Search results for "HM"
showing 10 items of 10594 documents
Branch-and-Cut for the Split Delivery Vehicle Routing Problem with Time Windows
2019
The split delivery vehicle routing problem with time windows (SDVRPTW) is a notoriously hard combinatorial optimization problem. First, it is hard to find a useful compact mixed-integer programming (MIP) formulation for the SDVRPTW. Standard modeling approaches either suffer from inherent symmetries (mixed-integer programs with a vehicle index) or cannot exactly capture all aspects of feasibility. Because of the possibility to visit customers more than once, the standard mechanisms to propagate load and time along the routes fail. Second, the lack of useful formulations has rendered any direct MIP-based approach impossible. Up to now, the most effective exact algorithms for the SDVRPTW hav…
Heuristics for the capacitated modular hub location problem
2017
Abstract In this paper we study the hub location problem, where the goal is to identify an optimal subset of facilities (hubs) to minimize the transportation cost while satisfying certain capacity constraints. In particular, we target the single assignment version, in which each node in the transportation network is assigned to only one hub to route its traffic. We consider here a realistic variant introduced previously, in which the capacity of edges between hubs is increased in a modular way. This reflects the practical situation in air traffic where the number of flights between two locations implies a capacity in terms of number of passengers. Then, the capacity can be increased in a mo…
Branch-price-and-cut algorithms for the pickup and delivery problem with time windows and multiple stacks
2016
Abstract This paper proposes models and algorithms for the pickup and delivery vehicle routing problem with time windows and multiple stacks. Each stack is rear-loaded and is operated in a last-in-first-out (LIFO) fashion, meaning that when an item is picked up, it is positioned at the rear of a stack. An item can only be delivered if it is in that position. This problem arises in the transportation of heavy or dangerous material where unnecessary handling should be avoided, such as in the transportation of cars between car dealers and the transportation of livestock from farms to slaughterhouses. To solve this problem, we propose two different branch-price-and-cut algorithms. The first sol…
Applying particle swarm optimization to the motion-cueing-algorithm tuning problem
2017
The MCA tuning problem consists in finding the best values for the parameters/coefficients of Motion Cueing Algorithms (MCA). MCA are used to control the movements of robotic motion platforms employed to generate inertial cues in vehicle simulators. This problem is traditionally approached with a manual pilot-in-the-loop subjective tuning, based on the opinion of several pilots/drivers. Instead, this paper proposes applying Particle Swarm Optimization (PSO) to solve this problem, using simulated motion platforms and objective indicators rather than subjective opinions. Results show that PSO-based tuning can provide a suitable solution for this complex optimization problem.
Using Genetic Algorithms for Optimizing the PPC in the Highway Horizontal Alignment Design.
2016
Various studies have emphasized the interesting advantages related to the use of new transition curves for improving the geometric design of highway horizontal alignments. In a previous paper, one of the writers proposed a polynomial curve, called a polynomial parametric curve (PPC), proving its efficiency in solving several design problems characterized by a very complex geometry (egg-shaped transition, transition between reversing circular curves, semidirect and inner-loop connections, and so on). The PPC also showed considerable advantages from a dynamic perspective, as evidenced by the analysis of the main dynamic variables related to motion (as well as rate of change of radial accelera…
A GIS-Based Methodology to Estimate the Potential Demand of an Integrated Transport System
2017
In the design of a new public transport system or of an extension of an existing system, the choice of a suitable placement of stations and stops in the territory and the definition of the main axes are very important. The different choice in the number and distribution of the stops of a road transport system or of a railway transport system, in fact, makes the system more or less widespread and affects the consistency of the catchment area and the attractiveness of the system. The accessibility of a system, add to the reliability in providing the service, is the fundamental parameter influencing the modal split of the users. Therefore, the Public Administration must have tools able to eval…
Estimating the Demand for New Destinations for a Regional Airport Based on Its Catchment Area
2020
Abstract Estimating accurately demand both at market and company level for specific goods and services can be considered a necessity for every organization. Traditional demand estimation methods may not be relevant for estimating the demand for new destinations to be introduced by a regional airport. The present paper proposes to fill this gap and to develop the demand estimation literature by presenting a novel demand estimation method. Two research objectives are developed in this regard: (1) determining the catchment area of Sibiu International Airport (a regional airport in Romania) for destinations operated by competitor airports and not by Sibiu International Airport and (2) estimatin…
The Current and Future Role of Carsharing in Palermo: Analysis of Collected Data and Results of a Customer Satisfaction Survey
2018
In recent years many cities, both in Italy and abroad, have adopted Sustainable Urban Mobility Plans, in which one of the key action is the developing of the sharing mobility. The aim of the paper is to define the role that carsharing plays in Palermo today and it will play in the future, thanks to the adoption of new strategies, such as the introduction of the free-floating system, and transport demand orientation policies, such as the increase in the parking fees for private cars or the expansion of the ZTL. The average user profile of carsharing in Palermo has been identified through a customer satisfaction survey and the potential demand of carsharing in Palermo has been studied using G…
Probabilistic cross-validation estimators for Gaussian process regression
2018
Gaussian Processes (GPs) are state-of-the-art tools for regression. Inference of GP hyperparameters is typically done by maximizing the marginal log-likelihood (ML). If the data truly follows the GP model, using the ML approach is optimal and computationally efficient. Unfortunately very often this is not case and suboptimal results are obtained in terms of prediction error. Alternative procedures such as cross-validation (CV) schemes are often employed instead, but they usually incur in high computational costs. We propose a probabilistic version of CV (PCV) based on two different model pieces in order to reduce the dependence on a specific model choice. PCV presents the benefits from both…
Case Distribution and Nominalization: Evidence from Finnish
2009
. In many languages, case is distributed among many grammatical elements inside of argument DPs. This article shows that case distribution in Finnish is sensitive to certain nontrivial structural properties of those DPs. This makes it possible to use case distribution as a tool to investigate the internal structure of a variety of DPs, including nominalized clauses. It is argued, based on such new evidence, that (i) there exists a syntactic nominalizer head n within various kinds of nominal phrases, and that (ii) genitive argument DPs of nominalized clauses undergo raising analogous to the EPP-triggered DP raising in finite clauses. Furthermore, these genitive arguments are base-generated …