On the complexity of the multiple stack TSP, kSTSP

The multiple Stack Travelling Salesman Problem, STSP, deals with the collect and the deliverance of n commodities in two distinct cities. The two cities are represented by means of two edge-valued graphs (G1,d2) and (G2,d2). During the pick-up tour, the commodities are stored into a container whose rows are subject to LIFO constraints. As a generalisation of standard TSP, the problem obviously is NP-hard; nevertheless, one could wonder about what combinatorial structure of STSP does the most impact its complexity: the arrangement of the commodities into the container, or the tours themselves? The answer is not clear. First, given a pair (T1,T2) of pick-up and delivery tours, it is polynomial to decide whether these tours are or not compatible. Second, for a given arrangement of the commodities into the k rows of the container, the optimum pick-up and delivery tours w.r.t. this arrangement can be computed within a time that is polynomial in n, but exponential in k. Finally, we provide instances on which a tour that is optimum for one of three distances d1, d2 or d1+d2 lead to solutions of STSP that are arbitrarily far to the optimum STSP

Approximability of the Multiple Stack TSP

STSP seeks a pair of pickup and delivery tours in two distinct networks, where the two tours are related by LIFO contraints. We address here the problem approximability. We notably establish that asymmetric MaxSTSP and MinSTSP12 are APX, and propose a heuristic that yields to a 1/2, 3/4 and 3/2 standard approximation for respectively Max2STSP, Max2STSP12 and Min2STSP12

Problèmes de tournées de véhicules avec contraintes de chargement

Cette thèse s’intéresse aux problèmes de tournées de véhicules où l’on retrouve des contraintes de chargement ayant un impact sur les séquences de livraisons permises. Plus particulièrement, les items placés dans l’espace de chargement d’un véhicule doivent être directement accessibles lors de leur livraison sans qu’il soit nécessaire de déplacer d’autres items. Ces problèmes sont rencontrés dans plusieurs entreprises de transport qui livrent de gros objets (meubles, électroménagers). Le premier article de cette thèse porte sur une méthode exacte pour un problème de confection d’une seule tournée où un véhicule, dont l’aire de chargement est divisée en un certain nombre de piles, doit effectuer des cueillettes et des livraisons respectant une contrainte de type dernier entré, premier sorti. Lors d’une collecte, les items recueillis doivent nécessairement être déposés sur le dessus de l’une des piles. Par ailleurs, lors d’une livraison, les items doivent nécessairement se trouver sur le dessus de l’une des piles. Une méthode de séparation et évaluation avec plans sécants est proposée pour résoudre ce problème. Le second article présente une méthode de résolution exacte, également de type séparation et évaluation avec plans sécants, pour un problème de tournées de véhicules avec chargement d’items rectangulaires en deux dimensions. L’aire de chargement des véhicules correspond aussi à un espace rectangulaire avec une orientation, puisque les items doivent être chargés et déchargés par l’un des côtés. Une contrainte impose que les items d’un client soient directement accessibles au moment de leur livraison. Le dernier article aborde une problème de tournées de véhicules avec chargement d’items rectangulaires, mais où les dimensions de certains items ne sont pas connus avec certitude lors de la planification des tournées. Il est toutefois possible d’associer une distribution de probabilités discrète sur les dimensions possibles de ces items. Le problème est résolu de manière exacte avec la méthode L-Shape en nombres entiers.In this thesis, we study mixed vehicle routing and loading problems where a constraint is imposed on delivery sequences. More precisely, the items in the loading area of a vehicle must be directly accessible, without moving any other item, at delivery time. These problems are often found in the transportation of large objects (furniture, appliances). The first paper proposes a branch-and-cut algorithm for a variant of the single vehicle pickup and delivery problem, where the loading area of the vehicle is divided into several stacks. When an item is picked up, it must be placed on the top of one of these stacks. Conversely, an item must be on the top of one of these stacks to be delivered. This requirement is called “Last In First Out” or LIFO constraint. The second paper presents another branch-and-cut algorithm for a vehicle routing and loading problem with two-dimensional rectangular items. The loading area of the vehicles is also a rectangular area where the items are taken out from one side. A constraint states that the items of a given customer must be directly accessible at delivery time. The last paper considers a stochastic vehicle routing and loading problem with two- dimensional rectangular items where the dimensions of some items are unknown when the routes are planned. However, it is possible to associate a discrete probability distribution on the dimensions of these items. The problem is solved with the Integer L-Shaped method

