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1
Ducamp, Gaspard. "PROCOP : probabilistic rules compilation and optimisation". Electronic Thesis or Diss., Sorbonne université, 2021. http://www.theses.fr/2021SORUS090.
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Adoptées depuis plus de 20 ans par le monde de l’industrie, les règles métiers (business rules) offrent la possibilité à des utilisateurs non-informaticiens de définir des politiques de prise de décision de manière simple et intuitive. Pour faciliter leurs utilisations, des systèmes à base de règles, dits « systèmes de gestion des règles métier », ont été développés, séparant la logique métier de l’application informatique. S’ils sont adaptés pour traiter des données structurées et complètes, ils ne permettent pas aisément de travailler sur des données probabilistes. PROCOP (Probabilistic Rules Optimized and COmPilation) est une thèse proposant une nouvelle approche pour l’intégration de raisonnement probabiliste dans IBM Operational Decision Manager (ODM), le système de gestion des règles métier développé par IBM, notamment via l’introduction d’une notion de risque global sur l'évaluation des conditions d'exécution d'une action, complexifiant la phase de compilation du système mais augmentant l’expressivité des règles métiers. Diverses méthodes sont explorées, implémentées et comparées afin de permettre l'utilisation d'une telle capacité de raisonnement à large échelle, notamment afin de répondre aux problématiques liées à l'utilisation de modèles graphiques probabilistes dans des réseaux complexesWidely adopted for more than 20 years in industrial fields, business rules offer the opportunity to non-IT users to define decision-making policies in a simple and intuitive way. To facilitate their use, rule-based systems, known as business rule management systems, have been developed, separating the business logic from the computer application. While they are suitable for processing structured and complete data, they do not easily allow working with probabilistic data. PROCOP (Probabilistic Rules Optimized and COmPilation) is a thesis proposing a new approach for the integration of probabilistic reasoning in IBM Operational Decision Manager (ODM), IBM's business rules management system, in particular through the introduction of a concept of global risk on the evaluation of the execution conditions of an action, complicating the compilation phase of the system but increasing the expressiveness of the business rules. Various methods are explored, implemented and compared in order to allow the use of such a powerful reasoning capacity on a large scale, in particular in order to answer the problems linked to the use of probabilistic graphical models in complex networks
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Tucker, Dewey S. (Dewey Stanton). "Stochastic realization theory for exact and approximate multiscale models". Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/34468.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.Includes bibliographical references (p. [245]-252).
The thesis provides a detailed analysis of the independence structure possessed by multiscale models and demonstrates that such an analysis provides important insight into the multiscale stochastic realization problem. Multiscale models constitute a broad class of probabilistic models which includes the well--known subclass of multiscale autoregressive (MAR) models. MAR models have proven useful in a variety of different application areas, due to the fact that they provide a rich set of tools for various signal processing tasks. In order to use these tools, however, a MAR or multiscale model must first be constructed to provide an accurate probabilistic description of the particular application at hand. This thesis addresses this issue of multiscale model identification or realization. Previous work in the area of MAR model identification has focused on developing algorithms which decorrelate certain subsets of random vectors in an effort to design an accurate model. In this thesis, we develop a set-theoretic and graph-theoretic framework for better understanding these types of realization algorithms and for the purpose of designing new such algorithms.
(cont.) The benefit of the framework developed here is that it separates the realization problem into two understandable parts - a dichotomy which helps to clarify the relationship between the exact realization problem, where a multiscale model is designed to exactly satisfy a probabilistic constraint, and the approximate realization problem, where the constraint is only approximately satisfied. The first part of our study focuses on developing a better understanding of the independence structure exhibited by multiscale models. As a result of this study, we are able to suggest a number of different sequential procedures for realizing exact multiscale models. The second part of our study focuses on approximate realization, where we define a relaxed version of the exact multiscale realization problem. We show that many of the ideas developed for the exact realization problem may be used to better understand the approximate realization problem and to develop algorithms for solving it. In particular, we propose an iterative procedure for solving the approximate realization problem, and we show that the parameterized version of this procedure is equivalent to the well-known EM algorithm. Finally, a specific algorithm is developed for realizing a multiscale model which matches the statistics of a Gaussian random process.
by Dewey S. Tucker.
Ph.D.
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Cabo, Nodar Marta. "Exact and approximate algorithms for the inventory routing problem". Thesis, University of Southampton, 2003. https://eprints.soton.ac.uk/50599/.
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In this thesis we develop exact and approximate algorithms for the inventory routing problem (IRP). The inventory routing problem is one of deciding an optimal delivery policy for a set of customers through a given planning period. Customers can hold inventory and do not need deliveries every day. Deliveries are carried out by a fleet of homogeneous vehicles that must be routed to travel a minimum distance while visiting all customers scheduled for that day. Decisions concern which customers to be visited and how much to deliver to each of them must be taken. A new formulation for the IRP is presented as a mixed integer programming model. This new approach allows split deliveries so customers can receive the inventory through more than one vehicle during the same day. It also seeks periodic solutions through a given planning period. Although throughout our research the planning period is fixed, all algorithms presented in this thesis can be applied to any length of the planning period. Special cases for this problem are also considered and optimal polynomial algorithms have been developed. We develop four constructive heuristics for the inventory routing problem. These heuristics are based on a schedule-first route-second approach. First, a decision is made on which customers to visit each day, and how much inventory they should receive on each delivery. Then, a vehicle routing problem is solved for each day to perform the deliveries to the customers. Several experiments are carried out to compare the performance of each heuristic. An iterated local search method is then applied to the best solution obtained with these heuristics. The local search is based on node interchange and aims to reduce the number of routes per day as well as the total distance travelled. Extensive computational tests are carried out to asses the effectiveness of this local search procedure.
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Ahern, Zeke Alexander. "Exact and approximate optimisation for strategic bus network planning". Thesis, Queensland University of Technology, 2020. https://eprints.qut.edu.au/206458/1/Zeke_Ahern_Thesis.pdf.
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This thesis contributes to the area of transportation network design at the strategic level, considering objectives for the passenger and operator. The main goal of the research is to improve the existing methods by developing new and more rigorous approaches to integrating route choice, service frequency and adequately accounting for passenger waiting time. An exact model was developed: providing a concise non-ambiguous description to the problem. Case study problem instances found that exact methods implemented by commercial solvers are not scalable for practical problems. Therefore, meta-heuristics were presented to find near-optimal solutions efficiently and demonstrate the practicality of the model in the real-world.
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Markovsky, Ivan. "Exact and approximate modeling of linear systems : a behavioral approach /". Philadelphia, Pa. : Society for Industrial and Applied Mathematics, 2006. http://www.loc.gov/catdir/enhancements/fy0708/2005057537-d.html.
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Taylor, Michael. "Exact and approximate epidemic models on networks : theory and applications". Thesis, University of Sussex, 2013. http://sro.sussex.ac.uk/id/eprint/45258/.
