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1
Rees, Leigh H. "Chirality : in search of organometallic second order non-linear optic materials." Thesis, University of Bristol, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265324.
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Hepburn, Ian David. "Development of linear InSb array instrumentation and the search for brown dwarfs." Thesis, Imperial College London, 1991. http://hdl.handle.net/10044/1/46816.
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Bothwell, Brian P. "An Iterative Linear Programming Approach to Solving Large Cumulative Search-Evasion Games." Thesis, Monterey, California. Naval Postgraduate School, 1990. http://hdl.handle.net/10945/30678.
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Approved for public release, distribution is unlimitedCumulative search-evasion games (CSEGs) involve two players, a searcher and an evader, who move among some finite set of cells. Neither player is aware of the other player's position during any stage of the game. When the payoff for the game is assumed to be the number of times the searcher and evader occupy the same cell, Eagle and Washburn proposed two solution techniques: one by fictitious play and the other by solving equivalent linear programming formulations. However, both have proved to be time consuming even for moderately sized problems. This thesis considers two alternate linear programming formulations for CSEGs. Since both contain a large number of variables and constraints, the linear programming problems are initially solved with many of the constraints removed. If the solution to this relaxed problem is not a feasible optimal solution, additional constraints are added and the problem is solved again. This process continues until a feasible optimal solution is found. The results from a numerical experimentation with various solution techniques are also presented.
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Madabushi, Ananth R. "Lagrangian Relaxation / Dual Approaches For Solving Large-Scale Linear Programming Problems." Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/36833.
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This research effort focuses on large-scale linear programming problems that arise in the context of solving various problems such as discrete linear or polynomial, and continuous nonlinear, nonconvex programming problems, using linearization and branch-and-cut algorithms for the discrete case, and using polyhedral outer-approximation methods for the continuous case. These problems arise in various applications in production planning, location-allocation, game theory, economics, and many engineering and systems design problems. During the solution process of discrete or continuous nonconvex problems using polyhedral approaches, one has to contend with repeatedly solving large-scale linear programming(LP) relaxations. Thus, it becomes imperative to employ an efficient method in solving these problems. It has been amply demonstrated that solving LP relaxations using a simplex-based algorithm, or even an interior-point type of procedure, can be inadequately slow ( especially in the presence of complicating constraints, dense coefficient matrices, and ill-conditioning ) in comparison with a Lagrangian Relaxation approach. With this motivation, we present a practical primal-dual subgradient algorithm that incorporates a dual ascent, a primal recovery, and a penalty function approach to recover a near optimal and feasible pair of primal and dual solutions.
The proposed primal-dual approach is comprised of three stages. Stage I deals with solving the Lagrangian dual problem by using various subgradient deflection strategies such as the Modified Gradient Technique (MGT), the Average Direction Strategy (ADS), and a new direction strategy called the Modified Average Direction Strategy (M-ADS). In the latter, the deflection parameter is determined based on the process of projecting the unknown optimal direction onto the space spanned by the current subgradient direction and the previous direction. This projected direction approximates the desired optimal direction as closely as possible using the conjugate subgradient concept. The step-length rules implemented in this regard are the Quadratic Fit Line Search Method and a new line search method called the Directional Derivative Line Search Method in which we start with a prescribed step-length and then ascertain whether to increase or decrease the step-length value based on the right-hand and left-hand derivative information available at each iteration. In the second stage of the algorithm (Stage II), a sequence of updated primal solutions is generated using some convex combinations of the Lagrangian subproblem solutions. Alternatively, a starting primal optimal solution can be obtained using the complementary slackness conditions. Depending on the extent of feasibility and optimality attained, Stage III applies a penalty function method to improve the obtained primal solution toward a near feasible and optimal solution.
We present computational experience using a set of randomly generated, structured, linear programming problems of the type that might typically arise in the context of discrete optimization.Master of Science
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Kim, Seongsu. "A BAYESIAN EVIDENCE DEFINING SEARCH." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1429789001.
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Law, Glenn W. (Glenn Woodrow). "Measurements of ocular counterrolling during linear accelerations using an electromagnetic scleral search coil system." Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/43236.
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Stokes, Klara. "Combinatorial structures for anonymous database search." Doctoral thesis, Universitat Rovira i Virgili, 2011. http://hdl.handle.net/10803/52799.
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This thesis treats a protocol for anonymous database search (or if one prefer, a protocol for user-private information retrieval), that is based on the use of combinatorial configurations. The protocol is called P2P UPIR. It is proved that the (v,k,1)-balanced incomplete block designs (BIBD) and in particular the finite projective planes are optimal configurations for this protocol. The notion of n-anonymity is applied to the configurations for P2P UPIR protocol and the transversal designs are proved to be n-anonymous configurations for P2P UPIR, with respect to the neighborhood points of the points of the configuration. It is proved that to the configurable tuples one can associate a numerical semigroup. This theorem implies results on existence of combinatorial configurations. The proofs are constructive and can be used as algorithms for finding combinatorial configurations. It is also proved that to the triangle-free configurable tuples one can associate a numerical semigroup. This implies results on existence of triangle-free combinatorial configurations.
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Vasireddy, Jhansi Lakshmi. "Applications of Linear Algebra to Information Retrieval." Digital Archive @ GSU, 2009. http://digitalarchive.gsu.edu/math_theses/71.
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Some of the theory of nonnegative matrices is first presented. The Perron-Frobenius theorem is highlighted. Some of the important linear algebraic methods of information retrieval are surveyed. Latent Semantic Indexing (LSI), which uses the singular value de-composition is discussed. The Hyper-Text Induced Topic Search (HITS) algorithm is next considered; here the power method for finding dominant eigenvectors is employed. Through the use of a theorem by Sinkohrn and Knopp, a modified HITS method is developed. Lastly, the PageRank algorithm is discussed. Numerical examples and MATLAB programs are also provided.
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Lopez, Soto Claudia Orquidea. "Formulation space search for two-dimensional packing problems." Thesis, Brunel University, 2013. http://bura.brunel.ac.uk/handle/2438/7455.
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The two-dimension packing problem is concerned with the arrangement of items without overlaps inside a container. In particular we have considered the case when the items are circular objects, some of the general examples that can be found in the industry are related with packing, storing and transportation of circular objects. Although there are several approaches we want to investigate the use of formulation space search. Formulation space search is a fairly recent method that provides an easy way to escape from local optima for non-linear problems allowing to achieve better results. Despite the fact that it has been implemented to solve the packing problem with identical circles, we present an improved implementation of the formulation space search that gives better results for the case of identical and non-identical circles, also considering that they are packed inside different shaped containers, for which we provide the needed modifications for an appropriate implementation. The containers considered are: the unit circle, the unit square, two rectangles with different dimension (length 5, width 1 and length 10 width 1), a right-isosceles triangle, a semicircle and a right-circular quadrant. Results from the tests conducted shown several improvements over the best previously known for the case of identical circles inside three different containers: a right-isosceles triangle, a semicircle and a circular quadrant. In order to extend the scope of the formulation space search approach we used it to solve mixed-integer non-linear problems, in particular those with zero-one variables. Our findings suggest that our implementation provides a competitive way to solve these kind of problems.
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Lazic, Jasmina. "New variants of variable neighbourhood search for 0-1 mixed integer programming and clustering." Thesis, Brunel University, 2010. http://bura.brunel.ac.uk/handle/2438/4602.
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Many real-world optimisation problems are discrete in nature. Although recent rapid developments in computer technologies are steadily increasing the speed of computations, the size of an instance of a hard discrete optimisation problem solvable in prescribed time does not increase linearly with the computer speed. This calls for the development of new solution methodologies for solving larger instances in shorter time. Furthermore, large instances of discrete optimisation problems are normally impossible to solve to optimality within a reasonable computational time/space and can only be tackled with a heuristic approach. In this thesis the development of so called matheuristics, the heuristics which are based on the mathematical formulation of the problem, is studied and employed within the variable neighbourhood search framework. Some new variants of the variable neighbourhood searchmetaheuristic itself are suggested, which naturally emerge from exploiting the information from the mathematical programming formulation of the problem. However, those variants may also be applied to problems described by the combinatorial formulation. A unifying perspective on modern advances in local search-based metaheuristics, a so called hyper-reactive approach, is also proposed. Two NP-hard discrete optimisation problems are considered: 0-1 mixed integer programming and clustering with application to colour image quantisation. Several new heuristics for 0-1 mixed integer programming problem are developed, based on the principle of variable neighbourhood search. One set of proposed heuristics consists of improvement heuristics, which attempt to find high-quality near-optimal solutions starting from a given feasible solution. Another set consists of constructive heuristics, which attempt to find initial feasible solutions for 0-1 mixed integer programs. Finally, some variable neighbourhood search based clustering techniques are applied for solving the colour image quantisation problem. All new methods presented are compared to other algorithms recommended in literature and a comprehensive performance analysis is provided. Computational results show that the methods proposed either outperform the existing state-of-the-art methods for the problems observed, or provide comparable results. The theory and algorithms presented in this thesis indicate that hybridisation of the CPLEX MIP solver and the VNS metaheuristic can be very effective for solving large instances of the 0-1 mixed integer programming problem. More generally, the results presented in this thesis suggest that hybridisation of exact (commercial) integer programming solvers and some metaheuristic methods is of high interest and such combinations deserve further practical and theoretical investigation. Results also show that VNS can be successfully applied to solving a colour image quantisation problem.
