1,721,198 research outputs found
The multivisit drone routing problem with edge launches: An iterative approach with discrete and continuous improvements
No full textIn recent years, the usage of drones in last-mile logistics has stirred great interest in the operations research community. Many papers have considered schemes of hybrid truck-and-drone delivery. In this paper, we focus on the Multivisit Drone Routing Problem with Edge Launches (MVDRP-EL) which assumes: a heterogenous set of packages, a drone capable of carrying multiple packages at a time and that can be launched and retrieved along an edge, a flexible launch/retrieval site set, and a user-defined energy depletion function. We believe this paper is the first to exploit edge launch ability through a global continuous approach. In this context, we propose an original formulation based on the Covering Salesman Problem to compute a valid lower bound for the problem and an iterative solution method to determine a MVDRP-EL solution with quality launch/retrieval sites along the road network edges. Each iteration of the solution method consists of two phases. In the first phase, the road network edges are discretized to obtain launch/retrieval sites, and a first solution is determined. In the second phase, the truck route is set and we reduce the completion time by carefully synchronizing truck and drone routes by solving an original Mixed Integer Second Order Cone Program. The lower bound formulation and the proposed method have been tested on several instances and results indicate the effectiveness of the proposed method and the potential value of launching along an edge, respectively
An improved model for estimating optimal VRP solution values
No full textSince it is computationally expensive to solve the vehicle routing problem (VRP) optimally, as this problem is NP-hard, in this technical note we study how to accurately approximate the optimal VRP tour length. In our previous papers, we developed a linear regression model including the mean and standard deviation of the modified Clarke and Wright heuristic solution values, which was able to predict the optimal VRP tour length fairly well. In this note, we find that by doing a small amount of extra work to include the minimum of the modified Clarke and Wright heuristic solution values, we can improve the predictive results substantially
Estimating optimal split delivery vehicle routing problem solution values
No full textThis paper explores the application of linear regression models to estimate the optimal solution value (i.e., the sum of tour lengths) for the Split Delivery Vehicle Routing Problem (SDVRP). We present novel models that integrate topological features along with the mean and standard deviation of feasible solution values, achieving an impressive accuracy with an error margin of approximately 3%. To obtain random feasible solutions for the SDVRP quickly, we propose a modified Clarke & Wright algorithm with split delivery (MCWSD). Our results demonstrate the potential of extending our earlier work to more complex routing problems, highlighting the importance of incorporating diverse features to obtain accurate approximations
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Using regression models to understand the impact of route-length variability in practical vehicle routing
No full textIn this short paper, we use regression models to highlight a key point in practical vehicle routing. In particular, we focus on an important problem experienced by delivery and service companies. These companies dispatch vehicles to deliver products and provide services to customers. For the capacitated vehicle routing problem, we show that reducing route-length variability while generating vehicle routes is an important consideration to minimize the total operating and delivery costs for a company encountering random traffic
Partitioning a street network into compact, balanced, and visually appealing routes
No full textIn practice, it is often desirable for the routes of vehicles to be compact and separate. A set of routes is compact if the streets serviced by each route are geographically clustered, and separated if the routes overlap minimally. We consider the Min–Max K Windy Rural Postman Problem (MMKWRPP), in which the objective is to route a homogeneous fleet of K vehicles such that the cost of the longest route is minimized. We develop a heuristic that is algorithmically simple, produces solutions that are comparable in quality to those produced by an existing approach, and performs well with respect to metrics that quantify compactness and separation. Our heuristic uses a partitioning scheme in which the weight of a vertex includes contributions from both incident streets requiring service and the distance needed to travel to a vertex. We present computational results for a set of instances that we generate from real-world street networks and for a set of artificial instances. Our code is part of the Open-source Arc Routing Library (OAR Lib) at https://github.com/Olibear/ArcRoutingLibrary. © 2017 Wiley Periodicals, Inc. NETWORKS, Vol. 69(3), 290–303 2017
Modeling and solving the intersection inspection rural postman problem
No full textLocal governments inspect roads to decide which segments and intersections to repair. Videos are taken using a camera mounted on a vehicle. The vehicle taking the videos proceeds straight or takes a left turn to cover an intersection fully. We introduce the intersection inspection rural postman problem (IIRPP), which is a new variant of the rural postman problem (RPP) that involves turns. We develop integer programming formulations of the IIRPP based on two different graph transformations to generate least-cost vehicle routes. One formulation is based on a new idea of transforming a graph. A second formulation is based on a graph transformation idea from the literature. Computational experiments show that the formulation involving the new graph transformation idea performs much better than the other formulation. We also develop an RPP-based heuristic and a heuristic based on a modified RPP. Heuristic solutions are improved by solving integer programming formulations on an induced subgraph. Computational experiments show that the heuristics based on the modified RPP perform much better than the RPP-based heuristics. The best-performing heuristic generates very good quality IIRPP-feasible routes on large street networks quickly
- …