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This thesis is concerned with modelling the spread of diseases amongst host populations and the epidemics that result from this process. We are primarily interested in how networks can be used to model the various heterogeneities observable in real-world populations. Firstly, we start with the full system of Kolmogorov/master equations for a simple Susceptible-Infected-Susceptible (SIS) type epidemic on an arbitrary contact network. From this general framework, we rigorously derive sets of ODEs that describe the exact dynamics of the expected number of individuals and pairs of individuals. We proceed to use moment closure techniques to close these hierarchical systems of ODEs, by approximating higher order moments in terms of lower order moments. We prove that the simple first order mean-field approximation becomes exact in the limit of a large, fully-connected network. We then investigate how well two different pairwise approximations capture the topological features of theoretical networks generated using different algorithms. We then introduce the effective degree modelling framework and propose a model for SIS epidemics on dynamic contact networks by accounting for random link activation and deletion. We show that results from the resulting set of ODEs agrees well with results from stochastic simulations, both in describing the evolution of the network and the disease. Furthermore, we derive an analytic calculation of the stability of the disease-free steady state and explore the validity of such a measure in the context of a dynamically evolving contact network. Finally, we move on to derive a system of ODEs that describes the interacting dynamics of a disease and information relating to the disease. We allow individuals to become responsive in light of received information and, thus, reduce the rate at which they become infected. We consider the effectiveness of different routes of information transmission (such as peer-to-peer communication or mass media campaigns) in slowing or preventing the spread of a disease. Finally, we use a range of modelling techniques to investigate the spread of disease within sheep flocks. We use field data to construct weighted contact networks for flocks of sheep to account for seasonal changes of the flock structure as lambs are born and eventually become weaned. We construct a range of network and ODE models that are designed to investigate the effect of link-weight heterogeneity on the spread of disease.
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Igwe, Tobenna. "An empirical study on computation of exact and approximate equilibria". Thesis, University of Liverpool, 2018. http://livrepository.liverpool.ac.uk/3016935/.
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The computation of Nash equilibria is one of the central topics in game theory, which has received much attention from a theoretical point of view. Studies have shown that the problem of finding a Nash equilibrium is PPAD-complete, which implies that we are unlikely to find a polynomial-time algorithm for this problem. Naturally, this has led to a line of work studying the complexity of finding approximate Nash equilibria. This thesis examines the computation of such approximate Nash equilibria within several classes of games from an empirical perspective. In this thesis, we address the computation of approximate Nash equilibria in bimatrix and polymatrix games. For both of these game classes, we provide a library of implementations of algorithms for the computation of exact and approximate Nash equilibria, as well as a suite of game generators which were used as a base for our empirical analysis of the algorithms. We investigate the trade-off between quality of approximation produced by the algorithms and the expected runtime. We provide some insight into the inner workings of the state-of-the-art algorithm for computing ε-Nash equilibria, presenting worst-case examples found for our provided suite of game generators. We then show lower bounds on these algorithms. In the case of polymatrix games, we generate this lower bound from a real-world application of game theory. For bimatrix games, we provide a robust means of generating lower bounds for approximation algorithms with the use of genetic algorithms.
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Diaz, Bobillo Ignacio Javier. "The general â₁ optimal multiblock problem : exact and approximate solutions". Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/12798.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1992.Includes bibliographical references (leaves 119-123).
by Ignacio Javier Diaz-Bobillo.
Ph.D.
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Hassan, Abdeljabbar Hassan Mohammed Albarra. "Parallel Scheduling in the Cloud Systems : Approximate and Exact Methods". Thesis, Université de Lorraine, 2016. http://www.theses.fr/2016LORR0223/document.
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Cette thèse porte sur la résolution exacte et heuristique de plusieurs problèmes ayant des applications dans le domaine de l'Informatique dématérialisé (cloud computing). L'Informatique dématérialisée est un domaine en plein extension qui consiste à mutualiser les machines/serveurs en définissant des machines virtuelles représentant des fractions des machines/serveurs. Il est nécessaire d'apporter des solutions algorithmiques performantes en termes de temps de calcul et de qualité des solutions. Dans cette thèse, nous nous sommes intéressés dans un premier temps au problème d'ordonnancement sur plusieurs machines (les machines virtuelles) avec contraintes de précédence, c.-à-d., que certaines tâches ne peuvent s'exécuter que si d'autres sont déjà finies. Ces contraintes représentent une subdivision des tâches en sous tâches pouvant s'exécuter sur plusieurs machines virtuelles. Nous avons proposé plusieurs algorithmes génétiques permettant de trouver rapidement une bonne solution réalisable. Nous les avons comparés avec les meilleurs algorithmes génétiques de la littérature et avons défini les types d'instances où les solutions trouvées sont meilleures avec notre algorithme. Dans un deuxième temps, nous avons modélisé ce problème à l'aide de la programmation linéaire en nombres entiers permettant de résoudre à l'optimum les plus petites instances. Nous avons proposé de nouvelles inégalités valides permettant d'améliorer les performances de notre modèle. Nous avons aussi comparé cette modélisation avec plusieurs formulations trouvées dans la littérature. Dans un troisième temps, nous avons analysé de manière approfondie la sous-structure du sous-graphe d'intervalle ne possédant pas de clique de taille donnée. Nous avons étudié le polytope associé à cette sous-structure et nous avons montré que les facettes que nous avons trouvées sont valides pour le problème d'ordonnancement sur plusieurs machines avec contraintes de précédence mais elles le sont aussi pour tout problème d'ordonnancement sur plusieurs machines. Nous avons étendu la modélisation permettant de résoudre le précédent problème afin de résoudre le problème d'ordonnancement sur plusieurs machines avec des contraintes disjonctives entre les tâches, c.-à-d., que certaines tâches ne peuvent s'exécuter en même temps que d'autres. Ces contraintes représentent le partage de ressources critiques ne pouvant pas être utilisées par plusieurs tâches. Nous avons proposé des algorithmes de séparation afin d'insérer de manière dynamique nos facettes dans la résolution du problème puis avons développé un algorithme de type Branch-and-Cut. Nous avons analysé les résultats obtenus afin de déterminer les inégalités les plus intéressantes afin de résoudre ce problème. Enfin dans le dernier chapitre, nous nous sommes intéressés au problème d'ordonnancement d'atelier généralisé ainsi que la version plus classique d'ordonnancement d'atelier (open shop). En effet, le problème d'ordonnancement d'atelier généralisé est aussi un cas particulier du problème d'ordonnancement sur plusieurs machines avec des contraintes disjonctives entre les tâches. Nous avons proposé une formulation à l'aide de la programmation mathématique pour résoudre ces deux problèmes et nous avons proposé plusieurs familles d'inégalités valides permettant d'améliorer les performances de notre algorithme. Nous avons aussi pu utiliser les contraintes définies précédemment afin d'améliorer les performances pour le problème d'ordonnancement d'atelier généralisé. Nous avons fini par tester notre modèle amélioré sur les instances classiques de la littérature pour le problème d'ordonnancement d'atelier. Nous obtenons de bons résultats permettant d'être plus rapide sur certaines instancesThe Cloud Computing appears as a strong concept to share costs and resources related to the use of end-users. As a consequence, several related models exist and are widely used (IaaS, PaaS, SaaS. . .). In this context, our research focused on the design of new methodologies and algorithms to optimize performances using the scheduling and combinatorial theories. We were interested in the performance optimization of a Cloud Computing environment where the resources are heterogeneous (operators, machines, processors...) but limited. Several scheduling problems have been addressed in this thesis. Our objective was to build advanced algorithms by taking into account all these additional specificities