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Dimelow, David J. "Non-linear dynamics of an offshore mooring tower." Thesis, University of Aberdeen, 1997. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU092912.
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Offshore mooring towers are one of a number of single-point mooring (SPM) systems which provide a berthing point for tankers, enabling the transfer of crude oil to or from the moored vessel. The periodic slackening of the mooring hawser between the vessel and the tower gives rise to a discontinuously non-linear restoring function. Hence, the wave-induced motions of the tower can be highly complex, with the possibility of large amplitude, and potentially hazardous motions. A large amount of work has been carried out in studying single-point mooring systems. However, much of this work has focused on mooring forces and tanker motions. Few studies have looked in-depth at the motions of the mooring structure itself. In this thesis, mooring tower motions have been studied in detail using three techniques: numerical analysis, approximate analytical methods, and experimental modelling. Each of these approaches to the problem has demonstrated that large amplitude and hence potentially hazardous motions can occur. Numerical predictions of motion showed very good comparison with measured responses, particularly for synchronous motions. However, for more complex motions, such as subharmonic resonances, the agreement between measured and predicted results was seen to deteriorate. Approximate analytical methods did not perform so well. Useful results were obtained for the simplified single-degree-of-freedom symmetric model only, highlighting the need for a more sophisticated method. This research has been successful in providing insight into the complex non-linear motions of an offshore mooring tower. The fundamental mechanisms and features of the system have been presented. The methodology used in this study has been applied to the specific case of an offshore mooring tower. However, the general approach to investigating the non-linear motions of the structure is widely applicable in the field of offshore engineering.
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Kevorkiants, Rouslan. "Linear scaling conjugate gradient density matrix search: implementation, validation, and application with semiempirical molecular orbital methods." [S.l. : s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=968547028.
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Rossmanith, Gregor. "Concepts of non-linear data analysis applied to the search of non-Gaussianities in the CMB." Diss., lmu, 2011. http://nbn-resolving.de/urn:nbn:de:bvb:19-138198.
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TORTI, FRANCESCA. "Advances in the forward search: methodological and applied contributions." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2010. http://hdl.handle.net/10281/7791.
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The thesis is about the Forward Search, an approach to robust data analysis proposed and developed in the last 15 years mainly by Atkinson, Riani and Cerioli.
It is a general method for detecting unidentified subsets and masked outliers in complex data and for determining their effect on models fitted to the data.
This thesis approaches the Forward Search in the regression context under different perspectives, motivated by issues encountered in concrete application contexts related to the analysis of international trade data.
The main contributions of the thesis can be summarised as follows.
Firstly, it is investigated how the Forward Search achieves its nominal size and how it faces with the multiple testing issue.
Secondly, the Forward Search algorithm is relaxed in order to identify outliers with arbitrary significance levels, other than the standard 1% that is inherent to the method.
Thirdly, it reports the results of a rigorous and extensive assessment of the actual size and power of the Forward Search in comparison with the today reference methods in robust regression (LMS and LTS). The results empirically prove that the Forward Search can achieve at the same time high power and small size.
Fourthly, the Forward Search is extended to identify and validate homogeneous sub-populations in the data that, in regression, manifest as mixtures of linear components.
Finally the Forward Search is addressed from the exploratory data analysis perspective, discussing new dynamic and interactive graphical tools aimed at extracting information from the numerous plots produced by the Forward Search.
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Sands, William Alvah. "Phylogenetic Inference Using a Discrete-Integer Linear Programming Model." University of Akron / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1492783280743802.
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Gardenghi, John Lenon Cardoso. "Um método de pontos interiores primal-dual viável para minimização com restrições lineares de grande porte." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/45/45134/tde-11072014-084756/.
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Neste trabalho, propomos um método de pontos interiores para minimização com restrições lineares de grande porte. Este método explora a linearidade das restrições, partindo de um ponto viável e preservando a viabilidade dos iterandos. Apresentamos os principais resultados de convergência global, além de uma descrição rica em detalhes de uma implementação prática de todos os passos do método. Para atestar a implementação do método, exibimos uma ampla experimentação numérica, e uma análise comparativa com métodos bem difundidos na comunidade de otimização contínua.In this work, we propose an interior-point method for large-scale linearly constrained optimization. This method explores the linearity of the constraints, starting from a feasible point and preserving the feasibility of the iterates. We present the main global convergence results, together with a rich description of the implementation details of all the steps of the method. To validate the implementation of the method, we present a wide set of numerical experiments and a comparative analysis with well known softwares of the continuous optimization community.
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Chhabra, Meenal. "Studies in the Algorithmic Pricing of Information Goods and Services." Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/25874.
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This thesis makes a contribution to the algorithmic pricing literature by proposing and analyzing techniques for automatically pricing digital and information goods in order to maximize profit in different settings. We also consider the effect on social welfare when agents use these pricing algorithms. The digital goods considered in this thesis are electronic commodities that have zero marginal cost and unlimited supply e.g., iTunes apps. On the other hand, an information good is an entity that bridges the knowledge gap about a product between the consumer and the seller when the consumer cannot assess the utility of owning that product accurately e.g., Carfax provides vehicle history and can be used by a potential buyer of a vehicle to get information about the vehicle.
With the emergence of e-commerce, the customers are increasingly price sensitive and search for the best opportunies anywhere. It is almost impossible to manually adjust the prices with rapidly changing demand and competition. Moreover, online shopping platforms also enable sellers to change prices easily and quickly as opposed to updating price labels in brick and mortar stores so they can also experiment with different prices to maximize their revenue. Therefore, e-marketplaces have created a need for designing sophisticated practical algorithms for pricing. This need has evoked interest in algorithmic pricing in the computer science, economics, and operations research communities.
In this thesis, we seek solutions to the following two algorithmic pricing problems:
(1) In the first problem, a seller launches a new digital good (this good has unlimited supply and zero marginal cost) but is unaware of its demand in a posted-price setting (i.e., the seller quotes a price to a buyer, and the buyer makes a decision depending on her willingness to pay); we look at the question --- how should the seller set the prices in order to maximize her infinite horizon discounted revenue? This is a classic problem of learning while earning. We propose a few algorithms for this problem and demonstrate their effectiveness using rigorous empirical tests on both synthetic datasets and real-world datasets from auctions at eBay and Yahoo!, and ratings on jokes from Jester, an online joke recommender system. We also show that under certain conditions the myopic Bayesian strategy is also Bayes-optimal. Moreover, this strategy has finite regret (independent of time) which means that it also learns very fast.
(2) The second problem is based on search markets: a consumer is searching for a product sequentially (i.e., she examines possible options one by one and on observing them decides whether to buy or not). However, merely observing a good, although partially informative, does not typically provide the potential purchaser with the complete information set necessary to execute her buying decision. This lack of perfect information about the good creates a market for intermediaries (we refer to them as experts) who can conduct research on behalf of the buyer and sell her this information about the good. The consumer can pay these intermediaries to learn more about the good which can help her in making a better decision about whether to buy the good or not. In this case, we study various pricing schemes for these information intermediaries in a search-based environment (e.g., selling a package of $k$ reports instead of selling a single report or offering a subscription based service). We show how subsidies can be an effective tool for a market designer to increase the social welfare. We also model quality level in the experts and study competition dynamics by computing
equilibrium strategies for the searcher and two experts with different qualities. Surprisingly, sometimes an improvement in the quality of the higher-quality expert (holding everything constant) can be pareto-improving: not only that expert's profit increase, so does the other expert's profit and the searcher's utility.Ph. D.
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Bustamante, Juan Pablo Mamani. "Influência local com procura \"forward\" em modelos de regressão linear." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/104/104131/tde-19012017-112532/.
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A identificação de observações influentes e/ou aberrantes de um conjunto de dados é conhecida como uma parte das análises de diagnóstico. Esta técnica de diagnóstico têm como uma das finalidades verificar a robustez de um modelo estatístico, pois a não identificação dos dados influentes pode afetar a análise ou obter resultados incorretos. As metodologias comumente utilizadas para o diagnóstico de observações influentes em modelos de regressão são métodos de influência global (Belsey et al., 1980). Cook (1986) introduziu um método geral para avaliar a influência local de pequenas perturbações no modelo estatístico ou nos dados, usando diferentes tipos de perturbações. Como complemento às técnicas de detecção de observações discrepantes, é proposto o método procura \\forward\", por Atkinson e Riani (2000), que é uma metodologia para detectar observações atípicas mascaradas. Neste trabalho, propomos o uso da influência local com procura \"forward\" na obtenção de observações mascaradas influentes considerando modelos de regressão linear.The identification of influential and/or atypical observations in a data set is known as a part of the diagnostic analysis. One of the purposes of the diagnostic analysis is to verify the robustness of a statistical model, as the non-identification of influential observations can affect the analysis or may cause the obtainment of incorrect results. The most commonly used methodology for the diagnostic of influential observations in regression models are the global influence (Belsey et al., 1980). Cook (1986) introduced a general method to evaluate the local influence of small perturbations in the statistical model or in the data set using different perturbation schemes. As a complement to the techniques of detection atypical observations, it is proposed the forward search procedure by Atkinson e Riani (2000), which is a methodology to detect the masked atypical observations in a data set. In this work we propose the use of the local influence approach together with the forward search to obtain the masked influential observations in linear regression models.
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Nilsson, Olof. "Visualization of live search." Thesis, Linköpings universitet, Interaktiva och kognitiva system, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-102448.
