An Effective Metaheuristic for Multiple Traveling Repairman Problem with Distance Constraints

Multiple Traveling Repairman Problem with Distance Constraints (MTRPD) is an extension of the NP-hard Multiple Traveling Repairman Problem. In MTRPD, a fleet of identical vehicles is dispatched to serve a set of customers with the following constraints. First, each vehicle's travel distance is limited by a threshold. Second, each customer must be visited exactly once. Our goal is to find the visiting order that minimizes the sum of waiting times. To solve MTRPD we propose to combine the Insertion Heuristic (IH), Variable Neighborhood Search (VNS), and Tabu Search (TS) algorithms into an effective two-phase metaheuristic that includes a construction phase and an improvement phase. In the former phase, IH is used to create an initial solution. In the latter phase, we use VNS to generate various neighborhoods, while TS is employed to mainly prohibit from getting trapped into cycles. By doing so, our algorithm can support the search to escape local optima. In addition, we introduce a novel neighborhoods’ structure and a constant time operation which are efficient for calculating the cost of each neighboring solution. To show the efficiency of our proposed metaheuristic algorithm, we extensively experiment on benchmark instances. The results show that our algorithm can find the optimal solutions for all instances with up to 50 vertices in a fraction of seconds. Moreover, for instances from 60 to 80 vertices, almost all found solutions fall into the range of 0.9 %-1.1 % of the optimal solutions' lower bounds in a reasonable duration. For instances with a larger number of vertices, the algorithm reaches good-quality solutions fast. Moreover, in a comparison to the state-of-the-art metaheuristics, our proposed algorithm can find better solutions

The Multi-Depot Minimum Latency Problem with Inter-Depot Routes

The Minimum Latency Problem (MLP) is a class of routing problems that seeks to minimize the wait times (latencies) of a set of customers in a system. Similar to its counterparts in the Traveling Salesman Problem (TSP) and Vehicle Routing Problem (VRP), the MLP is NP-hard. Unlike these other problem classes, however, the MLP is customer-oriented and thus has impactful potential for better serving customers in settings where they are the highest priority. While the VRP is very widely researched and applied to many industry settings to reduce travel times and costs for service-providers, the MLP is a more recent problem and does not have nearly the body of literature supporting it as found in the VRP. However, it is gaining significant attention recently because of its application to such areas as disaster relief logistics, which are a growing problem area in a global context and have potential for meaningful improvements that translate into reduced suffering and saved lives. An effective combination of MLP\u27s and route minimizing objectives can help relief agencies provide aid efficiently and within a manageable cost. To further the body of literature on the MLP and its applications to such settings, a new variant is introduced here called the Multi-Depot Minimum Latency Problem with Inter-Depot Routes (MDMLPI). This problem seeks to minimize the cumulative arrival times at all customers in a system being serviced by multiple vehicles and depots. Vehicles depart from one central depot and have the option of refilling their supply at a number of intermediate depots. While the equivalent problem has been studied using a VRP objective function, this is a new variant of the MLP. As such, a mathematical model is introduced along with several heuristics to provide the first solution approaches to solving it. Two objectives are considered in this work: minimizing latency, or arrival times at each customer, and minimizing weighted latency, which is the product of customer need and arrival time at that customer. The case of weighted latency carries additional significance as it may correspond to a larger number of customers at one location, thus adding emphasis to the speed with which they are serviced. Additionally, a discussion on fairness and application to disaster relief settings is maintained throughout. To reflect this, standard deviation among latencies is also evaluated as a measure of fairness in each of the solution approaches. Two heuristic approaches, as well as a second-phase adjustment to be applied to each, are introduced. The first is based on an auction policy in which customers bid to be the next stop on a vehicle\u27s tour. The second uses a procedure, referred to as an insertion technique, in which customers are inserted one-by-one into a partial routing solution such that each addition minimizes the (weighted) latency impact of that single customer. The second-phase modification takes the initial solutions achieved in the first two heuristics and considers the (weighted) latency impact of repositioning nodes one at a time. This is implemented to remove potential inefficient routing placements from the original solutions that can have compounding effects for all ensuing stops on the tour. Each of these is implemented on ten test instances. A nearest neighbor (greedy) policy and previous solutions to these instances with a VRP objective function are used as benchmarks. Both heuristics perform well in comparison to these benchmarks. Neither heuristic appears to perform clearly better than the other, although the auction policy achieves slightly better averages for the performance measures. When applying the second-phase adjustment, improvements are achieved and lead to even greater reductions in latency and standard deviation for both objectives. The value of these latency reductions is thoroughly demonstrated and a call for further research regarding customer-oriented objectives and evaluation of fairness in routing solutions is discussed. Finally, upon conclusion of the results presented in this work, several promising areas for future work and existing gaps in the literature are highlighted. As the body of literature surrounding the MLP is small yet growing, these areas constitute strong directions with important relevance to Operations Research, Humanitarian Logistics, Production Systems, and more