of such an environment and by ensuring the performance of solutions. Generally, the scheduling function consists in organizing activities in a specific system imposing some rules to respect. The scheduling problems are essential in the management of projects, but also for a wide set of real systems (telecommunication, computer science, transportation, production...). More generally, solving a scheduling problem can be reduced to the organization and the synchronization of a set of activities (jobs or tasks) by exploiting the available capacities (resources). This execution has to respect different technical rules (constraints) and to provide the maximum of effectiveness (according to a set of criteria). Most of these problems belong to the NP-Hard problems class for which the majority of computer scientists do not expect the existence of a polynomial exact algorithm unless P=NP. Thus, the study of these problems is particularly interesting at the scientific level in addition to their high practical relevance. In particular, we aimed to build new efficient combinatorial methods for solving parallel-machine scheduling problems where resources have different speeds and tasks are linked by precedence constraints. In our work we studied two methodological approaches to solve the problem under the consideration : exact and meta-heuristic methods. We studied three scheduling problems, where the problem of task scheduling in cloud environment can be generalized as unrelated parallel machines, and open shop scheduling problem with different constraints. For solving the problem of unrelated parallel machines with precedence constraints, we proposed a novel genetic-based task scheduling algorithms in order to minimize maximum completion time (makespan). These algorithms combined the genetic algorithm approach with different techniques and batching rules such as list scheduling (LS) and earliest completion time (ECT). We reviewed, evaluated and compared the proposed algorithms against one of the well-known genetic algorithms available in the literature, which has been proposed for the task scheduling problem on heterogeneous computing systems. Moreover, this comparison has been extended to an existing greedy search method, and to an exact formulation based on basic integer linear programming. The proposed genetic algorithms show a good performance dominating the evaluated methods in terms of problems' sizes and time complexity for large benchmark sets of instances. We also extended three existing mathematical formulations to derive an exact solution for this problem. These mathematical formulations were validated and compared to each other by extensive computational experiments. Moreover, we proposed an integer linear programming formulations for solving unrelated parallel machine scheduling with precedence/disjunctive constraints, this model based on the intervaland m-clique free graphs with an exponential number of constraints. We developed a Branch-and-Cut algorithm, where the separation problems are based on graph algorithms. [...]
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Almoustafa, Samira. "Distance-constrained vehicle routing problem : exact and approximate solution (mathematical programming)". Thesis, Brunel University, 2013. http://bura.brunel.ac.uk/handle/2438/7640.
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The asymmetric distance-constrained vehicle routing problem (ADVRP) looks at finding vehicle tours to connect all customers with a depot, such that the total distance is minimised; each customer is visited once by one vehicle; every tour starts and ends at a depot; and the travelled distance by each vehicle is less than or equal to the given maximum value. We present three basic results in this thesis. In the first one, we present a general flow-based formulation to ADVRP. It is suitable for symmetric and asymmetric instances. It has been compared with the adapted Bus School Routing formulation and appears to solve the ADVRP faster. Comparisons are performed on random test instances with up to 200 customers. We reach a conclusion that our general formulation outperforms the adapted one. Moreover, it finds the optimal solution for small test instances quickly. For large instances, there is a high probability that an optimal solution can be found or at least improve upon the value of the best feasible solution found so far, compared to the other formulation which stops because of the time condition. This formulation is more general than Kara formulation since it does not require the distance matrix to satisfy the triangle inequality. The second result improves and modifies an old branch-and-bound method suggested by Laporte et al. in 1987. It is based on reformulating a distance-constrained vehicle routing problem into a travelling salesman problem and uses the assignment problem as a lower bounding procedure. In addition, its algorithm uses the best-first strategy and new branching rules. Since this method was fast but memory consuming, it would stop before optimality is proven. Therefore, we introduce randomness in choosing the node of the search tree in case we have more than one choice (usually we choose the smallest objective function). If an optimal solution is not found, then restart is required due to memory issues, so we restart our procedure. In that way, we get a multistart branch and bound method. Computational experiments show that we are able to exactly solve large test instances with up to 1000 customers. As far as we know, those instances are much larger than instances considered for other VRP models and exact solution approaches from recent literature. So, despite its simplicity, this proposed algorithm is capable of solving the largest instances ever solved in literature. Moreover, this approach is general and may be used in solving other types of vehicle routing problems. In the third result, we use VNS as a heuristic to find the best feasible solution for groups of instances. We wanted to determine how far the difference is between the best feasible solution obtained by VNS and the value of optimal solution in order to use the output of VNS as an initial feasible solution (upper bound procedure) to improve our multistart method. Unfortunately, based on the search strategy (best first search), using a heuristic to find an initial feasible solution is not useful. The reason for this is because the branch and bound is able to find the first feasible solution quickly. In other words, in our method using a good initial feasible solution as an upper bound will not increase the speed of the search. However, this would be different for the depth first search. However, we found a big gap between VNS feasible solution and an optimal solution, so VNS can not be used alone unless for large test instances when other exact methods are not able to find any feasible solution because of memory or stopping conditions.
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Cappadonna, Fulvio Antonio. "Application of exact and approximate optimization methods to novel scheduling problems". Doctoral thesis, Università di Catania, 2014. http://hdl.handle.net/10761/1482.
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The application of exact and heuristic optimization techniques to scheduling problems pertaining to production processes has been widely investigated over the last decades by the relevant scientific literature in the field of industrial systems design and analysis. In general, the term scheduling is used with reference to the allocation of resources to tasks over time, so to execute all planned activities according to a given performance objective (minimization of costs, minimization of production time, due dates fulfilment, etc.). Even though basic scheduling problems have been effectively solved long time ago, this topic still remains attractive for expert and practitioners, as the technological innovation of production processes and the need for effective planning activities emerging from new sectors still set new frontiers to the scheduling optimization research.
The aim of the present Thesis is to investigate three scheduling problems that have not been addressed yet by the literature, even though they have a clear correspondence to real-world manufacturing environments.
The first problem addressed is the minimization of makespan in an unrelated parallel machine system with sequence-dependent setup times and limited human resources. Workers are needed to perform setup operations before each job is processed; they are supposed to be a critical resource as their number is assumed to be lower than the number of workstations available in the production shop. In addition, each worker is characterized by a provided skill level, which affects the time required for completing setup operations. Firstly, a Mixed Integer Linear Programming (MILP) model suitable for tackling small instances of the problem in hand is illustrated. Then, an optimization framework based on Genetic Algorithms (GAs) is presented with the aim of effectively addressing larger test cases. Three different procedures are proposed, namely a permutation based GA, a multi-encoding GA, and a hybrid GA. An extensive benchmark including both small-and large-sized instances is taken as reference for both calibration and comparison of the proposed methods, which have been performed by means of ANOVA analysis.