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The classical search engine result page is used for many interactions with search results. While these are effective at communicating relevance, they do not present the context well. By giving the user an overview in the form of a spatialized display, in a domain that has a physical analog that the user is familiar with, context should become pre-attentive and obvious to the user. A prototype has been built that takes public medical information articles and assigns these to parts of the human body. The articles are indexed and made searchable. A visualization presents the coverage of a query on the human body and allows the user to interact with it to explore the results. Through usage cases the function and utility of the approach is shown.
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Ng, Choon Hoe. "Sensorless vector control of rotary and linear permanent magnet synchronous machines operating at extreme conditions." Thesis, University of Aberdeen, 2003. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU166980.
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Permanent magnet motors are known to provide higher torque and better efficiency than induction motors. They have found applications such as propulsion, motion control, traction, etc in industry. To reduce production costs by eliminating the use of position sensor, many sensorless drive schemes have emerged to fulfil this aim. Most of these sensorless algorithms utilise the back-EMF and magnetic saliency of PM motors to predict the rotor position, which is necessary for any closed loop vector controlled drive implementation. At zero or low speed operation, most sensorless schemes failed to perform well because of the inaccuracy in determining the small induced back-EMF. Contrary, at high-speed, the sampling rate of the rotor position must be sufficiently high. Moreover, the stator resistance varies after prolonged operation due to dissipated heat from the motor, which is significant when the motor is loaded and stalled. The author has proposed several sensorless algorithms to tackle these problems. Compensations are made to take account of the non-linearity of the switching devices in the inverter and the effect of dead time phenomenon. Small signal analyses of PM machine models and systems that include the speed and current regulators are carried out to ensure that they are stable for all operating conditions. Simulations and experimental results are presented to demonstrate that the sensorless drives work in practical implementations. Stability analyses are conducted to verify that the proposed sensorless algorithms are stable in both motoring and regenerating regions.
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Haddow, Barry M. "A study of certain linear connections arising in physical theories with particular reference to holonomy." Thesis, University of Aberdeen, 1993. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU052682.
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The aim of this thesis is to study certain linear connections arising in physics; and in particular metric connections, Weyl connections and Cartan connections are examined. Emphasis is placed on the holonomy group of the connection and the relationships between the relevant geometric objects in the physical theories. The appropriate mathematical background is reviewed in the first two chapters and various notions from differential geometry are introduced. Proofs of theorems relating covariantly constant and recurrent tensors with holonomy are given in detail, and Eisenhart's results on connections induced in submanifolds are given a modern treatment. The relationship between a metric, its Levi-Civita connection and its curvature tensor is examined in chapter three. Some new results on the problem of how to 'recognise' a metric curvature are presented and the idea of a 'curvature copy' - different linear connections with the same curvature - is discussed. Weyl's elegant attempt to unify gravity with electromagnetism is the topic of the fourth chapter. A full holonomy classification of Weyl connections is given in this chapter, along with results concerning the relationship between metric, connection and curvature. The Cartan connection was introduced by Cartan as a device for placing Newtonian gravity in a similar formal setting to Einstein's theory of gravity. This connection is studied in chapter five and reference is made to holonomy properties, symmetries and reduction of the bundle - which enables Newtonian gravity to take on the appearance of a gauge field theory.
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Rossmanith, Gregor [Verfasser], and Gregor [Akademischer Betreuer] Morfill. "Concepts of non-linear data analysis applied to the search of non-Gaussianities in the CMB / Gregor Rossmanith. Betreuer: Gregor Morfill." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2011. http://d-nb.info/1018847197/34.
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Pakusa, Wied [Verfasser], Erich [Akademischer Betreuer] Grädel, Martin [Akademischer Betreuer] Otto, and Anuj [Akademischer Betreuer] Dawar. "Linear equation systems and the search for a logical characterisation of polynomial time / Wied Pakusa ; Erich Grädel, Martin Otto, Anuj Dawar." Aachen : Universitätsbibliothek der RWTH Aachen, 2015. http://d-nb.info/1125910623/34.
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Pakusa, Wied [Verfasser], Erich Akademischer Betreuer] Grädel, Martin [Akademischer Betreuer] Otto, and Anuj [Akademischer Betreuer] [Dawar. "Linear equation systems and the search for a logical characterisation of polynomial time / Wied Pakusa ; Erich Grädel, Martin Otto, Anuj Dawar." Aachen : Universitätsbibliothek der RWTH Aachen, 2015. http://d-nb.info/1125910623/34.
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Pal, Anibrata. "Multi-objective optimization in learn to pre-compute evidence fusion to obtain high quality compressed web search indexes." Universidade Federal do Amazonas, 2016. http://tede.ufam.edu.br/handle/tede/5128.
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CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
The world of information retrieval revolves around web search engines. Text search engines are one of the most important source for routing information. The web search engines index huge volumes of data and handles billions of documents. The learn to rank methods have been adopted in the recent past to generate high quality answers for the search engines. The ultimate goal of these systems are to provide high quality results and, at the same time, reduce the computational time for query processing. Drawing direct correlation from the aforementioned fact; reading from smaller or compact indexes always accelerate data read or in other words, reduce computational time during query processing. In this thesis we study about using learning to rank method to not only produce high quality ranking of search results, but also to optimize another important aspect of search systems, the compression achieved in their indexes. We show that it is possible to achieve impressive gains in search engine index compression with virtually no loss in the final quality of results by using simple, yet effective, multi objective optimization techniques in the learning process. We also used basic pruning techniques to find out the impact of pruning in the compression of indexes. In our best approach, we were able to achieve more than 40% compression of the existing index, while keeping the quality of results at par with methods that disregard compression.
Máquinas de busca web para a web indexam grandes volumes de dados, lidando com coleções que muitas vezes são compostas por dezenas de bilhões de documentos. Métodos aprendizagem de máquina têm sido adotados para gerar as respostas de alta qualidade nesses sistemas e, mais recentemente, há métodos de aprendizagem de máquina propostos para a fusão de evidências durante o processo de indexação das bases de dados. Estes métodos servem então não somente para melhorar a qualidade de respostas em sistemas de busca, mas também para reduzir custos de processamento de consultas. O único método de fusão de evidências em tempo de indexação proposto na literatura tem como foco exclusivamente o aprendizado de funções de fusão de evidências que gerem bons resultados durante o processamento de consulta, buscando otimizar este único objetivo no processo de aprendizagem. O presente trabalho apresenta uma proposta onde utiliza-se o método de aprendizagem com múltiplos objetivos, visando otimizar, ao mesmo tempo, tanto a qualidade de respostas produzidas quando o grau de compressão do índice produzido pela fusão de rankings. Os resultados apresentados indicam que a adoção de um processo de aprendizagem com múltiplos objetivos permite que se obtenha melhora significativa na compressão dos índices produzidos sem que haja perda significativa na qualidade final do ranking produzido pelo sistema.
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Melo, Everton Luiz de. "Meta-heurísticas Iterated Local Search, GRASP e Artificial Bee Colony aplicadas ao Job Shop Flexível para minimização do atraso total." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/3/3136/tde-15122014-002717/.
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O ambiente de produção abordado neste trabalho é o Job Shop Flexível (JSF), uma generalização do Job Shop (JS). O problema de programação de tarefas, ou jobs, no ambiente JS é classificado por Garey; Johnson e Sethi (1976) como NP-Difícil e o JSF é, no mínimo, tão difícil quanto o JS. O JSF é composto por um conjunto de jobs, cada qual constituído por operações. Cada operação deve ser processada individualmente, sem interrupção, em uma única máquina de um subconjunto de máquinas habilitadas. O principal critério de desempenho considerado é a minimização dos atrasos dos jobs. São apresentados modelos de Programação Linear Inteira Mista (PLIM) para minimizar o atraso total e o instante de término da última operação, o makespan. São propostas novas regras de prioridade dos jobs, além de adaptações de regras da literatura. Tais regras são utilizadas por heurísticas construtivas e são aliadas a estratégias cujo objetivo é explorar características específicas do JSF. Visando aprimorar as soluções inicialmente obtidas, são propostas buscas locais e outros mecanismos de melhoria utilizados no desenvolvimento de três meta-heurísticas de diferentes categorias. Essas meta-heurísticas são: Iterated Local Search (ILS), classificada como meta-heurística de trajetória; Greedy Randomized Adaptive Search (GRASP), meta-heurística construtiva; e Artificial Bee Colony (ABC), meta-heurística populacional recentemente proposta. Esses métodos foram selecionados por alcançarem bons resultados para diversos problemas de otimização da literatura. São realizados experimentos computacionais com 600 instâncias do JSF, permitindo comparações entre os métodos de resolução. Os resultados mostram que explorar as características do problema permite que uma das regras de prioridade propostas supere a melhor regra da literatura em 81% das instâncias. As meta-heurísticas ILS, GRASP e ABC chegam a conseguir mais de 31% de melhoria sobre as soluções iniciais e a obter atrasos, em média, somente 2,24% superiores aos das soluções ótimas. Também são propostas modificações nas meta-heurísticas que permitem obter melhorias ainda mais expressivas sem aumento do tempo de execução. Adicionalmente é estudada uma versão do JSF com operações de Montagem e Desmontagem (JSFMD) e os experimentos realizados com um conjunto de 150 instâncias também indicam o bom desempenho dos métodos desenvolvidos.The production environment addressed herein is the Flexible Job Shop (FJS), a generalization of the Job Shop (JS). In the JS environment, the jobs scheduling problem is classified by Garey; Johnson and Sethi (1976) as NP-Hard and the FJS is at least as difficult as the JS. FJS is composed of a set of jobs, each consisting of operations. Each operation must be processed individually, without interruption, in a single machine of a subset of enabled machines. The main performance criterion is minimizing the jobs tardiness. Mixed Integer Linear Programming (MILP) models are presented. These models minimize the total tardiness and the completion time of the last operation, makespan. New priority rules of jobs are proposed, as well as adaptations of rules from the literature. These rules are used by constructive heuristics and are combined with strategies aimed at exploiting specific characteristics of FSJ. In order to improve the solutions initially obtained, local searches and other improvement mechanisms are proposed and used in the development of metaheuristics of three different categories. These metaheuristics are: Iterated Local Search (ILS), classified as trajectory metaheuristic; Greedy Randomized Adaptive Search (GRASP), constructive metaheuristic, and Artificial Bee Colony (ABC), recently proposed population metaheuristic. These methods were selected owing to their good results for various optimization problems in the literature. Computational experiments using 600 FJS instances are carried out to allow comparisons between the resolution methods. The results show that exploiting the characteristics of the problem allows one of the proposed priority rules to exceed the best literature rule in about 81% of instances. Metaheuristics ILS, GRASP and ABC achieve more than 31% improvement over the initial solutions and obtain an average tardiness only 2.24% higher than the optimal solutions. Modifications in metaheuristics are proposed to obtain even more significant improvements without increased execution time. Additionally, a version called Disassembly and Assembly FSJ (DAFJS) is studied and the experiments performed with a set of 150 instances also indicate good performance of the methods developed.
