Un algoritmo multithreading para el problema del árbol de Steiner

Este artículo presenta una implementación paralela de la metaheurística SN [13] utilizando una técnica de programación multithreading y su aplicación a la resolución del problema del árbol de Steiner. Se describen las decisiones de diseño del algoritmo y se presentan experimentos realizados sobre un conjunto de problemas de prueba estándar, analizando la calidad de resultados obtenidos y la eficiencia computacional de la versión paralela del algoritmo.Eje: IV - Workshop de procesamiento distribuido y paraleloRed de Universidades con Carreras en Informática (RedUNCI

Un algoritmo multithreading para el problema del árbol de Steiner

Este artículo presenta una implementación paralela de la metaheurística SN [13] utilizando una técnica de programación multithreading y su aplicación a la resolución del problema del árbol de Steiner. Se describen las decisiones de diseño del algoritmo y se presentan experimentos realizados sobre un conjunto de problemas de prueba estándar, analizando la calidad de resultados obtenidos y la eficiencia computacional de la versión paralela del algoritmo.Eje: IV - Workshop de procesamiento distribuido y paraleloRed de Universidades con Carreras en Informática (RedUNCI

Ant Colony Optimization for Multi-objective Digital Convergent Product Network

Convergent product is an assembly shape concept integrating functions and sub-functions to form a final product. To conceptualize the convergent product problem, a web-based network is considered in which a collection of base functions and sub-functions configure the nodes and each arc in the network is considered to be a link between two nodes. The aim is to find an optimal tree of functionalities in the network adding value to the product in the web environment. First, an algorithm is proposed to assign the links among bases and sub-functions. Then, numerical values as benefits and costs are determined for arcs and nodes, respectively, using a mathematical approach. Also, customer’s value corresponding to the benefits is considered. Finally, the Steiner tree methodology is adapted to a multi-objective model optimized by an ant colony optimization method. The approach is applicable for all digital products, such as mobile, tablet, laptop, etc. An example is worked out to illustrate the proposed approach

Optimisation de la conception d'un réseau de collecte d’énergie éolienne par recherche locale

RÉSUMÉ : Le problème de l'optimisation de la conception de réseaux, plus particulièrement d'un parc éolien, intervient lorsqu'une compagnie souhaite louer une partie des câbles de transmission d'un réseau appartenant à un tiers parti (l'État ou une autre compagnie) et construire/acheter l'autre partie manquante. Il est possible de reformuler ce problème comme le problème de l'arbre de Steiner en adaptant la fonction de coût des câbles de transmission. Une fois cette adaptation faite, une heuristique employant une méthode exacte est développée. L'heuristique développée se découpe en deux pans : 1) la construction d'une solution réalisable initiale itérativement en utilisant un algorithme de plus court chemin, et 2) l'amélioration de cette solution par une série de déconnexions de certaines parties de la solution et de leur reconnexion à l'autre partie restante non déconnectée de la solution en question. Les résultats montrent que la méthode de construction de la solution initiale échoue parfois à trouver une solution réalisable. Ils montrent également que pour de larges exemplaires, le prototype d'amélioration de la solution initiale s'avère très efficace et pourra vraisemblablement s'attaquer à de très gros problèmes, impensables à résoudre avec les méthodes actuelles, si quelques ajustements sont faits.----------ABSTRACT : The problem of optimizing the design of network, in particular wind farm network, occurs when a company wishes to rent cables from a part of an existing transmission network owned by a third party (the government or another company) and construct or buy cables from the other part missing. It is possible to reformulate this problem as the Steiner tree problem in graph by adjusting the cost function of the transmission cables. Once this adaptation made, a heuristic using an exact method is developed. The heuristic developed is divided into two sections: 1) the construction of an initial feasible solution iteratively using the shortest path algorithm, and 2) improving this solution by a series of disconnection of parts of the solution and their connection to the other remaining portion not disconnected from the solution at hand. The results show that the method of construction of the initial solution sometimes fails to find a feasible solution. They also show that for large instances, the heuristic is very effective and will probably find good solutions also for very large problems, unthinkable to solve with current methods, if some adjustments are made