The second problem addressed is the minimization of makespan in a Flow Shop Sequence Dependent Group Scheduling (FSDGS) problem entailing the worker allocation issue. As first, a Mixed Integer Linear Programming (MILP) formulation for the problem is given. Then, a well-known benchmark arisen from literature is adopted for carrying out an extensive comparison campaign among three specifically developed metaheuristic methods based on a GA framework. Afterwards, the best procedure among those tested is compared with a well-performing algorithm recently proposed in the field of FSDGS problems.
The third problem addressed is the minimization of makespan in a hybrid flow shop inspired to a truly observed micro-electronics manufacturing environment, is illustrated. Overlap between jobs, waiting time limit of jobs within inter-stage buffers as well as machine unavailability time intervals represent just a part of the constraints which characterize the problem here investigated. A MILP model of the problem has been developed with the aim to validate the performance concerning the proposed optimization technique, based on a two-phase metaheuristics (MEs). In the first phase the proposed ME algorithm evolves similarly to a genetic algorithm equipped with a regular permutation encoding. Subsequently, a random search algorithm equipped with an m-stage permutation encoding is launched for improving the algorithm strength in terms of both exploration and exploitation. Extensive numerical studies on a benchmark of problems, along with a properly arranged ANOVA analysis, demonstrate the statistical outperformance of the proposed approach with respect to the traditional optimization approach based on a single encoding.
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Naujoks, Rouven Verfasser] y Kurt [Akademischer Betreuer] [Mehlhorn. "NP-hard networking problems : exact and approximate algorithms / Rouven Naujoks. Betreuer: Kurt Mehlhorn". Saarbrücken : Saarländische Universitäts- und Landesbibliothek, 2011. http://d-nb.info/1051324181/34.
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Jeter, Jennifer. "Comparison between the exact and the approximate bandwidths in the kernel density estimation /". Available to subscribers only, 2005. http://proquest.umi.com/pqdweb?did=1079660721&sid=7&Fmt=2&clientId=1509&RQT=309&VName=PQD.
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Edirisuriya, Amila. "Digital Hardware Architectures for Exact and Approximate DCT Computation Using Number Theoretic Techniques". University of Akron / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=akron1363233037.
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Naujoks, Rouven [Verfasser] y Kurt [Akademischer Betreuer] Mehlhorn. "NP-hard networking problems : exact and approximate algorithms / Rouven Naujoks. Betreuer: Kurt Mehlhorn". Saarbrücken : Saarländische Universitäts- und Landesbibliothek, 2011. http://d-nb.info/1051324181/34.
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Chien, Ying-Che. "Some exact and approximate methods for large scale systems steady-state availability analysis". Diss., The University of Arizona, 1995. http://hdl.handle.net/10150/187066.
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System availability is the probability of the system being operable at instant t. Markov chains are a model used for system availability analysis. The exact analytical solution in terms of component failure rates and repair rates for steady-state system availability is complex to find solving the large numbers of simultaneous linear equations that result from the model. Although exact analytical solutions have been developed for series and parallel systems and for some other small size systems, they have not been developed for large scale general systems with n distinct components. Some methods for approximate analytical solutions have been suggested, but limitations on network types, over simplified states merge conditions and lack of predictions of approximation errors make these methods difficult to use. Markov state transition graphs can be classified as symmetric or asymmetric. A symmetric Markov graph has two-way transitions between each pair of communicating nodes. An asymmetric Markov graph has some pair(s) of communicating nodes with only one-way transitions. In this research, failure rates and repair rates are assumed to be component dependent only. Exact analytical solutions are developed for systems with symmetric Markov graphs. Pure series systems, pure parallel systems and general k out of n systems are examples of systems with symmetric Markov graphs. Instead of solving a large number of linear equations from the Markov model to find the steady-state system availability, it is shown that only algebraic operations on component failure rates and repair rates are necessary. In fact, for the above class of systems, the exact analytical solutions are relatively easy to obtain. Approximate analytical solutions for systems with asymmetric Markov graphs are also developed based on the exact solutions for the corresponding symmetric Markov graphs. The approximate solutions are shown to be close to the exact solutions for large scale and complex systems. Also, they are shown to be lower bounds for the exact solutions. Design principles to improve systems availability are derived from the analytical solutions for systems availability. Important components can be found easily with the iteration procedure and computer programs provided in this research.
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Boland, Matthew R. "Examination of the use of exact versus approximate phase weights on the performance of a synthetic aperture sonar system". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2003. http://library.nps.navy.mil/uhtbin/hyperion-image/03Mar%5FBoland.pdf.
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Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, March 2003.Thesis advisor(s): Lawrence J. Ziomek, Ziaoping Yun. Includes bibliographical references (p. 63). Also available online.
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Uriguen, Garaizabal Jose Antonio. "Exact and approximate Strang-Fix conditions to reconstruct signals with finite rate of innovation from samples taken with arbitrary kernels". Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/12817.
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In the last few years, several new methods have been developed for the sampling and exact reconstruction of specific classes of non-bandlimited signals known as signals with finite rate of innovation (FRI). This is achieved by using adequate sampling kernels and reconstruction schemes. An example of valid kernels, which we use throughout the thesis, is given by the family of exponential reproducing functions. These satisfy the generalised Strang-Fix conditions, which ensure that proper linear combinations of the kernel with its shifted versions reproduce polynomials or exponentials exactly. The first contribution of the thesis is to analyse the behaviour of these kernels in the case of noisy measurements in order to provide clear guidelines on how to choose the exponential reproducing kernel that leads to the most stable reconstruction when estimating FRI signals from noisy samples. We then depart from the situation in which we can choose the sampling kernel and develop a new strategy that is universal in that it works with any kernel. We do so by noting that meeting the exact exponential reproduction condition is too stringent a constraint. We thus allow for a controlled error in the reproduction formula in order to use the exponential reproduction idea with arbitrary kernels and develop a universal reconstruction method which is stable and robust to noise. Numerical results validate the various contributions of the thesis and in particular show that the approximate exponential reproduction strategy leads to more stable and accurate reconstruction results than those obtained when using the exact recovery methods.
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King, Gerald D. 1974. "Presentation and comparision of an exact structural analysis code with the MIT design method and the coupled wall approximate deflection analysis procedure". Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/49986.
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Pommer, Wagner Marcelo. "A construção de significados dos números irracionais no ensino básico: uma proposta de abordagem envolvendo os eixos constituintes dos números reais". Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/48/48134/tde-23082012-092642/.