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Liut, Daniel Armando. "Neural-Network and Fuzzy-Logic Learning and Control of Linear and Nonlinear Dynamic Systems." Diss., Virginia Tech, 1999. http://hdl.handle.net/10919/29163.
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The goal of this thesis is to develop nontraditional strategies to provide motion control for different engineering applications. We focus our attention on three topics: 1) roll reduction of ships in a seaway; 2) response reduction of buildings under seismic excitations; 3) new training strategies and neural-network configurations.
The first topic of this research is based on a multidisciplinary simulation, which includes ship-motion simulation by means of a numerical model called LAMP, the modeling of fins and computation of the hydrodynamic forces produced by them, and a neural-network/fuzzy-logic controller. LAMP is based on a source-panel method to model the flowfield around the ship, whereas the fins are modeled by a general unsteady vortex-lattice method. The ship is considered to be a rigid body and the complete equations of motion are integrated numerically in the time domain. The motion of the ship and the complete flowfield are calculated simultaneously and interactively. The neural-network/fuzzy-logic controller can be progressively trained.
The second topic is the development of a neural-network-based approach for the control of seismic structural response. To this end, a two-dimensional linear model and a hysteretic model of a multistory building are used. To control the response of the structure a tuned mass damper is located on the roof of the building. Such devices provide a good passive reduction. Once the mass damper is properly tuned, active control is added to improve the already efficient passive controller. This is achieved by means of a neural network.
As part of the last topic, two new flexible and expeditious training strategies are developed to train the neural-network and fuzzy-logic controllers for both naval and civil engineering applications. The first strategy is based on a load-matching procedure, which seeks to adjust the controller in order to counteract the loads (forces and moments) which generate the motion that is to be reduced. A second training strategy provides training by means of an adaptive gradient search. This technique provides a wide flexibility in defining the parameters to be optimized. Also a novel neural-network approach called modal neural network is designed as a suitable controller for multiple-input multiple output control systems (MIMO).Ph. D.
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Jones, Eric K. "An investigation of the effectiveness of a linear video in informing Kutztown University students of job-search resources and strategies in a career placement office." Instructions for remote access. Click here to access this electronic resource. Access available to Kutztown University faculty, staff, and students only, 1995. http://www.kutztown.edu/library/services/remote_access.asp.
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Thesis (M.S.)--Kutztown University of Pennsylvania, 1995.Source: Masters Abstracts International, Volume: 45-06, page: 2711. Typescript. Abstract appears on leaves 2-3. Includes bibliographical references (leaves 65-67).
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Wang, Jiexin. "Policy Hyperparameter Exploration for Behavioral Learning of Smartphone Robots." 京都大学 (Kyoto University), 2017. http://hdl.handle.net/2433/225744.
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O'Neal, Jerome W. "The use of preconditioned iterative linear solvers in interior-point methods and related topics." Diss., Available online, Georgia Institute of Technology, 2005, 2005. http://etd.gatech.edu/theses/available/etd-06242005-162854/.
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Thesis (Ph. D.)--Industrial and Systems Engineering, Georgia Institute of Technology, 2006.Parker, R. Gary, Committee Member ; Shapiro, Alexander, Committee Member ; Nemirovski, Arkadi, Committee Member ; Green, William, Committee Member ; Monteiro, Renato, Committee Chair.
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Rossini, Wagner Marques. "Identificação de parâmetros de motor de indução linear tubular para extração de petróleo." Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/3/3139/tde-02062008-171921/.
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O presente trabalho apresenta a identificação de parâmetros de motor de indução linear tubular para a extração de petróleo, denominado de MATÆOS -- Motor Assíncrono Tubular para Aplicação na Extração de Óleo Subterrâneo. O primeiro passo para a identificação de parâmetros do motor foi a implementação da bancada de testes com o seu sistema de controle e supervisório. O modelo adotado corresponde à situação de operação em regime estacionário e consiste no circuito contendo resistores e indutores tradicionalmente utilizado para representar motores de indução. A identificação dos parâmetros foi realizada por meio de um procedimento de otimização tomando por base o balanço de potência do motor. Para isso, em função dos parâmetros do modelo, definiu-se e minimizou-se uma medida de erro entre as potências medidas e as calculadas pelo modelo para um conjunto pré-fixado de escorregamentos. A solução desse problema de otimização foi obtida por meio de uma busca exaustiva, uma vez que o número de variáveis independentes do problema é pequeno e uma região contendo o ponto de mínimo é conhecida com razoável confiança. Os resultados obtidos indicam que os valores dos parâmetros nominais a quente apresentam algumas diferenças em relação àqueles produzidos pelo método de identificação. Essas diferenças se devem possivelmente a variações nas características térmicas do motor e a erros introduzidos pelos instrumentos de medida. O modelo identificado apresentou uma menor disponibilidade de força e um pior rendimento quando comparado com os valores de projeto do modelo nominal a quente. Apesar disto, verificou-se uma boa proximidade entre a curva característica do modelo e as obtidas experimentalmente.This work presents the identification of parameters of the tubular linear induction motor for the extraction of oil, called MATÆOS - which is the Portuguese acronym for Asynchronous Tubular Motor for Application to Subterranean Oil Extraction. The first step to the identification of the motor parameters was the implementation of the supervisory and control system for the test bench. The model, which is the usual one containing resistors and inductors, represents the motor operating in steady-state. The parameter identification problem was written as an optimization problem based on the motor power balance. An error between the measured power and the one given by the model was defined and minimized with respect to the model parameters in correspondence to a given set of slipping frequencies. The numerical solution to this problem was obtained by an exhaustive search algorithm. This choice was made because the number of independent variables is small and a region containing the solution is known with a significant degree of confidence. The results obtained show that the nominal values of the model parameters differ slightly from those produced by the identification method. Possibly, such differences are due to the variations in the model caused by temperature changes and to the measurement errors. The identified model presented both a lower available force and a worst efficiency when compared to the nominal design values for the warm motor. Despite this the characteristic curve of the model was quite close to the nominal design one.
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Björklund, Henrik. "Combinatorial Optimization for Infinite Games on Graphs." Doctoral thesis, Uppsala University, Department of Information Technology, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4751.
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Games on graphs have become an indispensable tool in modern computer science. They provide powerful and expressive models for numerous phenomena and are extensively used in computer- aided verification, automata theory, logic, complexity theory, computational biology, etc.
The infinite games on finite graphs we study in this thesis have their primary applications in verification, but are also of fundamental importance from the complexity-theoretic point of view. They include parity, mean payoff, and simple stochastic games.
We focus on solving graph games by using iterative strategy improvement and methods from linear programming and combinatorial optimization. To this end we consider old strategy evaluation functions, construct new ones, and show how all of them, due to their structural similarities, fit into a unifying combinatorial framework. This allows us to employ randomized optimization methods from combinatorial linear programming to solve the games in expected subexponential time.
We introduce and study the concept of a controlled optimization problem, capturing the essential features of many graph games, and provide sufficent conditions for solvability of such problems in expected subexponential time.
The discrete strategy evaluation function for mean payoff games we derive from the new controlled longest-shortest path problem, leads to improvement algorithms that are considerably more efficient than the previously known ones, and also improves the efficiency of algorithms for parity games.
We also define the controlled linear programming problem, and show how the games are translated into this setting. Subclasses of the problem, more general than the games considered, are shown to belong to NP intersection coNP, or even to be solvable by subexponential algorithms.
Finally, we take the first steps in investigating the fixed-parameter complexity of parity, Rabin, Streett, and Muller games.
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Camargo, Fernando Taietti. "Estudo comparativo de passos espectrais e buscas lineares não monótonas." Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/45/45134/tde-16062008-211538/.
