Heuristics for the capacitated modular hub location problem

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…

Scatter search for an uncapacitated p-hub median problem

Scatter search is a population-based method that has been shown to yield high-quality outcomes for combinatorial optimization problems. It uses strategies for combining solution vectors that have proved effective in a variety of problem settings. In this paper, we present a scatter search implementation for an NP -hard variant of the classic p-hub median problem. Specifically, we tackle the uncapacitated r-allocation p-hub median problem, which consists of minimizing the cost of transporting the traffics between nodes of a network through special facilities that act as transshipment points. This problem has a significant number of applications in practice, such as the design of transportati…

Improved polyhedral descriptions and exact procedures for a broad class of uncapacitated p-hub median problems

Abstract This work focuses on a broad class of uncapacitated p-hub median problems that includes non-stop services and setup costs for the network structures. In order to capture both the single and the multiple allocation patterns as well as any intermediate case of interest, we consider the so-called r-allocation pattern with r denoting the maximum number of hubs a terminal can be allocated to. We start by revisiting an optimization model recently proposed for the problem. For that model, we introduce several families of valid inequalities as well as optimality cuts. Moreover, we consider a relaxation of the model that contains several sets of set packing constraints. This motivates a pol…

Procedimento estratégico em três estágios de seleção de variáveis para a obtenção de resultados equilibrados na pesquisa em saúde pública

Multidisciplinary research in public health is approached using methods from many scientific disciplines. One of the main characteristics of this type of research is dealing with large data sets. Classic statistical variable selection methods, known as “screen and clean”, and used in a single-step, select the variables with greater explanatory weight in the model. These methods, commonly used in public health research, may induce masking and multicollinearity, excluding relevant variables for the experts in each discipline and skewing the result. Some specific techniques are used to solve this problem, such as penalized regressions and Bayesian statistics, they offer more balanced results a…

Heuristics for the min–max arc crossing problem in graphs

Abstract In this paper, we study the visualization of complex structures in the context of automatic graph drawing. Constructing geometric representations of combinatorial structures, such as networks or graphs, is a difficult task that requires an expert system. The automatic generation of drawings of graphs finds many applications from software engineering to social media. The objective of graph drawing expert systems is to generate layouts that are easy to read and understand. This main objective is achieved by solving several optimization problems. In this paper we focus on the most important one: reducing the number of arc crossings in the graph. This hard optimization problem has been…

Dietary Assesment of Free-Living Elderly Spanish People with Disabilities.

Nutritional research in elderly disabled is difficult in noninstitutionalized people. The dietary intake of a noninstitutionalized disabled population of the eastern region of Spain was evaluated to detect possible nutritional deviations. A total of 329 participants aged 65 and over were recruited. Most participants were overweight. Carbohydrates did not reach 50% of total Kcal/day. Insufficient micronutrient intakes and high consumption of simple carbohydrates and saturated fats (SFA) were found. A decreasing trend of water intake (p < .05) as well as an increasing trend of alcohol consumption (p < .05) with increasing age was found. The area of residence had a relevant impact on nutrition…

Professional counseling in women with serious mental illness: achieving a shift toward a more effective contraceptive method.

Mental disorders in reproductive-aged women have significant implications for the risk of unintended pregnancies. The objective of this study is to assess the professional counseling in clinical practice based on motivational interview in women with serious mental illness (SMI) in order to achieve a change to a more effective contraceptive method.A prospective observational cohort study (2012-2017) was conducted in a convenience sample of women with severe-moderate psychiatric disorders (After evidence-based counseling, 51.6% of participants changed their contraceptive method to a more effective one. This change was associated with gender violence (β coefficient = 1.58,Evidence-based contra…

The facility location problem with capacity transfers

Abstract This paper explores the concept of capacity transfer in the context of capacitated facility location problems. This is accomplished by assuming that facilities with surplus capacity/production can cooperate with those facing shortage by transferring part of that capacity/production. Such a transfer incurs a cost that nonetheless may be compensated by savings both in the installation costs and in the distribution costs. Mixed-integer mathematical programming models are proposed for the problem. A distinction is made between the case in which the triangle inequality holds for the transfer costs and the case in which it does not. We present compact models, which are enhanced with vali…

Models and solution methods for the uncapacitatedr-allocationp-hub equitable center problem

Hub networks are commonly used in telecommunications and logistics to connect origins to destinations in situations where a direct connection between each origin–destination (o-d) pair is impractical or too costly. Hubs serve as switching points to consolidate and route traffic in order to realize economies of scale. The main decisions associated with hub-network problems include (1) determining the number of hubs (p), (2) selecting the p-nodes in the network that will serve as hubs, (3) allocating non-hub nodes (terminals) to up to r-hubs, and (4) routing the pairwise o-d traffic. Typically, hub location problems include all four decisions while hub allocation problems assume that the valu…