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Considerando-se como fonte primária os manuais escolares brasileiros de Matemática, o saber a ser ensinado ainda situa uma apresentação dual, polarizado no viés pragmático ou teórico, ao que se segue um procedimento temático padrão que privilegia o desenvolvimento operatório envolvendo contextos exatos, finitos e determinísticos. Em particular, essas características se acentuam gravemente no momento de introdução dos números irracionais no ensino básico, o que ocasiona uma abordagem restritiva. Para superar este quadro, Bruner (1987) fundamenta que não devemos adiar o ensino de assuntos essenciais com base na crença de que são difíceis demais, pois as ideias fundamentais de qualquer assunto podem ser ensinadas na escolaridade básica, porém demanda um trabalho para além dos aspectos técnicos, o que equivale a retomada de características ligadas à compreensão. Neste trabalho, tivemos por hipótese que os pares discreto/contínuo; exato/aproximado; finito/infinito, presentes na análise da evolução epistemológica dos números reais e descritos em Machado (2009), se constituem em pilares conceituais essenciais para fundamentar um panorama favorável a uma abordagem significativa do tema dos números irracionais, de modo a compor um amálgama entre os aspectos técnicos e semânticos. Em face da necessária reflexão, em nível educacional, em torno de tal tema, delimitamos inicialmente um contexto investigativo pautado em um estudo qualitativo orientado pela questão Como são abordados os números irracionais no ensino básico, considerando-se como fonte o livro didático de Matemática?, a fim de mapear a apresentação deste assunto no Ensino Fundamental II e no Ensino Médio. O fundamento metodológico se inspirou nos núcleos de significação, descritos em Aguiar&Ozella (2006), que buscou apreender os sentidos que constituem o conteúdo do discurso expresso nos textos dos livros didáticos. O percurso dos núcleos de significação confirmou que, nos livros didáticos analisados, a apresentação dos números irracionais ocorre de modo polarizado: alguns optam por um viés empírico e outros pela definição formal. Verificou-se que, após uma abordagem inicial, não ocorre intercâmbio destas opções, o que acarreta um rápido esgotamento das ferramentas para se desenvolver as temáticas, limitando a compreensão da complexidade dos números irracionais no ensino básico. A partir das hipóteses e da pesquisa empírica, nos propusemos a delinear as contribuições presentes no movimento dialético entre os pares discreto/contínuo, finito/infinito e exato/aproximado, cujas mútuas conexões permeiam um espaço de significações, um campo que possibilita organizar, tecer e ampliar a rede de significados, conforme Machado (1995), favorecendo um quadro de maior compreensão à apresentação dos números irracionais. O enfoque epistemológico realizado revelou uma multiplicidade de relações envolvendo os números irracionais e diversos assuntos do currículo de Matemática, não devidamente caracterizadas e exploradas no ensino básico, o que serviu de mote para a apresentação de algumas situações de ensino para ilustrar os aportes orientadores sugeridos. Acreditamos que o caminho epistemológico trilhado viabilizou uma abertura para ampliar o quadro de significados em relação a outros tópicos presentes na Matemática Elementar, considerando-se como suporte a potencialidade presente nos eixos discreto/contínuo; exato/aproximado; finito/infinito, assim como no par determinístico/aleatório.Considering Brazilian mathematics school textbooks as a primary research source, the knowledge to be taught still has a dual presentation, polarized in a pragmatic or theoretical way, what follows a thematic procedure pattern that favors an operational development involving exact, finite and deterministic contexts. In particular, these characteristics are seriously accentuated by the time of irrational numbers introduction at basic education, which leads to a restrictive approach. To overcome this situation, Bruner (1987) states that we should not postpone teaching key issues based on the belief that they are too hard, because the fundamental ideas of any subject can be taught at basic education, but it demands a work that overcome technical aspects, considerations that are equivalent to the resumption with aspects related to understanding. In this work, we had by hypothesis that the tension inherent on discrete/continuous, exact/approximate, finite/infinite pairs, extracted from analyses on real numbers epistemological evolution and described at Machado (2009), constitutes an essential conceptual pillar to establish a helpful framework to enable a significant irrational numbers approach, in order to compose an amalgam between technical and semantic aspects. Considering the necessary educational discussion involving this theme, we initially delimited an investigative context based on a qualitative study guided by the question How irrational numbers are approached in basic education, considering mathematics textbook as a source?\' in order to map this subject presentation at Middle and High School. The methodological foundation was inspired in meaning core, described in Aguiar and Ozella (2006), which aims to capture the sense that constitutes the speech content expressed inside mathematics scholar textbooks. The analysis from meaning core route reveals that, in the textbooks examined, the most known irrational numbers introduction occurs in a polarized way: some opt for a pragmatic bias and others by formal definition. However, it was found that after an initial approach, there is no further relationship between these options, which causes a rapid depletion of the tools to develop these themes, which limits the complexity understanding of irrational numbers in basic education. From the hypotheses and the empirical research, we intended to delineate contributions presented on the dialectical movement between discrete/continuous, finite/infinite and exact/approximate pairs, whose mutual connections permeate a \'space of meanings\', a field that allows to organize, to weave and to expand a network of meanings, as Machado (1995), favoring a framework for better understanding the irrational numbers development in basic school. The epistemological approach performed revealed a multiplicity of relationships involving irrational numbers and various subjects of mathematics curriculum, not properly characterized and exploited in basic education, references which served as contexts for the presentation of some teaching situations to illustrate the contributions guidance suggested. We believe that the epistemological path trodden enables an opening to increase possibilities of meanings in relation to other topics of Elementary Mathematics, considering as support the capability constituents presented in discrete/continuous, exact/approximate, finite/infinity axis, as well as in deterministic/random pair.
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Li, Chi-Rong y 李其融. "Exact Inferences on Paired ROC Curves". Thesis, 2007. http://ndltd.ncl.edu.tw/handle/79396488704560563679.
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博士國立臺灣大學
農藝學研究所
95
The receiver operating characteristic (ROC) curve is currently a popular statistical tool for the accuracy of diagnostic device. It has been widely used in various practical applications, such as radiology, psychiatry, epidemiology, biomedical informatics, etc. One of the primary objectives of diagnostic trials is to compare the diagnostic accuracy of the new diagnostic device to that of the current standard device. The area under the ROC curve (AUROC) is a summary index that is interpreted as the average of true positive rate over entire false positive rates. The partial area under the ROC curve (PAUROC) is another summary index that restricts attention to a specified range of clinical interest. They can be usually used as the bases of inferential statistics for comparing ROC curves. In this dissertation, we develop exact inferences for comparing paired AUROCs and paired PAUROCs based on the concept of generalized p-values and generalized confidence intervals. In addition, we extend the results to compare the paired ROC curves which are constructed by multiple markers. Simulation results demonstrate that the exact test based on generalized p-values adequately controls the size at the nominal level; the exact interval estimation based on the generalized confidence intervals provides not only sufficient coverage probability but also reasonable expected length. In general, the proposed methods outperform some published asymptotic maximum likelihood methods and nonparametric methods in various simulation scenarios. Furthermore, numerical examples using published datasets illustrate the proposed methods.
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Li, Chi-Rong. "Exact Inferences on Paired ROC Curves". 2007. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0001-2407200718554300.