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O método do Gradiente Espectral, introduzido por Barzilai e Borwein e analisado por Raydan, para minimização irrestrita, é um método simples cujo desempenho é comparável ao de métodos tradicionais como, por exemplo, gradientes conjugados. Desde a introdução do método, assim como da sua extensão para minimização em conjuntos convexos, foram introduzidas várias combinações de passos espectrais diferentes, assim como de buscas lineares não monótonas diferentes. Dos resultados numéricos apresentados em vários trabalhos não é possível inferir se existem diferenças significativas no desempenho dos diversos métodos. Além disso, também não fica clara a relevância das buscas não monótonas como uma ferramenta em si próprias ou se, na verdade, elas são úteis apenas para permitir que o método seja o mais parecido possível com o método original de Barzilai e Borwein. O objetivo deste trabalho é comparar os diversos métodos recentemente introduzidos como combinações de diferentes buscas lineares não monótonas e diferentes passos espectrais para encontrar a melhor combinação e, a partir daí, aferir o desempenho numérico do método.The Spectral Gradient method, introduced by Barzilai and Borwein and analized by Raydan for unconstrained minimization, is a simple method whose performance is comparable to traditional methods, such as conjugate gradients. Since the introduction of method, as well as its extension to minimization of convex sets, there were introduced various combinations of different spectral steplengths, as well as different nonmonotone line searches. By the numerical results presented in many studies it is not possible to infer whether there are siginificant differences in the performance of various methods. It also is not sure the relevance of the nonmonotone line searches as a tool in themselves or whether, in fact, they are usefull only to allow the method to be as similar as possible with the original method of Barzilai e Borwein. The objective of this study is to compare the different methods recently introduced as different combinations of nonmonotone linear searches and different spectral steplengths to find the best combination and from there, evaluating the numerical performance of the method.
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Waters, Rafael. "Energy from Ocean Waves : Full Scale Experimental Verification of a Wave Energy Converter." Doctoral thesis, Uppsala universitet, Elektricitetslära, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-9404.
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A wave energy converter has been constructed and its function and operational characteristics have been thoroughly investigated and published. The wave energy converter was installed in March of 2006 approximately two kilometers off the Swedish west coast in the proximity of the town Lysekil. Since then the converter has been submerged at the research site for over two and a half years and in operation during three time periods for a total of 12 months, the latest being during five months of 2008. Throughout this time the generated electricity has been transmitted to shore and operational data has been recorded. The wave energy converter and its connected electrical system has been continually upgraded and each of the three operational periods have investigated more advanced stages in the progression toward grid connection. The wave energy system has faced the challenges of the ocean and initial results and insights have been reached, most important being that the overall wave energy concept has been verified. Experiments have shown that slowly varying power generation from ocean waves is possible. Apart from the wave energy converter, three shorter studies have been performed. A sensor was designed for measuring the air gap width of the linear generator used in the wave energy converter. The sensor consists of an etched coil, a search coil, that functions passively through induction. Theory and experiment showed good agreement. The Swedish west coast wave climate has been studied in detail. The study used eight years of wave data from 13 sites in the Skagerrak and Kattegatt, and data from a wave measurement buoy located at the wave energy research site. The study resulted in scatter diagrams, hundred year extreme wave estimations, and a mapping of the energy flux in the area. The average energy flux was found to be approximately 5.2 kW/m in the offshore Skagerrak, 2.8 kW/m in the near shore Skagerrak, and 2.4 kW/m in the Kattegat. A method for evaluating renewable energy technologies in terms of economy and engineering solutions has been investigated. The match between the technologies and the fundamental physics of renewable energy sources can be given in terms of the technology’s utilization. It is argued that engineers should strive for a high utilization if competitive technologies are to be developed.
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Chen, Ting. "Energy-Efficient Resource Allocation in OFDMA Systems." Thesis, Linköpings universitet, Kommunikations- och transportsystem, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-98683.
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In this thesis, a resource allocation problem in OFDMA is studied for the energy efficiency of wireless network. The objective is to minimize the total energy consumption which includes transmission energy consumption, and circuit energy consumption at both transmitter and receiver with required per user’s rate constraint. For problem solution, a heuristic algorithm with low computational complexity and suboptimal solution is proposed, developed in two steps with an increasing order of complexity. Besides, a bounding scheme based on model linearization of formulated nonlinear system model is also proposed to give lower and upper bounds for both small- and large-scale OFDMA network for further algorithm performance evaluation, while the implemented exhaustive search is only capable to provide the optimal solution for small-scale instance for algorithm performance evaluation. Numerical results show that the proposal heuristic algorithm can achieve near-optimal performance with applicable computational complexity even for large-scale networks, and that the bounds from the bounding scheme are very tight for both small- and large-scale OFDMA networks.
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Mazzieri, Diego. "Machine Learning for combinatorial optimization: the case of Vehicle Routing." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/24688/.
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The Vehicle Routing Problem (VRP) is one of the most intensively studied combinatorial optimization problems in the Operations Research (OR) community. Its relevance is not only related to the various real-world applications it deals with, but to its inherent complexity being an NP-hard problem.
From its original formulation more than 60 years ago, numerous mathematical models and algorithms have been proposed to solve VRP. The most recent trend is to leverage Machine Learning (ML) in conjunction with these traditional approaches to enhance their performance.
In particular, this work investigates the use of ML-driven components as destroy or repair methods inside the Large Neighborhood Search (LNS) metaheuristic, trying to understand if, where, and when it is effective to apply them in the context of VRP.
For these purposes, we propose NeuRouting, an open-source hybridization framework aimed at facilitating the integration between ML and LNS.
Regarding the destroy phase, we adopt a Graph Neural Network (GNN) assisted heuristic, which we hybridize with a neural repair methodology taken from the literature. We investigate this integration both on its own and as part of an Adaptive Large Neighborhood Search (ALNS), performing an empirical study on instances of various sizes and against some traditional solvers.
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Khorbatly, Mohamad. "Optimisation numérique appliquée à la gestion de crise : Approche basée sur un algorithme hybride pour la résolution du problème intégré d'ordonnancement et d'allocation des ressources." Thesis, Normandie, 2018. http://www.theses.fr/2018NORMLH18/document.
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Les travaux présentes dans cette thèse s'inscrivent dans le cadre des méthodes d'évacuation des populations. Ils visent à étudier les capacités et modéliser le problème d'évacuation (blessés, sinistrés, enfants, personnes agées, etc.) dans une situation de crise (attentats terroristes, catastrophes naturelles, etc.) et développer des méthodes d'aide à la décision tout en proposant une meilleure planification et des plans optimaux d'évacuation des populations de la zone de crise vers les centres hospitaliers.Notre travail consiste à résoudre le problème d'évacuation de blessés dans des zones de crise avec une nouvelle vision qui consiste à optimiser le temps de transport et par conséquent sauver le maximum des personnes touchées par cette crise d'une façon dynamique, efficace et rapide pour minimiser la perte humaineThe work presented in this thesis is part of human evacuation methods. It aims to study the capacities, model the evacuation problem (wounded, victims, children, elderly, etc.) in a crisis situation (terrorist attacks, natural disasters, etc.) and to develops methods for decision making while proposing better planning and optimal evacuation plans for populations from the crisis zone to hospitals.Our job is to solve the wounded evacuation problem in crisis zone with a new vision that optimizes the transport time and thus saving the maximum of causalities in a dynamic, efficient and fast way in order to minimize human loss
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Cervelin, Bruno Henrique 1988. "Sobre um método de minimização irrestrita baseado em derivadas simplex." [s.n.], 2013. http://repositorio.unicamp.br/jspui/handle/REPOSIP/306038.
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Orientador: Maria Aparecida Diniz EhrhardtDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Matemática Estatística e Computação Científica
Made available in DSpace on 2018-08-22T15:48:00Z (GMT). No. of bitstreams: 1 Cervelin_BrunoHenrique_M.pdf: 1935510 bytes, checksum: 91d17dd60bdd280c9eddd301cb3d2c24 (MD5) Previous issue date: 2013
Resumo: O objetivo deste trabalho é apresentar alguns métodos de minimização irrestrita sem derivadas, tais como, Nelder-Mead, busca padrão e SID-PSM, assim como compará-los. Ainda pretendemos apresentar o problema de otimização de parâmetros de algoritmos, e aplicar o método SID-PSM de modo a encontrar parâmetros ótimos para o próprio método SID-PSM em relação ao número de avaliações de função que o método realiza. Os experimentos numéricos realizados mostram que o SID-PSM _e mais robusto e mais eficiente que os métodos clássicos sem derivadas (busca padrão e Nelder-Mead). Outros experimentos nos mostram o potencial do problema de otimização de parâmetros de algoritmos em melhorar tanto a eficiência quanto a robustez dos métodos
Abstract: The aim of this paper is to present some derivative-free methods for unconstrained minimization problems, such as Nelder-Mead, pattern search and SID-PSM, and compare them. We also intend to present the problem of optimal algorithmic parameters, and apply the method SID-PSM in order to find optimal parameters for the method SID-PSM itself in relation to the number of function evaluations performed by the method. The numerical experiments performed show that the SID-PSM is more robust and more efficient than the classical derivative-free methods (pattern search and Nelder-Mead). Other experiments show us the potential of the problem of optimal algorithmic parameters to improve both the efficiency and the robustness of the methods
Mestrado
Matematica Aplicada
Mestre em Matemática Aplicada
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Silva, Maurício Rodrigues. "Um novo método híbrido aplicado à solução de sistemas não-lineares com raízes múltiplas." Universidade do Estado do Rio de Janeiro, 2009. http://www.bdtd.uerj.br/tde_busca/arquivo.php?codArquivo=1559.
