A metaheuristic for crew scheduling in a pickup-and-delivery problem with time windows

A vehicle routing and crew scheduling problem (VRCSP) consists of simultaneously planning the routes of a fleet of vehicles and scheduling the crews, where the vehicle-crew correspondence is not fixed through time. This allows a greater planning flexibility and a more efficient use of the fleet, but in counterpart, a high synchronisation is demanded. In this work, we present a VRCSP where pickup-and-delivery requests with time windows have to be fulfilled over a given planning horizon by using trucks and drivers. Crews can be composed of 1 or 2 drivers and any of them can be relieved in a given set of locations. Moreover, they are allowed to travel among locations with non-company shuttles, at an additional cost that is minimised. As our problem considers distinct routes for trucks and drivers, we have an additional flexibility not contemplated in other previous VRCSP given in the literature where a crew is handled as an indivisible unit. We tackle this problem with a two-stage sequential approach: a set of truck routes is computed in the first stage and a set of driver routes consistent with the truck routes is obtained in the second one. We design and evaluate the performance of a metaheuristic based algorithm for the latter stage. Our algorithm is mainly a GRASP with a perturbation procedure that allows reusing solutions already found in case the search for new solutions becomes difficult. This procedure together with other to repair infeasible solutions allow us to find high-quality solutions on instances of 100 requests spread across 15 cities with a fleet of 12-32 trucks (depending on the planning horizon) in less than an hour. We also conclude that the possibility of carrying an additional driver leads to a decrease of the cost of external shuttles by about 60% on average with respect to individual crews and, in some cases, to remove this cost completely

Solving the List Coloring Problem through a Branch-and-Price algorithm

In this work, we present a branch-and-price algorithm to solve the weighted version of the List Coloring Problem, based on a vertex cover formulation by stable sets. This problem is interesting for its applications and also for the many other problems that it generalizes, including the well-known Graph Coloring Problem. With the introduction of the concept of indistinguishable colors, some theoretical results are presented which are later incorporated into the algorithm. We propose two branching strategies based on others for the Graph Coloring Problem, the first is an adaptation of the one used by Mehrotra and Trick in their pioneering branch-and-price algorithm, and the other is inspired by the one used by M\'endez-D\'iaz and Zabala in their branch-and-cut algorithm. The rich structure of this problem makes both branching strategies robust. Extended computation experimentation on a wide variety of instances shows the effectiveness of this approach and evidences the different behaviors that the algorithm can have according to the structure of each type of instance

Planning the workday of bus drivers by a graph list-coloring model

In this work, we address the problem of planning the workday of bus drivers in argentinian intercity bus transport companies. In particular, we focus on a company which needs to fulfill roughly 800 trips per day between 3 cities of the Province of Buenos Aires with a stuff of around 200 drivers and 100 buses. Planning consists of assigning one driver to each trip in a way the driver performs all the trips without scheduling conflicts and minimizing the overall amount of overtime among all bus drivers. We model the problem as a particular Graph Coloring Problem and we propose an Integer Linear Programming formulation. Computations experiments show that this formulation outperforms other ones given in the literature for the same problem. In order to address large instances as the one given by the company, we also propose a heuristic algorithm that delivers better solutions than the company actually uses in a reasonably amount of time. The heuristic has two phases where the first one constructs an initial solution and the second one improves the solution iteratively.Fil: Lucci, Mauro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario; ArgentinaFil: Nasini, Graciela Leonor. Universidad Nacional de Rosario. Facultad de Ciencias Exactas, Ingeniería y Agrimensura; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario; ArgentinaFil: Severin, Daniel Esteban. Universidad Nacional de Rosario. Facultad de Ciencias Exactas, Ingeniería y Agrimensura; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario; Argentin

A Branch and Price Algorithm for List Coloring Problem

Coloring problems in graphs have been used to model a wide range of real applications. In particular, the List Coloring Problem generalizes the well-known Graph Coloring Problem for which many exact algorithms have been developed. In this work, we present a Branch-and-Price algorithm for the weighted version of the List Coloring Problem, based on the one developed by Mehrotra and Trick (1996) for the Graph Coloring Problem. This version considers non-negative weights associated to each color and it is required to assign a color to each vertex from predetermined lists in such a way the sum of weights of the assigned colors is minimum. Computational experiments show the good performance of our approach, being able to comfortably solve instances whose graphs have up to seventy vertices. These experiences also bring out that the hardness of the instances of the List Coloring Problem does not seem to depend only on quantitative parameters such as the size of the graph, its density, and the size of list of colors, but also on the distribution of colors present in the lists.Fil: Lucci, Mauro. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Rosario. Facultad de Ciencias Exactas Ingeniería y Agrimensura. Escuela de Ciencias Exactas y Naturales. Departamento de Matemática; ArgentinaFil: Nasini, Graciela Leonor. Universidad Nacional de Rosario. Facultad de Ciencias Exactas Ingeniería y Agrimensura. Escuela de Ciencias Exactas y Naturales. Departamento de Matemática; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Severin, Daniel Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Rosario. Facultad de Ciencias Exactas Ingeniería y Agrimensura. Escuela de Ciencias Exactas y Naturales. Departamento de Matemática; Argentina10th Latin and American Algorithms, Graphs and Optimization Symposium (LAGOS 2019)Belo HorizonteBrasilCoordenação de Aperfeiçoamento de Pessoal de Nivel SuperiorConselho Nacional de Desenvolvimento Científico e Técnologico do BrasilUniversidade Federal de Minas Gerai