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Lu, Chia Wei y 呂嘉維. "Efficient Exact and Approximate String Matching Algorithms". Thesis, 2014. http://ndltd.ncl.edu.tw/handle/49922113552090356808.
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博士國立清華大學
資訊工程學系
102
In this thesis, we first propose two algorithms for exact string matching problem, which aims to find all the positions i's in a given text where a given pattern occurs. Our algorithms find an optimal selective comparing order of the characters of the pattern so that we could have a better performance in the searching phase. To find the optimal comparing order, we adopt the branch and bound approach. Moreover, our proposed algorithm can be combined with other existing exact string matching algorithms to improve the searching efficiency. The experimental results show that our algorithms indeed have the smallest number of character comparisons and are also efficient in time as compared with other existing exact string matching algorithms. Second, we propose a new filtration algorithm, as well as a hybrid filtration strategy, to efficiently solve the approximate string matching problem (also called the k-difference problem), which aims to find all the positions i's in a given text such that there exists a substring of the text ending at position i whose edit distance from a given pattern is less than or equal to a given error bound k. Our experimental results on simulated datasets of DNA sequences show that when compared with other filtration algorithms, our filtration algorithm has better performance on the efficiency to filter out those positions of the text at which the pattern does not occur approximately. Moreover, our hybrid filtration strategy further improves the effectiveness of our filtration algorithm. Third, we propose a progressive approach to solve the DNA resequencing problem which is defined as follows: We are given an unknown DNA sequence X and a known reference sequence R. Our task is to see whether X and R are similar or not. The present popular approach is to break up X into subsequences by the next generation sequencing (NGS) technologies, called reads. We then map the reads of X onto R with a suitable error bound. However, if the similarity between X and R is not very high (<95%), there would be many reads unmapped, and we then cannot obtain the mutations inside the unmapped regions. One can use a large error bound to increase the number of reads mapped. But it is not a good solution because increasing error bound will also increase the probability of false positive mapping. Our approach uses a small error bound and to increase the number of reads mapped, our approach modifies R each time after the reads are mapped. Thus our approach is a progressive approach. Compared with other available tools, our approach allows us to be able to map more reads to the reference sequence. In our simulated experiments, we also show the high correctness of our mapping algorithm.
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Chang, Yin-Wen. "Exact and Approximate Methods for Machine Translation Decoding". Thesis, 2015. https://doi.org/10.7916/D8JM294G.
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Statistical methods have been the major force driving the advance of machine translation in recent years. Complex models are designed to improve translation performance, but the added complexity also makes decoding more challenging. In this thesis, we focus on designing exact and approximate algorithms for machine translation decoding. More specifically, we will discuss the decoding problems for phrase-based translation models and bidirectional word alignment.
The techniques explored in this thesis are Lagrangian relaxation and local search. Lagrangian relaxation based algorithms give us exact methods that have formal guarantees while being efficient in practice. We study extensions to Lagrangian relaxation that improve the convergence rate on machine translation decoding problems. The extensions include a tightening technique that adds constraints incrementally, optimality-preserving pruning to manage the search space size and utilizing the bounding properties of Lagrangian relaxation to develop an exact beam search algorithm. In addition to having the potential to improve translation accuracy, exact decoding deepens our understanding of the model that we are using, since it separates model errors from optimization errors.
This leads to the question of designing models that improve the translation quality. We design a syntactic phrase-based model that incorporates a dependency language model to evaluate the fluency level of the target language. By employing local search, an approximate method, to decode this richer model, we discuss the trade-off between the complexity of a model and the decoding efficiency with the model.
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Matijević, Domagoj [Verfasser]. "Geometric optimization and querying : exact & approximate / Domagoj Matijević". 2007. http://d-nb.info/1006566449/34.
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Craiu, Virgil Radu. "Multivalent framework for approximate and exact sampling and resampling /". 2001. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:3006484.
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Chen, Wei-Jihi y 陳韋至. "Exact and Approximate Vibration Analysis of Circular Arches Using SCM". Thesis, 2007. http://ndltd.ncl.edu.tw/handle/37000186441510283838.
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Chen, Hsing-Ta. "Delving Into Dissipative Quantum Dynamics: From Approximate to Numerically Exact Approaches". Thesis, 2016. https://doi.org/10.7916/D8M32WBN.
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In this thesis, I explore dissipative quantum dynamics of several prototypical model systems via various approaches, ranging from approximate to numerically exact schemes. In particular, in the realm of the approximate I explore the accuracy of Padé–resummed master equations and the fewest switches surface hopping (FSSH) algorithm for the spin–boson model, and non-crossing approximations (NCA) for the Anderson–Holstein model. Next, I develop new and exact Monte Carlo approaches and test them on the spin–boson model. I propose well–defined criteria for assessing the accuracy of Padé-resummed quantum master equations, which correctly demarcate the regions of parameter space where the Padé approximation is reliable. I continue the investigation of spin–boson dynamics by benchmark comparisons of the semiclassical FSSH algorithm to exact dynamics over a wide range of parameters. Despite small deviations from golden-rule scaling in the Marcus regime, standard surface hopping algorithm is found to be accurate over a large portion of parameter space. The inclusion of decoherence corrections via the augmented FSSH algorithm improves the accuracy of dynamical behavior compared to exact simulations, but the effects are generally not dramatic for the cases I consider. Next, I introduce new methods for numerically exact real-time simulation based on real-time diagrammatic Quantum Monte Carlo (dQMC) and the inchworm algorithm. These methods optimally recycle Monte Carlo information from earlier times to greatly suppress the dynamical sign problem. In the context of the spin–boson model, I formulate the inchworm expansion in two distinct ways: the first with respect to an expansion in the system–bath coupling and the second as an expansion in the diabatic coupling. In addition, a cumulant version of the inchworm Monte Carlo method is motivated by the latter expansion, which allows for further suppression of the growth of the sign error. I provide a comprehensive comparison of the performance of the inchworm Monte Carlo algorithms to other exact methodologies as well as a discussion of the relative advantages and disadvantages of each. Finally, I investigate the dynamical interplay between the electron–electron interaction and the electron–phonon coupling within the Anderson–Holstein model via two complementary NCAs: the first is constructed around the weak-coupling limit and the second around the polaron limit. The influence of phonons on spectral and transport properties is explored in equilibrium, for non-equilibrium steady state and for transient dynamics after a quench. I find the two NCAs disagree in nontrivial ways, indicating that more reliable approaches to the problem are needed. The complementary frameworks used here pave the way for numerically exact methods based on inchworm dQMC algorithms capable of treating open systems simultaneously coupled to multiple fermionic and bosonic baths.
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Wang, Jui-Lung y 王瑞龍. "Approximate and exact collision detection among polyhedral objects in arbitrary motion". Thesis, 1997. http://ndltd.ncl.edu.tw/handle/00259262476980053467.