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Este trabalho tem como objetivo apresentar soluções de sistemas não-lineares com raízes múltiplas, através de um algoritmo híbrido. Para esta finalidade foi desenvolvido
e implementado um algoritmo de busca aleatória baseado no método proposto por Luus e Jaakola (1973) como etapa de busca aleatória dos pontos iniciais, que são refinados
através do algoritmo de Hooke e Jeeves. O diferencial deste trabalho foi propor um algoritmo híbrido, utilizando as características dos algoritmos Luus-Jaakola e Hooke e
Jeeves como etapas de busca e refinamento respectivamente. Para isso, os algoritmos acima são encapsulados em funções no algoritmo híbrido. Além destas duas etapas, o algoritmo híbrido possui duas outras características importantes, que é a execução repetida até que se alcance um número suficiente de soluções distintas, que são então submetidas a um processo de classificação de soluções por intervalo, onde cada intervalo gera um conjunto de soluções próximas, que por sua vez, são submetidas à etapa final de minimização, resultando em apenas um valor de solução por classe. Desta forma cada classe produz uma única solução, que faz parte do conjunto final de soluções do problema, pois este algoritmo é aplicado a problemas com múltiplas soluções. Então, o algoritmo híbrido desenvolvido foi testado, tendo como padrão, vários problemas clássicos de programação não-linear, em especial os problemas irrestritos com múltiplas soluções. Após os testes, os resultados foram comparados com o algoritmo Luus-Jaakola, e o Método de Newton Intervalar / Bisseção Generalizada (IN/GB - Interval Newton/Generalized Bisection), com a finalidade de se obter uma
análise quantitativa e qualitativa de seu desempenho. Por fim comprovou-se que o algortimo Híbrido obteve resultados superiores quando comparados com os demais.This paper aims to present solutions for nonlinear systems with multiple roots, using a hybrid algorithm. For this purpose was developed and implemented an algorithm based on random search method proposed by Luus and Jaakola (1973) as a step in search of random starting points, which will be refined through the algorithm of Hooke and Jeeves. The differential of this work is to propose a hybrid algorithm, using the characteristics of the Luus-Jaakola algorithm and Hooke and Jeeves as a search and refinement stages respectively. For this, the above algorithms are encapsulated in functions in the hybrid algorithm. Besides these two steps, the hybrid algorithm has two other important characteristics, which is the execution repeated until to reach a sufficient number of distinct solutions, which is then undergo a process of classification of solutions by interval, where each interval generates a set solutions to close, which in turn is subject to the final stage of minimization, resulting in only one value per class of solution. Thus each class provides a unique solution, which is part of the final set of solutions of the problem, because this algorithm is applied to problems with multiple solutions. So, the hybrid algorithm developed was tested, with the standard, several problems of classical non-linear programming, in particular the unrestricted problems with multiple solutions. After the tests, the results were compared with algorithm Luus-Jaakola, and the Interval Newton/Generalized Bisection method (IN/GB), in order to obtain a quantitative and qualitative analysis of their performance. Finally it was found that the hybrid algortimo achieved higher when compared to the others.
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Farias, Everton da Silveira. "A heuristic approach to supply chain network design in a multi-commodity four-echelon logistics system." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2016. http://hdl.handle.net/10183/140332.
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Nesta tese propõe-se um método heurístico para o problema de Projeto de Rede da Cadeia de Suprimentos (Supply Chain Network Design) considerando vários aspectos de relevância prática, tais como: fornecedores e matérias-primas, localização e operação de instalações, atribuição de Centros de Distribuição (CD), e grande número de clientes e produtos. Uma eficiente abordagem heurística de duas fases é proposta para a obtenção de soluções viáveis para os problemas, que inicialmente é modelado como um Programa Linear Inteiro Misto (PLIM) de grande escala. Na fase de construção, uma estratégia de Linear Programming Rounding é aplicada para se obter os valores iniciais para as variáveis de localização inteira do modelo. Simultaneamente, um método Multi-start foi desenvolvido para gerar soluções iniciais diversificadas para cada nova iteração da heurística de Rounding. Na segunda fase, dois procedimentos de Busca Local foram desenvolvidos no sentido de melhorar a solução fornecida pelo método de Rounding. Implementamos duas diferentes abordagens de Busca Local: remoção-inserção e troca. Uma técnica de Busca Tabu para orientar o procedimento de Busca Local para explorar os diferentes espaços de soluções foi desenvolvida. As formulações e algoritmos foram implementados na linguagem C++ utilizando ferramentas de otimização da COIN-OR. O método de solução foi experimentado em instâncias geradas aleatoriamente, com tamanhos diferentes em termos do número de parâmetros, tais como o número de produtos, zonas de clientes, CDs e fábricas considerando um sistema logístico de quatro níveis. As implementações computacionais mostram que o método de solução proposto obteve resultados satisfatórios quando comparados com a literatura. Para validar este método heurístico também foi usado em um caso realista, com base em dados de uma empresa de borracha que está reestruturando sua cadeia de suprimentos devido ao projeto de uma nova uma nova fábrica e produção de novos produtos. A abordagem heurística proposta revelou-se adequada para aplicação prática em um caso real de uma indústria multicommodity em um contexto determinístico.In this thesis we propose a heuristic method for the Supply Chain Network Design (SCND) problem considering several aspects of practical relevance: suppliers and raw materials, location and operation facilities, distribution center (DC) assignments, and large numbers of customers and products. An efficient two-phase heuristic approach is proposed for obtaining feasible solutions to the problems, which is initially modeled as a large-scale Mixed Integer Linear Program (MILP). In the construction phase, a linear programming rounding strategy is applied to obtain initial values for the integer location variables in the model. Simultaneously, a Multi-start method was developed to generate diversified initial solutions from each new iteration in the rounding heuristic. In the second phase, two Local Search procedures were developed towards to improve the solution provided by the rounding method. We implemented two different Local Search approaches: removal-insertion and exchange. A Tabu Search technique was developed to guide the Local Search procedure to explore the different spaces of solutions. The formulations and algorithms were implemented in C++ code language using the optimization engine COIN-OR. The solution method was experimented in randomly generated instances, with different sizes in terms of the number of parameters, such as number of products, customer zones, DCs, and factories considering a four-echelon logistic system. The computational implementations show that the solution method proposed obtained satisfactory results when compared to the literature review. To validate this heuristic method was also used in a realistic case, based on data from a rubber company that is restructuring its supply chain due to the overture of a new factory, producing new products. The proposed heuristic approach proved appropriate to practical application in a realistic case of a multi commodity industry in a deterministic context.
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Missio, Fabricio Jose. "Equilíbrio com desemprego em um contexto de preços e salários flexíveis : uma abordagem a partir de um modelo não-linear caracterizado como ciclo-limite /." oai:ufpr.br:235189, 2006. http://200.17.209.5:8000/cgi-bin/gw_42_13/chameleon.42.13a?host=localhost%201111%20DEFAULT&sessionid=VTLS&function=CARDSCR&search=KEYWORD&pos=1&u1=12101&t1=235189.
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Orientador : Jose Luis da Costa OreiroDissertação (mestrado) - Universidade Federal do Paraná, Setor de Ciências Sociais Aplicadas, Programa de Pós-Graduação em Desenvolvimento Econômico. Defesa: Curitiba, 2006
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Área de concentração : Políticas públicas
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Le, roux Agnès. "Ordonnancement de rendez-vous en tête à tête." Thesis, Nantes, Ecole des Mines, 2014. http://www.theses.fr/2014EMNA0182/document.
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Les problèmes d’ordonnancement de rendez-vous en tête-à-tête sont des problèmes dans lesquels des personnes souhaitent se rencontrer par deux lors de courts rendez-vous qui se déroulent lors d’une session unique. Dans cette thèse, nous référençons plusieurs applications de ce type de problèmes et proposons des notations qui généralisent les notations standards de problèmes d’ordonnancement α|β|γ. Nous nous intéressons en particulier à un cas dans lequel deux populations distinctes se rencontrent, des participants peuvent arriver en retard et des rencontres sont interdites. L’objectif est de minimiser le nombre maximal d’attentes des participants. Nous étudions dans un premier temps la complexité de ces problèmes : nous démontrons que plusieurs cas sans rencontre interdite sont polynomiaux et que le cas général est NP-complet au sens fort. Nous proposons ensuite des bornes inférieures. Puis nous développons plusieurs méthodes de résolution. Des modèles de programmation linéaire en nombres entiers et un modèle de programmation par contraintes sont tout d’abord proposés. Des règles de dominance permettant de limiter les symétries sont intégrées à ces modèles dans le but de limiter l’espace des solutions. Enfin, nous proposons une recherche à divergence limitée (limited discrepancy search) qui est une méthode approchée basée sur l’exploration d’un arbre de recherche tronqué. Dans cette méthode, nous exploitons le plus possible les propriétés de symétrie du problème pour faciliter la convergence vers une bonne solution. Toutes ces méthodes sont testées et comparées sur un ensemble de 300 instances générées aléatoirement d’après des paramètres réalistesOne-to-one meeting scheduling problems are problems where a population of actors want to meet each other during short time slots that take place in a single session. In this thesis, we reference several applications of this type of problems found in the literature and introduce a notation extending the well-known scheduling notation α|β|γ. We are particularly interested in a case in which two distinct populations meet, participants may arrive late and some meetings are forbidden. The objective is to minimize the maximum number of participants waiting slots. First, we study the complexity of these problems: we show that several cases with no forbidden meeting are polynomial and that the general case is NP-complete in the strong sense. We then propose lower bounds. After that, we develop several resolution methods. Integer linear programming models and a constraint programming model are developed. To limit the solution space, we add dominance rules based on symmetries to these methods. Finally, we present a limited discrepancy search (i.e. an approximate method based on the exploration of a truncated tree search). In this method, we use as much as possible the symmetry properties of the problem to facilitate the convergence to a good solution. All these methods are tested and compared on a set of 300 randomly generated instances from realistic parameters
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May, Lauren Jeanette. "Design, analysis and implementation of symmetric block ciphers." Thesis, Queensland University of Technology, 2002.