Problemas de rotas com custos cumulativos em distribuição logística

Mestrado em Controlo de Gestão e dos NegóciosNesta dissertação aborda-se um importante problema de distribuição logística, o problema da determinação de rotas ótimas designadas na literatura da especialidade por Vehicle Routing Problem (VRP). Estamos perante um mercado cada vez mais competitivo, em que a satisfação das necessidades dos clientes aparece em primeiro lugar, assim, o tempo de entregas toma especial importância, mas do mesmo modo a otimização de recursos e redução de custos é cada vez mais importante para a sobrevivência das organizações. Esta dissertação apresenta, num contexto de logística, o problema de otimização de rotas com custos cumulativos, designado na literatura da especialidade por Cumulative Vehicle Routing Problem (CumVRP). Este problema, para além de permitir uma melhor otimização de rotas atendendo aos seus custos num todo, permite também, face a um VRP normal, obter o tempo mínimo de chegada aos clientes. E o problema mais indicado em termos de Logística Humanitária, em que é preciso gerir um conjunto de processos e sistemas envolvidos na mobilização de pessoas, recursos, habilidades e conhecimentos para socorrer vitimas de desastres, com o objetivo de estabelecer rotas que permitam no menor tempo possível chegar às áreas afetadas afim de poder prestar o socorro necessário.This dissertation addresses an important problem of logistic distribution, the problem of determination of optimal routes designated in the specialty literature for Vehicle Routing Problem (VRP). We are facing an increasingly competitive market, in which the satisfaction of customers’ needs is vital, thus the delivery time takes special importance, but likewise the resource optimization and cost reduction is increasingly important for the survival of organizations. This dissertation presents, in a context of logistics, the route optimization problem with cumulative costs, designated in the specialty literature by Cumulative Vehicle Routing Problem (CumVRP). This problem, in addition to allow a best route optimization in view of its costs in all, allows, in face of a normal VRP, the minimization of the arrival time to clients. This dissertation presents, in a context of logistics, the route optimization problem with cumulative costs, designated in the specialty literature by Cumulative Vehicle Routing Problem (CumVRP). This problem, in addition to allow a best route optimization in view of its costs in all, allows, in the face of a normal VRP, the minimization of arrival time to clients. Is the most suitable in terms of humanitarian logistics, where is necessary to manage a set of processes and systems involved in mobilizing people, resources, skills and knowledge to assist victims of disasters, with the aim of establishing routes that allow in the shortest time possible to reach the affected areas in order to be able to provide the help necessary.info:eu-repo/semantics/publishedVersio

Aproximación al Estado de Investigación en Logística Humanitaria: Un enfoque Bibliométrico

El presente proyecto, pretende el desarrollo de un estudio bibliométrico que permita identificar las bases conceptuales y las contribuciones relevantes en una de las áreas emergentes de la logística: La logística humanitaria. El proyecto seleccionará las principales publicaciones disponibles en Academic Search Complete, Emerald, Science Direct, y en las herramientas bibliográficas Scopus e ISI Web of Science con el acceso que ofrece la licencia de la Universidad Nacional de Colombia, para posteriormente, aplicar los principios de la bibliometría identificando las principales tendencias de investigación en el objeto de estudio seleccionado, utilizando indicadores y herramientas estadísticas descriptivas y mediciones de co-citación, detallando el contenido conceptual de cada artículo y estableciendo el estado de obsolescencia de la literatura disponible. Por último, la presente investigación realizará una discusión de los hallazgos de revisiones bibliográficas previas, frente a los resultados obtenidos en el desarrollo del presente estudio, de manera que se puedan identificar futuras líneas de investigación, orientadas hacia el desarrollo conceptual y solución de los retos que impone en la actualidad la logística humanitariaAbstract : The aim of this project is to develop a bibliometrics study that will be able to identify the conceptual bases and main contribution in one of the emerging areas of research in logistics known as Humanitarian logistics. This research paper will select the main publications in the databases available: Academic Search Complete, Emerald and Science Direct and other bibliographic tools as Scopus and ISI web of Science, by using the available access for the members of the National University of Colombia. Then applying the bibliometric principles, in order to bring out the main research trends of Humanitarian Logistics, using indicators and descriptive statistics tools and co-citation measurements, detailing the conceptual content of each publication and establishing the obsolescence level of the available literature. Finally, this research will propose a discussion regarding the findings of previous bibliographic reviews, compared to the results of the present study, in that manner that might help identify future research lines. These lines should be directed to the conceptual development and solution of the challenges that nowadays the humanitarian logistics facesMaestrí