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碩士國立台灣工業技術學院
電機工程技術研究所
85
This thesis presents the algorithms for collision detection in a 3-Dgraphical environment simulated by a computer system, where all the objectsare represented as polyhedral ones and perform arbitrary translating and/orrotating motions. These algorithms can be directly used for both convex andconcave objects which consist of convex polygons. In the realisticapplications, there require two kinds of solutions: time-interrupted andtime- continuous collision detection; the former can detect the exact positionof a collision event at a fixed time step, and the latter can determine bothapproximate time and position of a collision event. The algorithms first localize the object-to- object collision events by the"space cell" method which divides the 3-D environment into small cells. Inthis manner, only those cells that intersect moving objects are examined inorder to reduce the number of testing a pair of bounding volumes surroundingthe objects. An azimuth-elevation map method is then proposed to quicklyselect the polygons in the overlap region between two candidate objects bypresorting their vertices in the spherical coordinates system. Afterperforming that, a divide- and-conquer method which takes advantage of thebounding box representation is presented to moderate the number of thepolygons needed to be checked by a polygon-to-polygon intersection test. Todeal with the time-interrupted and time- continuous collision detection, twopolygon-to-polygon intersection testing methods based on a hierarchicalscheme are developed to reduce unnecessary computation. All the experiments are made by using the Microsoft Visual C/C++ 4.0compiler under the operation system Microsoft Windows NT 4.0 of a personalcomputer with a Pentium Pro-180 CPU and 64M RAM. As shown in the experiments,the time complexity of the space cell method grows near linearly as theamount of objects increases. When the bounding sphere of an object exactlyembraces its occupied space, the azimuth-elevation map method is moreefficient than the enumerative method for selecting all the polygons withinor across the overlap region. The divide-and- conquer method can economizelots of computing time as the experiments reveal. The time-continuouscollision detection algorithm is successfully verified, and also compared withthe time-interrupted collision detection one to understand its computationloading. So far, all the experimental results from our proposed methods arevery encouraging.
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Wang, Ren-Her y 王仁和. "Approximate and exact D-optimal designs for multiresponse polynomial regression models". Thesis, 2000. http://ndltd.ncl.edu.tw/handle/63391587914649949411.
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碩士國立中山大學
應用數學系研究所
88
The D-optimal design problems in polynomial regression models with a one-dimensional control variable and k-dimensional response variable Y=(Y_1,...,Y_k) where there are some common unknown parameters are discussed. The approximate D-optimal designs are shown to be independent of the covariance structure between the k responses when the degrees of the k responses are of the same order. Then, the exact n-point D-optimal designs are also discussed. Krafft and Schaefer (1992) and Imhof (2000) are useful in obtaining our results. We extend the proof of symmetric cases for k>= 2.
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Liu, Peter (Ying-Chun) y 劉寅春. "Exact and Approximate LMI-Based Control for Fuzzy and Nonlinear Systems". Thesis, 2002. http://ndltd.ncl.edu.tw/handle/75833823056105100651.
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Pearson, James Ross. "Exact, Approximate, and Online Algorithms for Optimization Problems Arising in DVD Assignment". Thesis, 2009. http://hdl.handle.net/10012/4666.
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Zip.ca is an online DVD rental company that faces two major operational problems:
calculation of the assignment of DVDs to customers every thirty minutes
throughout the day and purchasing of new inventory in regular intervals.
In this thesis, we model these two problems and develop algorithms to solve
them. In doing so, we encounter many theoretical problems that are both applicable
to Zip’s operations and intrinsically interesting problems independent of the
application.
First, we note that the assignment problem facing Zip is inherently in an online
setting. With returns of DVDs being processed throughout the day, the dataset
is constantly changing. Although the ideal solution would be to wait until the
end of the day to make decisions, physical work load capacities prevent this. For
this reason we discuss two online problems, online 0-1 budgeted matching and
the budgeted Adwords auction. We present a 1/(2 w_max/w_min)-competitive algorithm for the online 0-1 budgeted matching problem, and prove that this is the best possible
competitive ratio possible for a wide class of algorithms. We also give a (1− (S+1)/(S+e) )-competitive algorithm for the budgeted Adwords auction as the size of the bids
and cost get small compared to the budgets, where S is the ratio of the highest and
lowest ratios of bids to costs.
We suggest a linear programming approach to solve Zip’s assignment problem.
We develop an integer program that models the B-matching instance with additional
constraints of concern to Zip, and prove that this integer program belongs to
a larger class of integer programs that has totally unimodular constraint matrices.
Thus, the assignment problem can be solved to optimality every thirty minutes.
We additionally create a test environment to check daily performance, and provide
real-time implementation results, showing a marked improvement over Zip’s old
algorithm.
We show that Zip’s purchasing problem can be modeled by the matching augmentation
problem defined as follows. Given a graph with vertex capacities and
costs, edge weights, and budget C, find a purchasing of additional node capacity of
cost at most C that admits a B-matching of maximum weight. We give a PTAS for
this problem, and then present a special case that is polynomial time solvable that
still models Zip’s purchasing problem, under the assumption of uniform costs.
We then extend the augmentation idea to matroids and present matroid augmentation,
matroid knapsack, and matroid intersection knapsack, three NP-hard
problems. We give an FPTAS for matroid knapsack by dynamic programming,
PTASes for the other two, and demonstrate applications of these problems.
33
Olaechea, Velazco Rafael Ernesto. "Comparison of Exact and Approximate Multi-Objective Optimization for Software Product Lines". Thesis, 2013. http://hdl.handle.net/10012/8015.
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Software product lines (SPLs) manage product variants in a systematical way and allow stakeholders to derive variants by selecting features. Finding a desirable variant is hard, due to the huge configuration space and usually conflicting objectives (e.g., lower cost and higher performance). This scenario can be reduced to a multi-objective optimization prob- lem in SPLs. We address the problem using an exact and an approximate algorithm and compare their accuracy, time consumption, scalability and parameter setting requirements on five case studies with increasing complexity.
Our empirical results show that (1) it is feasible to use exact techniques for small SPL multi-objective optimization problems, and (2) approximate methods can be used for large problems but require substantial effort to find the best parameter settings for acceptable approximation. Finally, we discuss the tradeoff between accuracy and time consumption when using exact and approximate techniques for SPL multi-objective optimization and guide stakeholders to choose one or the other in practice.
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Luo, Youh Wen y 羅毓文. "Exact and Approximate Approaches for the Vehicle Routing Problem with Packing Constraints". Thesis, 1995. http://ndltd.ncl.edu.tw/handle/31673209223814430399.
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Hsieh, Hsiu-Ching y 謝秀青. "False-overlap tiles elimination for tile-based rendering: exact and approximate methods". Thesis, 2009. http://ndltd.ncl.edu.tw/handle/48928573954114759004.