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Sehovic, Mirsad, and Markus Carlsson. "Nåbarhetstestning i en baneditor : En undersökning i hur nåbarhetstester kan implementeras i en baneditor samt funktionens potential i att ersätta manuell testning." Thesis, Linnéuniversitetet, Institutionen för datavetenskap (DV), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-36394.
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Denna studie undersöker om det är möjligt att införa nåbarhetstestning i en baneditor. Testets syfte är att ersätta manuell testing, det vill säga att bankonstruktören inte ska behöva spela igenom banan för att säkerställa att denne kommer kunna nå alla nåbara positioner.För att kunna utföra studien skapas en enkel baneditor som testplattform. Vidare utförs en jämförande studie av flera alternativa algoritmer för att fastställa vilken som är mest passande för nåbarhetstestning i en baneditor.Resultatet från den jämförande studien visade att A* (A star) var den mest passande algoritmen för funktionen. Huruvida automatisk testning kan ersätta manuell testning är diskutabelt, men resultatet pekar på en ökad effektivitet i tid när det kommer till banbygge.The following study examines whether it is possible to implement reachability testing in a map editor designed for 2D-platform games. The purpose of reachability testing is to replace manual testing, that being the level designer having to play through the map just to see if the player can reach all supposedly reachable positions in the map.A simple map editor is created to enable the implementation after which we perform a theoretical study in order to determine which algorithm would be best suited for the implementation of the reachability testing.The results comparing algorithms shows that A* (A star) worked best with the function. Whether or not manual testing can be replaced by automatic testing is open for debate, however the results points to an increase in time efficiency when it comes to level design.
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Nahangi, Arian A. "Modeling and Solving the Outsourcing Risk Management Problem in Multi-Echelon Supply Chains." DigitalCommons@CalPoly, 2021. https://digitalcommons.calpoly.edu/theses/2321.
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Worldwide globalization has made supply chains more vulnerable to risk factors, increasing the associated costs of outsourcing goods. Outsourcing is highly beneficial for any company that values building upon its core competencies, but the emergence of the COVID-19 pandemic and other crises have exposed significant vulnerabilities within supply chains. These disruptions forced a shift in the production of goods from outsourcing to domestic methods.
This paper considers a multi-echelon supply chain model with global and domestic raw material suppliers, manufacturing plants, warehouses, and markets. All levels within the supply chain network are evaluated from a holistic perspective, calculating a total cost for all levels with embedded risk. We formulate the problem as a mixed-integer linear model programmed in Excel Solver linear to solve smaller optimization problems. Then, we create a Tabu Search algorithm that solves problems of any size. Excel Solver considers three small-scale supply chain networks of varying sizes, one of which maximizes the decision variables the software can handle. In comparison, the Tabu Search program, programmed in Python, solves an additional ten larger-scaled supply chain networks. Tabu Search’s capabilities illustrate its scalability and replicability.
A quadratic multi-regression analysis interprets the input parameters (iterations, neighbors, and tabu list size) associated with total supply chain cost and run time. The analysis shows iterations and neighbors to minimize total supply chain cost, while the interaction between iterations x neighbors increases the run time exponentially. Therefore, increasing the number of iterations and neighbors will increase run time but provide a more optimal result for total supply chain cost. Tabu Search’s input parameters should be set high in almost every practical case to achieve the most optimal result.
This work is the first to incorporate risk and outsourcing into a multi-echelon supply chain, solved using an exact (Excel Solver) and metaheuristic (Tabu Search) solution methodology. From a practical case, managers can visualize supply chain networks of any size and variation to estimate the total supply chain cost in a relatively short time. Supply chain managers can identify suppliers and pick specific suppliers based on cost or risk. Lastly, they can adjust for risk according to external or internal risk factors.
Future research directions include expanding or simplifying the supply chain network design, considering multiple parts, and considering scrap or defective products. In addition, one could incorporate a multi-product dynamic planning horizon supply chain. Overall, considering a hybrid method combining Tabu Search with genetic algorithms, particle swarm optimization, simulated annealing, CPLEX, GUROBI, or LINGO, could provide better results in a faster computational time.
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Hellberg, Joakim, and Axel Sundkvist. "Comparing Control Strategies fora Satcom on the Move Antenna." Thesis, KTH, Skolan för industriell teknik och management (ITM), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-279331.
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Satellite communication is a widely known method for communicating with remote or disaster-strickenplaces. Sometimes, thecommunication can be a matter of life and death,and it is thus vital that it works well. For two-way communication (such as internet) it is necessary for the antenna on Earth to point towards the satellite with a pointing error not larger than a few tenths of a degree. For example, regulations decided by the authorities in the U.S. forbid pointing errors larger than 0.5°. In some cases the antenna on Earth has to be moving while satellite communication is maintained. Such cases can be when the antenna is mounted to a vehicle, and the antenna thus has to compensate for the vehicle’s movement in order to point at the satellite. This application of satellite communication is called Satcom on the Move (SOTM). By constructing a Simulink model of an entire SOTM-system, including vehicle dynamics, satellite position, signal behavior, sensors, and actuators, different control strategies can be compared. This thesis compares the performance of an H2- and an LQG-controller for a static initial acquisition case, and a dynamic inertial stabilization case. The static initial acquisition case is performed with a search algorithm (SpiralSearch) aiming to find the satellite signalin the shortest possible time for a given initial pointing error. The dynamic inertial stabilization case is performed by allowing the simulated vehicle to drive in a slalom pattern and over uneven grounds. The controllers are designed based on modern control theory.The conclusion of this thesis is that the H2-controller performs slightly better in the static testcase,whereastheLQG-controller performs slightly better in the dynamic test cases. However, the results are greatly influenced by the tuning of the controllers, meaning that the comparison is not necessarily true for the controllers rather than the tuning parameters.Satellitkommunikation är en allmänt känd metod för att kommunicera med avlägsna eller katastrofdrabbade platser. Ibland kan kommunikationen vara en fråga om liv och död, och det är därför viktigt att den fungerar bra. För tvåvägskommunikation (som internet) är det nödvändigt att antennen på jorden pekar mot satelliten med ett pekfel som inte är större än några tiondels grader. Exempelvis finns det lagar i USA som förbjuder pekfel större än 0,5°. I vissa fall måste antennen på jorden röra sig medan satellitkommunikation upprätthålls. Sådana fall kan vara när antennen är monterad på ett fordon och antennen således måste kompensera för fordonets rörelse för att peka mot satelliten. Denna applikation av satellitkommunikation kallas Satcom on the Move(SOTM). Genom att konstruera en simulinkmodell av ett fullständigt SOTM-system, inklusive fordonsdynamik, satellitposition, signalbeteende, sensorer och ställdon, kan olika reglerstrategier jämföras. Denna avhandling jämför en H2 - och en LQG-regulator för ett statiskt fall, samt ett dynamiskt fall. Det statiska fallet utförs med en sökalgoritm (spiralsökning) som syftar till att hitta en specifik satellitsignal på kortast möjliga tid för ett givet initialt pekfel. Det dynamiska fallet utförs genom att låta det simulerade fordonet köra i slalommönster och på ojämnt underlag. Regulatorerna är designade baserade på modern kontrollteori. Slutsatsen av denna avhandling är att H2-regulatorn presterar något bättre i det statiska testfallet, medan LQG-regulatorn presterar något bättre i de dynamiska testfallen. Resultaten påverkas emellertid kraftigt av de designade reglerparametrarna, vilket innebär att jämförelsen inte nödvändigtvis är sann för kontrollerna, utan snarare förde specifika reglerparametrarna.
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Nguyen, Tuan. "Adaptive visual tracking via multiple appearance models and multiple linear searches." Thesis, University of Nottingham, 2015. http://eprints.nottingham.ac.uk/28565/.
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This research is concerned with adaptive, probabilistic single target tracking algorithms. Though visual tracking methods have seen significant improvement, sustained ability to capture appearance changes and precisely locate the target during complex and unexpected motion remains an open problem. Three novel tracking mechanisms are proposed to address these challenges. The first is a Particle Filter based Markov Chain Monte Carlo method with sampled appearances (MCMC-SA). This adapts to changes in target appearance by combining two popular generative models: templates and histograms, maintaining multiple instances of each in an appearance pool. The proposed tracker automatically switches between models in response to variations in target appearance, exploiting the strengths of each model component. New models are added, automatically, as necessary. The second is a Particle Filter based Markov Chain Monte Carlo method with motion direction sampling, from which are derived two variations: motion sampling using a fixed direction of the centroid of all features detected (FMCMC-C) and motion sampling using kernel density estimation of direction (FMCMC-S). This utilises sparse estimates of motion direction derived from local features detected from the target. The tracker captures complex target motions efficiently using only simple components. The third tracking algorithm considered here combines these above methods to improve target localisation. This tracker comprises multiple motion and appearance models (FMCMC-MM) and automatically selects an appropriate motion and appearance model for tracking. The effectiveness of all three tracking algorithms is demonstrated using a variety of challenging video sequences. Results show that these methods considerably improve tracking performance when compared with state of the art appearance-based tracking frameworks.