Design of power efficient multicast algorithms for sparse split WDM networks

Recent years witnessed tremendous increase in data traffic as new Internet applications were launched. Optical networks employing recent technologies such as DWDM and EDFA`s emerged as the most prominent and most promising solutions in terms of their ability to keep with the demand on bandwidth. However for a class of applications bandwidth is not the only important requirement, These applications require efficient multicast operations. They include data bases, audio/video conferencing, distributed computing etc. Multicasting in the optical domain however has its own unique set of problems. First, an optical signal can be split among the outputs of a node but the power due to splitting can be significantly reduced. Second, the hardware for split nodes is relatively expensive and therefore we cannot afford to employ it at every node. Third, there are other sources of losses such as attenuation losses and multiplexing /de-multiplexing losses. This thesis deals with the important issue of Power Efficient multicast in WDM optical networks. We report three new algorithms for constructing power efficient multicast trees and forests. Our algorithms are the first to take into account all possible sources of power losses while constructing the trees. We utilize the techniques of backtracking and tree pruning judiciously to achieve very power efficient multicast trees. The first two algorithms use modified versions of the shortest path heuristic to build the tree. The third algorithm however, uses a novel concept and considers power at every tree building step. In this algorithm, the order of inclusion of destination nodes into the tree is based on the power distribution in the tree and not distance. All three algorithms prune the trees if the power levels at the destinations are not acceptable. The performance of these three algorithms under several constraints is studied on several irregular topologies. All three algorithms reported in this work produce significant improvements in signal strength at the set of destinations over the existing multicast algorithms. Numerical results show that our third algorithm outperforms the first two algorithms as well as the existing multicasting algorithms

Trusted content-based publish/subscribe trees

Publish/Subscribe systems hold strong assumptions of the expected behaviour of clients and routers, as it is assumed they all abide by the matching and routing protocols. Assumptions of implicit trust between the components of the publish/subscribe infrastructure are acceptable where the underlying event distribution service is under the control of a single or multiple co-operating administrative entities and contracts between clients and these authorities exist, however there are application contexts where these presumptions do not hold. In such environments, such as ad hoc networks, there is the possibility of selfish and malicious behaviour that can lead to disruption of the routing and matching algorithms. The most commonly researched approach to security in publish/subscribe systems is role-based access control (RBAC). RBAC is suitable for ensuring confidentiality, but due to the assumption of strong identities associated with well defined roles and the absence of monitoring systems to allow for adaptable policies in response to the changing behaviour of clients, it is not appropriate for environments where: identities can not be assigned to roles in the absence of a trusted administrative entity; long-lived identities of entities do not exist; and where the threat model consists of highly adaptable malicious and selfish entities. Motivated by recent work in the application of trust and reputation to Peer-to-Peer networks, where past behaviour is used to generate trust opinions that inform future transactions, we propose an approach where the publish/subscribe infrastructure is constructed and re-configured with respect to the trust preferences of clients and routers. In this thesis, we show how Publish/Subscribe trees (PSTs) can be constructed with respect to the trust preferences of publishers and subscribers, and the overhead costs of event dissemination. Using social welfare theory, it is shown that individual trust preferences over clients and routers, which are informed by a variety of trust sources, can be aggregated to give a social preference over the set of feasible PSTs. By combining this and the existing work on PST overheads, the Maximum Trust PST with Overhead Budget problem is defined and is shown to be in NP-complete. An exhaustive search algorithm is proposed that is shown to be suitable only for very small problem sizes. To improve scalability, a faster tabu search algorithm is presented, which is shown to scale to larger problem instances and gives good approximations of the optimal solutions. The research contributions of this work are: the use of social welfare theory to provide a mechanism to establish the trustworthiness of PSTs; the finding that individual trust is not interpersonal comparable as is considered to be the case in much of the trust literature; the Maximum Trust PST with Overhead Budget problem; and algorithms to solve this problem

MODELING AND OPTIMIZATION OF TRANSMISSION NETWORKS

This dissertation focuses on transmission networks. These networks play an important role in communication (including data and voice), energy transmission (such as gas, electrical, and oil), and micro-electronics among other areas. In this dissertation, we consider two different problems associated with transmission networks: the dynamics on a data communication network and the optimal design of a general transmission network located on a non-uniform landscape. The first two parts of this dissertation develop and apply mathematical models of congested Internet connections and describe possible extensions to network traffic state estimation and network security. The third part looks at an optimal network design problem through a variation on the Euclidean Steiner tree problem, a well-known network optimization problem