Formulations and valid inequalities for the capacitated dispersion problem

This work focuses on the capacitated dispersion problem for which we study several mathematical formulations in different spaces using variables associated with nodes, edges, and costs. The relationships among the presented formulations are investigated by comparing the projections of the feasible sets of the LP relaxations onto the subspace of natural variables. These formulations are then strengthened with families of valid inequalities and variable-fixing procedures. The separation problems associated with the valid inequalities that are exponential in number are shown to be polynomially solvable by reducing them to longest path problems in acyclic graphs. The dual bounds obtained from s…

Heuristic Solutions for a Class of Stochastic Uncapacitated p-Hub Median Problems

In this work, we propose a heuristic procedure for a stochastic version of the uncapacitated r-allocation p-hub median problem with nonstop services. In particular, we assume that the number of hubs to which a terminal can be allocated is bounded from above by r. Additionally, we consider the possibility of shipping traffic directly between terminals (nonstop services). Uncertainty is associated with the traffic to be shipped between nodes and with the transportation costs. If we assume that such uncertainty can be captured by a finite set of scenarios, each of which with a probability known in advance, it is possible to develop a compact formulation for the deterministic equivalent proble…

Solutions for districting problems with chance-constrained balancing requirements

Abstract In this paper, a districting problem with stochastic demands is investigated. The goal is to divide a geographic area into p contiguous districts such that, with some given probability, the districts are balanced with respect to some given lower and upper thresholds. The problem is cast as a p -median problem with contiguity constraints that is further enhanced with chance-constrained balancing requirements. The total assignment cost of the territorial units to the representatives of the corresponding districts is used as a surrogate compactness measure to be optimized. Due to the tantalizing purpose of deriving a deterministic equivalent for the problem, a two-phase heuristic is d…

Heuristics for the capacitated dispersion problem

GRASP for the uncapacitated r-allocation p-hub median problem

In this paper we propose a heuristic for the Uncapacitated r-Allocation p-Hub Median Problem. In the classical p-hub location problem, given a set of nodes with pairwise traffic demands, we must select p of them as hub locations and route all traffics through them at a minimum cost. We target here an extension, called the r-allocation p-hub median problem, recently proposed by Yaman [19], in which every node is assigned to r of the p selected hubs (r@?p) and we are restricted to route the traffic of the nodes through their associated r hubs. As it is usual in this type of problems, our method has three phases: location, assignment and routing. Specifically, we propose a heuristic based on t…

Nutrients associated with diseases related to aging: a new healthy aging diet index for elderly population

espanolIntroduccion: suelen usarse diversos indices dieteticos para medir la calidad de la nutricion en edades avanzadas. Sin embargo, ninguno de ellos fue disenado para evaluar la nutricion con el objetivo de evitar discapacidades en la poblacion anciana. Objetivos: identificar en la literatura cientifica los “nutrientes e ingestas” involucrados en el envejecimiento, asi como proponer un nuevo indice, considerando esta informacion, que sirva para evaluar la calidad de la nutricion con objeto de prevenir enfermedades relacionadas con el envejecimiento. Metodos: se realizo una revision bibliografica, obteniendo informacion sobre los nutrientes asociados con el envejecimiento. Todos estos nut…

Effect of cost on early removal of contraceptive implants: a prospective cohort study

OBJECTIVES To evaluate the effect of the cost of subdermal etonogestrel implant (SEI) on the continuation rate one year after insertion, and to assess the reasons given by users to remove the implant before the expiration date. METHODS Prospective cohort study conducted among 265 women who chose the SEI as a contraceptive method in a sexual and reproductive health center in the eastern region of Spain, between October/2012 and October/2017. The sample was divided into two cohorts depending on the cost of the implant for the user (free-of-charge or requiring partial payment). Kaplan-Meier survival curves were used to compare the cumulative removal rates of free implants with partially paid i…

Adherence to dietary treatment and clinical factors associated with anti-transglutaminase antibodies in celiac disease during the follow-up

Introduction In clinical practice, celiac disease (CD) is monitored through anti-transglutaminase (TGA-IgA) antibody levels. The normalization of serum levels in successive periodic measurements indicates good response and adherence to dietary treatment. Objectives To evaluate the factors associated with the evolution of TGA-IgA antibodies and their association with dietary non-compliance and diseases related to CD. Methods This prospective observational study was carried out in 254 participants, who were recruited from patients from a hospital in southern Spain. Information about sex, age, serological test results, HLA DQ2/DQ8 haplotypes, mucosal atrophy, gastrointestinal and extra-intesti…

Geographic conditioning in dietary, social, and health patterns in elderly population with disabilities

Abstract Objective The aim of this study was to identify the most relevant variables defining the dietary, social, and health patterns of elderly populations with disabilities, considering their geographic profile. Methods A cross-sectional study was carried out in a sample of 354 disabled, free-living elderly adults from three different geographic profiles (metropolitan, rural, and mixed profile). The dietary data were obtained through a validated food habit questionnaire. The data regarding health status, cohabitation unit, and social benefits were obtained through the public social services. A standardized principal component analysis was used to select the most relevant variables, by co…