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Oliveira, José Carlos Francisco de. "Noções de grafos dirigidos, cadeias de Markov e as buscas do Google." Universidade Federal de Sergipe, 2014. https://ri.ufs.br/handle/riufs/6482.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPESThis paper has as its main purpose to highlight some mathematical concepts, which are behind the ranking given by a research made on the website mostly used in the world: Google. At the beginning, we briefly approached some High School’s concepts, such as: Matrices, Linear Systems and Probability. After that, we presented some basic notions related to Directed Graphs and Markov Chains of Discrete Time. From this last one, we gave more emphasis to the Steady State Vector because it ensures foreknowledge results from long-term. These concepts are extremely important to our paper, because they will be used to explain the involvement of Mathematic behind the web search “Google”. Then, we tried to detail the ranking operation of the search pages on Google, i.e., how the results of a research are classified, determining which results are presented in a sequential way in order of relevance. Finally we obtained “PageRank”, an algorithm which creates what we call Google’s Matrices and ranks the pages of a search. We finished making a brief comment about the historical arising of the web searches, from their founders to the rise and hegemony of Google.
O presente trabalho tem como objetivo destacar alguns conceitos matemáticos que estão por trás do ranqueamento dado por uma pesquisa feita no site de busca mais usados do mundo, o “Google”. Inicialmente abordamos de forma breve alguns conteúdos da matemática do ensino médio, a exemplo de: matrizes, sistemas lineares, probabilidades. Em seguida são introduzidas noções básicas de grafos dirigidos e cadeias de Markov de tempo discreto; essa última, é dada uma ênfase ao vetor estado estacionário, por ele garantir resultados de previsão de longo prazo. Esses conceitos são de grande importância em nosso trabalho, pois serão usados para explicar o envolvimento da matemática por trás do site de buscas “Google”. Na sequência, buscamos detalhar o funcionamento do ranqueamento das páginas de uma busca no “Google”, isto é, como são classificados os resultados de uma pesquisa, determinando quais resultados serão apresentados de modo sequencial em ordem de relevância. Finalmente, chegamos na obtenção do “PageRank”, algoritmo que gera a chamada Matriz do Google e ranqueia as páginas de uma busca. Encerramos com um breve histórico do surgimento dos sites de buscas, desde os seus fundadores até a ascensão e hegemonia do Google.
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Possagnolo, Leonardo Henrique Faria Macedo. "Planejamento da expansão de sistemas de distribuição de energia elétrica considerando restauração do fornecimento /." Ilha Solteira, 2019. http://hdl.handle.net/11449/181600.
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Orientador: Rubén Augusto Romero LázaroResumo: A grande maioria dos sistemas de distribuição de energia elétrica opera de forma radial. Isso significa que cada carga é alimentada por apenas uma subestação por meio de um único caminho. Entretanto, as redes de distribuição apresentam estrutura malhada, de forma que, caso uma contingência ocorra, o restabelecimento do fornecimento possa ser realizado para o maior número possível de consumidores. Os trabalhos que lidam com o problema de planejamento da expansão de sistemas de distribuição, no entanto, geralmente consideram a expansão do sistema para apenas uma topologia radial, sem levar em conta aspectos da restauração do fornecimento para melhoria dos índices de confiabilidade. Nesse contexto, este trabalho aborda o planejamento de sistemas de distribuição considerando aspectos econômicos e de confiabilidade, de forma a incluir a restauração do fornecimento no problema de planejamento da expansão. Na formulação do problema considera-se a expansão de novas subestações, o reforço de subestações existentes, a construção de novos alimentadores em novos caminhos, a troca de condutores existentes e a alocação de geradores distribuídos, além de expansão multiestágio e restauração do fornecimento para melhoria dos índices de confiabilidade. Dois métodos alternativos são propostos para resolver o problema descrito: o primeiro considera modelos matemáticos com diversos graus de precisão, para serem resolvidos por métodos exatos, e o segundo é uma meta-heurística de busca e vizinhança... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: The vast majority of electricity distribution systems are operated radially. This means that each load is supplied by only one substation through a single path. However, distribution networks have a meshed structure so that, in the case of a contingency, the supply is restored to as many customers as possible. The works that deal with the distribution systems expansion planning problem, however, generally consider the expansion of the system for only one radial topology, disregarding the restoration aspects to improve reliability indices. In this context, this work deals with the planning of distribution systems considering economic and reliability aspects, to include the service restoration in the planning problem. In the formulation of the problem, it is considered the expansion of new substations, the reinforcement of existing substations, the construction of new feeders in new paths, the exchange of existing conductors, and the allocation of distribution generation, besides multistage expansion and service restoration to improve the reliability indices of the system. Two alternative methods are proposed to solve the described problem: the first one considers relaxed or approximated mathematical models to be solved by exact methods, and the second one is a variable neighborhood search metaheuristic, which solves the complete model for the problem approximately, without guarantee of optimality. The initial solution of the metaheuristic is generated by a strategy that constr... (Complete abstract click electronic access below)
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Jin, Shendan. "Online computation beyond standard models." Electronic Thesis or Diss., Sorbonne université, 2020. http://www.theses.fr/2020SORUS152.
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Dans le cadre standard du calcul en ligne, l’entrée de l’algorithme n’est pas entièrement connue à l’avance, mais elle est révélée progressivement sous forme d’une séquence de requêtes. Chaque fois qu'une requête arrive, l'algorithme en ligne doit prendre des décisions irrévocables pour servir la demande, sans connaissance des requêtes futures. Dans le domaine des algorithmes en ligne, le cadre standard utilisé pour évaluer les performances des algorithmes en ligne est l’analyse compétitive. De manière informelle, le concept d’analyse compétitive consiste à comparer les performances d’un algorithme en ligne dans le pire des cas à une solution optimale hors ligne qui aurait pu être calculée si toutes les données étaient connues d’avance. Dans cette thèse, nous étudierons de nouvelles façons d'approcher les problèmes en ligne. Dans un premier temps, nous étudions le calcul en ligne dans le modèle avec ré-optimisation, dans lequel l'irrévocabilité des décisions en ligne est relâchée. Autrement dit, l'algorithme en ligne est autorisé à revenir en arrière et changer les décisions précédemment prises. Plus précisément, nous montrons comment identifier le compromis entre le nombre de ré-optimisation et les performances des algorithmes en ligne pour le problème de couplage maximale en ligne. De plus, nous étudions des mesures autres que l'analyse compétitive pour évaluer les performances des algorithmes en ligne. Nous observons que parfois, l'analyse compétitive ne peut pas distinguer les performances de différents algorithmes en raison de la nature la plus défavorable du ratio de compétitivité. Nous démontrons qu'une situation similaire se pose dans le problème de la recherche linéaire. Plus précisément, nous revisitons le problème de la recherche linéaire et introduisons une mesure, qui peut être appliquée comme un raffinement du ratio de compétitivité. Enfin, nous étudions le calcul en ligne dans le modèle avec des conseils, dans lequel l'algorithme reçoit en entrée non seulement une séquence de requêtes, mais aussi quelques conseils sur la séquence de requêtes. Plus précisément, nous étudions un modèle récent avec des conseils non fiables, dans lequel les conseils peuvent être fiables ou non. Supposons que dans ce dernier cas, les conseils peuvent être générés à partir d'une source malveillante. Nous montrons comment identifier une stratégie optimale de Pareto pour le problème online bidding dans le modèle de conseil non fiableIn the standard setting of online computation, the input is not entirely available from the beginning, but is revealed incrementally, piece by piece, as a sequence of requests. Whenever a request arrives, the online algorithm has to make immediately irrevocable decisions to serve the request, without knowledge on the future requests. Usually, the standard framework to evaluate the performance of online algorithms is competitive analysis, which compares the worst-case performance of an online algorithm to an offline optimal solution. In this thesis, we will study some new ways of looking at online problems. First, we study the online computation in the recourse model, in which the irrevocability on online decisions is relaxed. In other words, the online algorithm is allowed to go back and change previously made decisions. More precisely, we show how to identify the trade-off between the number of re-optimization and the performance of online algorithms for the online maximum matching problem. Moreover, we study measures other than competitive analysis for evaluating the performance of online algorithms. We observe that sometimes, competitive analysis cannot distinguish the performance of different algorithms due to the worst-case nature of the competitive ratio. We demonstrate that a similar situation arises in the linear search problem. More precisely, we revisit the linear search problem and introduce a measure, which can be applied as a refinement of the competitive ratio. Last, we study the online computation in the advice model, in which the algorithm receives as input not only a sequence of requests, but also some advice on the request sequence. Specifically, we study a recent model with untrusted advice, in which the advice can be either trusted or untrusted. Assume that in the latter case, the advice can be generated from a malicious source. We show how to identify a Pareto optimal strategy for the online bidding problem in the untrusted advice model