Conception et optimisation d'un système de collecte d'énergie éolienne

Resumé : Cette thèse porte sur l'étude du problème de conception d'un réseau de collecte d'énergie éolienne. Celui-ci consiste à installer les capacités sur les liens d'un réseau électrique potentiel pour acheminer au moindre coût l'énergie produite par des éoliennes vers une sous-station de transformation. L'augmentation du nombre d'éoliennes installées dans un parc éolien nécessite la conception des réseaux étendus sur plusieurs kilomètres de lignes électriques et donc des investissements importants. Face à un tel enjeu financier, l'utilisation d'outils d'optimisation de conception de réseaux s'avère capitale. Le problème de conception d'un réseau de collecte d'énergie éolienne fait partie d'une grande classe de problèmes de conception de réseaux. Mise à part sa complexité héritée de cette classe, ce dernier est sujet à une contrainte technique importante à savoir la non-bifurcation de l'énergie. En effet, les concepteurs de réseau exigent que l'énergie produite par un groupe d'éoliennes et qui est combinée sur un lien donné reste combinée jusqu'à ce qu'elle atteigne la sous-station. Dans cette thèse, nous nous sommes concentrés sur deux variantes de ce problème. La première variante consiste à installer des câbles souterrains et des lignes de transmission sur les liens potentiels du réseau électrique tels qu'un seul choix de capacité est disponible. La deuxième variante qui est plus compliquée que la première consiste non seulement à déterminer les liens qui sont utilisés pour acheminer l'énergie vers la sous-station, mais également à choisir la capacité de chaque lien utilisé, ce choix devant être fait parmi un ensemble de possibilités fixé par les concepteurs. Tous ces choix doivent être faits en prenant en considération les pertes engendrées par le transfert de l'énergie dans ce réseau. Dans les deux variantes, nous supposons que l'emplacement des éoliennes est prédéfini et qu'il est possible d'installer plusieurs liens parallèles entre deux sommets du réseau. Face à la complexité de ce problème, nous proposons des approches exactes pour la résolution des deux variantes. Plus précisément, nous commençons d'abord par développer les formulations mathématiques appropriées. Nous nous orientons ensuite vers les techniques basées sur la théorie polyédrale qui, de nos jours, sont qualifiées comme très efficaces pour la résolution de problèmes complexes en optimisation combinatoire. Nous déterminons en particulier des inégalités valides et proposons des techniques pour la génération de plans coupants. Toutes les méthodes proposées sont testées sur des exemplaires concrets fournis par notre partenaire industriel. ---------- Abstract : The aim of this thesis is to study the wind farm collection network design problem which consists of choosing a subset of edges of a potential electrical network and assigning the right capacity to each link so that the energy produced by the wind turbines can be sent to a specific sub-station at minimum cost. Designing such an electrical network incures a significant cost when building a wind farm. Therefore, it will be useful to develop efficient tools to find an optimal design in reasonable computation time. The wind farm collection network design problem belongs to a large class of network design problems which is known to be $NP$-hard. In designing a collection network, one must take an important engineering constraint into account. The energy flowing through a link is unsplittable, i.e., once the energy units produced by wind turbines and bundled on a given link these units have to remain bundled until they reach the substation. In this thesis, we will focus on two versions of this problem. The first one consists of selecting edges to install underground cables and transmission lines such that there is only one capacity for each type of link (cable or transmission line). In the second version of the problem we are allowed to install different types of capacities on the edges of the electrical network. Furthermore, power losses due to energy dissipation are accounted for when calculating the objective function. We assume that the locations of the turbines are already known for the two versions of the problem and several parallel links may be installed between two endpoints. We propose models and algorithms for the two versions of the problem. Then we discuss several ways to strengthen our models by means of valid inequalities. We also develop procedures for generating cutting planes. Computational tests performed on instances provided by our industrial partner confirm the efficiency of the proposed methods

Algoritmos genéticos paralelos y su aplicación al diseño de redes de comunicaciones confiables

Esta Tesis presenta el estudio de las técnicas de computación evolutiva y la aplicación de técnicas de procesamiento de alta performance para implementar modelos de algoritmos genéticos capaces de ejecutar en un ambiente paralelo distribuido. Se aborda la aplicación de algoritmos evolutivos al caso concreto de problemas que surgen al diseñar redes de comunicaciones de alta conectividad topológica. En particular, se concentró el estudio sobre una clase de problemas de diseño de redes de comunicaciones que pueden modelarse bajo el denominado Problema de Steiner Generalizado. Dada una red de comunicaciones con ciertos nodos distinguidos denominados nodos terminales, el Problema de Steiner Generalizado propone diseñar una subred de mínimo costo que verifique un conjunto de requisitos prefijados de conectividad entre pares de nodos terminales. En el trabajo se evalúan diferentes algoritmos evolutivos puros e híbridos en sus versiones secuenciales y paralelas, presentando un estudio comparativo que reporta resultados satisfactorios tanto desde el punto de vista de la calidad de resultados obtenidos como desde el punto de vista de la mejora de eficiencia computacional alcanzada por las versiones paralelas de los algoritmos con respecto a sus contrapartes secuenciales