real-size traffic data. We finally present the numerical results highlighting the benefit of different levels of adaptability in terms of reducing the expected travel time. In the second part of the dissertation, we study the well-known classical K-means clustering problem. We show that the popular K-means clustering problem can equivalently be reformulated as a conic program of polynomial size. The arising convex optimization problem is NP-hard, but amenable to a tractable semidefinite programming (SDP) relaxation that is tighter than the current SDP relaxation schemes in the literature. In contrast to the existing schemes, our proposed SDP formulation gives rise to solutions that can be leveraged to identify the clusters. We devise a new approximation algorithm for K-means clustering that utilizes the improved formulation and empirically illustrate its superiority over the state-of-the-art solution schemes. Finally, we study an extension of Naorâs analysis [74] on the joining or balking problem in observable M/M/1 queues, relaxing the principal assumption of deterministic arrival and service rates. While all the Markovian assumptions still hold, we assume the arrival and service rates are uncertain and study this problem under stochastic and distributionally robust settings. In the former setting, the exact rates are unknown but we assume the distribution of rates are known to all the decision makers. We derive the optimal joining threshold strategies from the perspective of an individual customer, a social optimizer and a revenue maximizer, such that expected profit rate is maximized. In the distributionally robust setting, we go a step further to assume the true distributions are unknown and the decision makers have access to only a finite set of training samples. Similar to the stochastic setting, we derive optimal thresholds such that the worst-case expected profit rates are maximized. Finally, we compare our observations, both theoretically and numerically, with Naorâs classical results.Operations Research and Industrial Engineerin
Solvency, company directorsâ duties and the problem of process and enforcement - A comparative study
This study examines the legal provisions in relation to creditorsâ protection, particularly when the company is insolvent and seeks to compare different statutory approaches with the view of determining the best reforms for Malaysia. Three jurisdictions have been chosen; the United Kingdom, New Zealand and Australia as the basis of comparison due to similar legal history as these countries have often been referred by the Malaysian Courts to assist in the interpretation of the law. To determine the question of creditorsâ protection, the thesis will address several main issues. Firstly, the thesis examines the relationship between separate legal entity and limited liability. To do so it questions the circumstances when directors will be personally liable for the debt of the company and the extent to which they are liable. The issue will be explored in the light of the shareholder primacy theory which forms the basis of company law. Directorsâ duties therefore are developed with the view of protecting shareholders; and the failure to do so will cause directors to be personally liable. The thesis also considers the arguments for stakeholdersâ theory which mandates directors to take account of other stakeholdersâ interests in addition to shareholdersâ when making decisions. Secondly, it also investigates on how the piercing of the corporate veil and imposing liability on directors will provide protection to creditors especially when the company is insolvent. In order to do so, it scrutinizes the legislative initiatives on the issue as well as the judicial response to the statute. The thesis traces the reforms of the historical doctrine of capital maintenance and the use of solvency test as a replacement to protect creditors. It also provides comprehensive analyses of the law on the issue of remedies in order to ascertain whether the current legal provisions are adequately to protect creditors
Hotel property development : a framework for successful developments
Although there are similarities between hotel and other commercial property developments in terms of land, structures and services, it is important when developing hotels to understand that they have unique characteristics. These unique characteristics are that hotels require specific management expertise, are usually a âsingle-useâ property, whose primary revenue is generated from a service-based industry, and has a market value that is directly related to its ability to generate future net income. The essence of successful hotel property developments lies in understanding these unique characteristics, as illustrated in the dissertation literature review. In addition, the dissertation identifies various critical success factors for hotel development which in turn is incorporated into a hotel property development framework, establishing a practical âroad mapâ for successful hotel developments. The literature review incorporates a wide range of hotel topics, such as the principles of a hotel business, fundamentals of the tourism industry as a motivator for hotel development, property development in general, hotel property development, strategic hotel management, hotel property development feasibility studies, hotel market analysis, financial feasibility, risk management of hotel developments, financing of hotel property developments, the project team and consultants, the design phases, and finally the construction phase. The dissertation empirical study tests the validity of the hotel property development framework, by presenting it to and questioning hotel development professionals in intensive direct interviews.Dissertation (MSc(Real Estate))--University of Pretoria, 2006.Construction Economicsunrestricte
Reading the Entrails
Before the fall of Imperial Rome, priests cast the guts of sacrificial animals on the temple floor, claiming to be able to divine the future from these entrails. By probing the remains of Alberta's past sacrifices (reading the entrails), the author believes we might dimly see an apparition of Alberta's future. This controversial book vividly portrays the history of land and life in Alberta from the Ice Ages to the present. Making no apologies for his criticism of government, regulators, and large corporations, Conrad aims to strike a discussion at all levels by presenting his arguments intensely. For those interested in natural history, the environment, and the future of Alberta's ecological resources, this provocative book is essential reading
Journey of a book: Bartholomew the Englishman and the Properties of Things
De proprietatibus rerum, âOn the properties of thingsâ, has long been referred to by scholars as a medieval encyclopedia, but evidence suggests that it has been many things to many people. The sheer number of extant manuscript copies and printed editions, along with translations, adaptations, and mentions in poems and sermons, testify to its continuous significance for Europeans of all estates and different walks of life, from the thirteenth to the seventeenth centuries. While first compiled soon after the time of St Francis by a humble continental friar to meet the needs of his expanding religious brotherhood, by 1600 English men of letters had claimed Bartholomew as a noble compatriot and national treasure. What was it about the work that propelled it through a progression of medieval cultures and into an exalted position in the world of English letters? This reception history traces evidence for the journey of âPropertiesâ over four centuries of social, political and religious change
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