Optimization for Decision Making II

In the current context of the electronic governance of society, both administrations and citizens are demanding the greater participation of all the actors involved in the decision-making process relative to the governance of society. This book presents collective works published in the recent Special Issue (SI) entitled “Optimization for Decision Making II”. These works give an appropriate response to the new challenges raised, the decision-making process can be done by applying different methods and tools, as well as using different objectives. In real-life problems, the formulation of decision-making problems and the application of optimization techniques to support decisions are particularly complex and a wide range of optimization techniques and methodologies are used to minimize risks, improve quality in making decisions or, in general, to solve problems. In addition, a sensitivity or robustness analysis should be done to validate/analyze the influence of uncertainty regarding decision-making. This book brings together a collection of inter-/multi-disciplinary works applied to the optimization of decision making in a coherent manner

Comunidades Inteligentes para la Construcción y Gestión de Arquitecturas Optimizadas de de Sistemas Multiagente

[ES] El desarrollo de sistemas informáticos es una labor más o menos costosa en función de su complejidad. El hecho de poder reutilizar, parcial o totalmente, trozos de un sistema para otros desarrollos, implica una reducción en el tiempo empleado, una mayor facilidad de implementación y evita la redundancia de funcionalidades. Este planteamiento llevado a los sistemas multiagente ha de tener en cuenta las características propias de los agentes, para lo cual se requiere que la reutilización pueda llevarse a cabo a partir de pequeños subsistemas de agentes especializados con una organización establecida. Además, para explotar la capacidad de estos pequeños subsistemas de agentes es necesaria una arquitectura que tenga como finalidad la coordinación de los mismos, y que de forma modular y escalada, pueda desarrollarse para lograr objetivos de mayor complejidad. A lo largo de este trabajo se llevará a cabo un estudio de las características de los agentes y sistemas multiagente, asi como de las organizaciones humanas y su implementación a partir de las organizaciones virtuales, destacando su importancia y efectividad en el desarrollo actual de sistemas multiagente. Llegado este punto se realizará el diseño de SCODA (Distributed and Specialized Agent COmmunities), una nueva arquitectura modular para el desarrollo de sistemas multiagente. Mediante SCODA se permite el desarrollo de sistemas multiagente bajo una filosofía modular especializada, a través de la cual las funcionalidades del sistema puedan ir ampliándose, de forma escalada, en función de las necesidades. SCODA se compone de pequeños subsistemas de agentes, denominados Comunidades Inteligentes Especializadas (CIE), los cuales proveen las funcionalidades necesarias para resolver las necesidades requeridas a través de servicios distribuidos. Mediante estas CIE se permite una escalabilidad de los sistemas de forma que puedan ser reutilizadas en diferentes desarrollos, independientemente de su finalidad. La validación de esta arquitectura se realizará a partir de un caso de estudio centrado en tareas principalmente logísticas, debido a la variedad de situaciones que pueden darse en este tipo de ambientes. A partir de este caso de estudio se analizará y evaluará el comportamiento de la arquitectura y podrá llevarse a cabo su validaciónComputers systems development is more or less difficult task according to its complexity. The fact of being able to re-use, partially or completely, pieces of a system for other developments, involves a time reduction, a major implementation facility and avoids the functionalities redundancy. This aim applied to multiagent systems has to bear in mind the own characteristics of the agents, for which it is needed that the re-using could be carried out from small subsystems of specialized agents with an established organization. Also, to improve the capacity of these small subsystems of agents, is necessary an architecture, that has the objective to take the coordination of the same ones, and in a modular and scalable way, could develop to achieve aims with a major complexity. Throughout this work will be carried out a study of the characteristics of the agents and multiagent systems, as well as of human organizations and its deployment on virtual organizations, highlighting its importance and effectiveness in the current development of multiagent systems. From here it will be developed the design of SCODA (Distributed and Specialized Agent Communities), a new modular architecture for the development of multiagent systems. By means of SCODA, is allowed that multiagent systems could be developed from a specialized modular philosophy, across it the functionalities of the system can be extended in scaled form according to the objectives. SCODA is composed by small subsystems of agents named, Specialized Intelligent Communities (SCI), which provide the necessary functionalities to solve the objectives needed across distributed services. By means of these CIE, scalability of the systems is allowed, so that they could be re-used in different developments, independently of his purpose. SCODA is integrated by smaller subsystems of agents, called Intelligent Communities Specialized (SCI), which provide the functionality necessary to resolve the aims, using distributed services. These SCI allow a scalability of the systems so that can be reused in different developments, regardless of its purpose. The validation of this architecture will be realized through a case of study, focused on logistical tasks mainly due to the variety of situations that may arise in this kind of environments. From this case of study, we will analyze and assess the behaviour of the architecture and will carry out its validation