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碩士國立交通大學
多媒體工程研究所
97
In graphics processing, overlap test is a crucial step before tile-binning in tile-based rendering for embedded devices. An object in a frame is decomposed into primitives, triangles of different sizes, for processing. In tile-binning process, these triangular primitives are typically represented by bounding boxes. However, the bounding box of a primitive usually covers a significant number of tiles which are not overlapped by the primitive. These tiles are called false-overlap tiles and approximate 70% of the tiles of a bounding box. Therefore, in tile-based rendering, identifying and eliminating those false-overlap tiles in a bounding box to reduce both storage pressures in tile-binning and data accesses of external memory for rasterizer become inviting. Existing false-overlap detection algorithms are either too tedious to reduce computation or too rough to gain high coverage. In this paper, we propose three methods to eliminate all false-overlap tiles: Cross-Product Test (CPT), Edge-Walk Test (EWT), Counting X-Ratio (CXR) and approximation method. We partition the bounding box of a primitive into three rectangles at most according to the number of primitive vertices which are also the vertices of the bounding box. The edges of the primitive then become the diagonals of these rectangles, and false overlap detection becomes a well-formulated math processing. The false-overlap detection of these three rectangles may be processed in parallel to improve performance further. The proposed methods are tested using Doom3 and Quake4 for different screen sizes.
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Soroush, Milad. "Accuracies of Optimal Transmission Switching Heuristics Based on Exact and Approximate Power Flow Equations". Thesis, 2013. http://hdl.handle.net/10012/7584.
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Optimal transmission switching (OTS) enables us to remove selected transmission lines from service as a cost reduction method. A mixed integer programming (MIP) model has been proposed to solve the OTS problem based on the direct current optimal power flow (DCOPF) approximation. Previous studies indicated computational issues regarding the OTS problem and the need for a more accurate model. In order to resolve computational issues, especially in large real systems, the MIP model has been followed by some heuristics to find good, near optimal, solutions in a reasonable time. The line removal recommendations based on DCOPF approximations may result in poor choices to remove from service. We assess the quality of line removal recommendations that rely on DCOPF-based heuristics, by estimating actual cost reduction with the exact alternating current optimal power flow (ACOPF) model, using the IEEE 118-bus test system. We also define an ACOPF-based line-ranking procedure and compare the quality of its recommendations to those of a previously published DCOPF-based procedure. For the 118-bus system, the DCOPF-based line ranking produces poor quality results, especially when demand and congestion are very high, while the ACOPF-based heuristic produces very good quality recommendations for line removals, at the expense of much longer computation times. There is a need for approximations to the ACOPF that are accurate enough to produce good results for OTS heuristics, but fast enough for practical use for OTS decisions.
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Pan, Z. H. y 潘子豪. "An Approximate String Matching Based on an Exact String Matching with Constant Pattern Length". Thesis, 2008. http://ndltd.ncl.edu.tw/handle/45738203365580501083.
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碩士國立暨南國際大學
資訊工程學系
96
The string matching problem is a very important problem which is needed to solve in computer science, computational biology and other domains. The exact matching problem is defined as follows: Given a string T whose length is n and a string P whose length is m, n≧m, find each location where string P occurs in string T. The approximate string matching problem is defined as follows: Given a pattern string P of length and a text string T of length n, n≧m, and a maximal number k of errors allowed, find each location i of T such that there exists a suffix T of T(0,i) and ED(A,B)≦k. In our thesis, we will use the exact string matching to solve the approximate string matching problem.
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Pan, Zu-Hao. "An Approximate String Matching Based on an Exact String Matching with Constant Pattern Length". 2008. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0020-2406200816061900.
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Hesse, Derek H. "Practical applicability of exact and approximate forms of the randomization test for two independent samples". Thesis, 1987. http://hdl.handle.net/10945/22424.
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Eigenwillig, Arno [Verfasser]. "Real root isolation for exact and approximate polynomials using Descartes' rule of signs / vorgelegt von Arno Eigenwillig". 2008. http://d-nb.info/1005305412/34.
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Schnalle, Roman. "Symmetry assisted exact and approximate determination of the energy spectra of magnetic molecules using irreducible tensor operators". Doctoral thesis, 2009. https://repositorium.ub.uni-osnabrueck.de/handle/urn:nbn:de:gbv:700-2009102618.
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In this work a numerical approach for the determination of the energy spectra and the calculation of thermodynamic properties of magnetic molecules is presented. The work is focused on the treatment of spin systems which exhibit point-group symmetries. Ring-like and archimedean-type structures are discussed as prominent examples. In each case the underlying spin quantum system is modeled by an isotropic Heisenberg Hamiltonian. Its energy spectrum is calculated either by numerical exact diagonalization or by an approximate diagonalization method introduced here. In order to implement full spin-rotational symmetry the numerical approach at hand is based on the use of irreducible tensor operators. Furthermore, it is shown how an unrestricted use of point-group symmetries in combination with the use of irreducible tensor operators leads to a reduction of the dimensionalities as well as to additional information about the physics of the systems. By exemplarily demonstrating how the theoretical foundations of the irreducible tensor operator technique can be realized within small spin systems the technical aspect of this work is covered. These considerations form the basis of the computational realization that was implemented and used in order to get insight into the investigated systems.
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Rising, William Randolph. "Exponential chains and generalized inverses: New approaches to the approximate and exact solution of Markov chain problems". 1989. https://scholarworks.umass.edu/dissertations/AAI8917393.
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Markov chains are considered with emphasis on the compution of exact and approximate stationary distributions and expected first passage times. First, generalized inverses are used to unify the computations involved with Markov chains. It is shown that any generalized inverse of the infinitesimal generator of a Markov chain can be used to find the exact stationary distribution and expected first passage times, as well as to compute the effects on these quantities by a perturbation of the infinitesimal generator. Next, because of the use in the literature of birth-death chains in various forms as approximations to chains which have been loosely termed nearly birth-death chains, there is a discussion of what might be a useful definition of a nearly birth-death chain. The experimental results of birth-death approximations of some chains arising from the slotted ALOHA are then presented. These lend some validity to approximating such chains with birth-death chains which match the local drift and variance at each internal state. The discussion of nearly birth-death chains leads to the discovery of a new class of chains, called exponential chains, which generalizes the birth-death chain by introducing two parameters in addition to the birth-death rates. Explicit formulae for the stationary distribution and expected first passage times are computed, and seen to be similar to those used for birth-death chains. It is pointed out that the computational ease and the additional two parameters could make exponential chains better for approximating Markov chains. An example is given where the exponential chains yield good approximations. Finally, exponential chains are used to improve bounds on the ratios of stationary probabilities of adjacent states which were originally developed by Szpankowski. The improvements are in the form of an existence theorem, and a possible first step for the computation of the improved bounds is given.
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Janovit-Freireich, Itnuit. "Computation of the exact and approximate radicals of ideals techniques based on matrices of traces, moment matrices and bezoutians /". 2008. http://www.lib.ncsu.edu/theses/available/etd-06032008-105538/unrestricted/etd.pdf.
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Schnalle, Roman [Verfasser]. "Symmetry assisted exact and approximate determination of the energy spectra of magnetic molecules using irreducible tensor operators / vorgelegt von Roman Schnalle". 2009. http://d-nb.info/99767539X/34.
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