Metaheurística para la asignación de tripulaciones en un problema de recolección y entrega de mercaderías con ventanas de tiempo y cambios de tripulación

En este trabajo se propone un algoritmo basado en la metaheurística GRASP que, asumiendo fijo un plan de rutas para los camiones, decida relevos válidos para la tripulación a lo largo del horizonte de planificación y minimice el costo que acarrea el traslado del personal en vehículos externos a la flota. Adicionalmente, sobre las soluciones alcanzadas se propone un algoritmo de mejoramiento basado en una búsqueda local que intenta arreglar ciertos traslados externos evitables.Sociedad Argentina de Informática e Investigación Operativ

Formulaciones de PLE para un abordaje simultáneo en un problema de ruteo de vehículos con cambios de tripulación

Una compañía dedicada a la distribución de café dispone de una flota homogénea de camiones y de una planta de conductores que deben ser organizados para cumplir con un conjunto de solicitudes de recolección-y-entrega de mercadería con ventanas de tiempo. El objetivo es encontrar una asignación óptima para estos recursos que minimice los costos operativos, sujeto a una serie de restricciones operativas y laborales. Las tripulaciones pueden estar conformadas por uno o dos conductores y cada uno de ellos puede ser relevado durante el recorrido. Adicionalmente, los conductores pueden utilizar transportes externos a la compañía, por un costo adicional que se desea minimizar. Es frecuente en la literatura la aplicación de un abordaje secuencial para resolver este tipo de problemas. Una primera etapa involucra rutear los camiones, ignorando las restricciones de los conductores, y sobre las rutas previamente construidas se asignan las tripulaciones en una segunda etapa. Esto resulta en dos subproblemas más fáciles de resolver, pero sin garantía de optimalidad global ni de factibilidad (la segunda etapa podría resultar infactible a partir de las rutas determinadas en la primera). Por el contrario, un abordaje simultáneo ha sido mucho menos estudiado en la literatura. Este último supone un gran desafío desde un punto de vista computacional, dado que emergen complejas restricciones de sincronización entre los recursos. Partiendo de modelos matemáticos basados en teoría de grafos, se presentarán dos formulaciones de PLE compactas para el problema en estudio, siguiendo un abordaje simultáneo. Mediante experiencias computacionales, las formulaciones serán comparadas sobre diversas instancias de prueba resueltas con un solver específico, a fin de determinar cuál de ellas resulta más competitiva para futuros desarrollos.Sociedad Argentina de Informática e Investigación Operativ

Metaheurística para la asignación de tripulaciones en un problema de recolección y entrega de mercaderías con ventanas de tiempo y cambios de tripulación

En este trabajo se propone un algoritmo basado en la metaheurística GRASP que, asumiendo fijo un plan de rutas para los camiones, decida relevos válidos para la tripulación a lo largo del horizonte de planificación y minimice el costo que acarrea el traslado del personal en vehículos externos a la flota. Adicionalmente, sobre las soluciones alcanzadas se propone un algoritmo de mejoramiento basado en una búsqueda local que intenta arreglar ciertos traslados externos evitables.Sociedad Argentina de Informática e Investigación Operativ

Type of hospitalisations and in-hospital outcomes in the Italian coronary care unit network at the time of COVID-19 pandemic: the BLITZ-COVID19 Registry

The aim of the study was to describe the epidemiology and outcome of patients hospitalised during the COVID-19 pandemic in intensive cardiac care units (ICCs)

Prescription appropriateness of anti-diabetes drugs in elderly patients hospitalized in a clinical setting: evidence from the REPOSI Register

Diabetes is an increasing global health burden with the highest prevalence (24.0%) observed in elderly people. Older diabetic adults have a greater risk of hospitalization and several geriatric syndromes than older nondiabetic adults. For these conditions, special care is required in prescribing therapies including anti- diabetes drugs. Aim of this study was to evaluate the appropriateness and the adherence to safety recommendations in the prescriptions of glucose-lowering drugs in hospitalized elderly patients with diabetes. Data for this cross-sectional study were obtained from the REgistro POliterapie-Società Italiana Medicina Interna (REPOSI) that collected clinical information on patients aged ≥ 65 years acutely admitted to Italian internal medicine and geriatric non-intensive care units (ICU) from 2010 up to 2019. Prescription appropriateness was assessed according to the 2019 AGS Beers Criteria and anti-diabetes drug data sheets.Among 5349 patients, 1624 (30.3%) had diagnosis of type 2 diabetes. At admission, 37.7% of diabetic patients received treatment with metformin, 37.3% insulin therapy, 16.4% sulfonylureas, and 11.4% glinides. Surprisingly, only 3.1% of diabetic patients were treated with new classes of anti- diabetes drugs. According to prescription criteria, at admission 15.4% of patients treated with metformin and 2.6% with sulfonylureas received inappropriately these treatments. At discharge, the inappropriateness of metformin therapy decreased (10.2%, P < 0.0001). According to Beers criteria, the inappropriate prescriptions of sulfonylureas raised to 29% both at admission and at discharge. This study shows a poor adherence to current guidelines on diabetes management in hospitalized elderly people with a high prevalence of inappropriate use of sulfonylureas according to the Beers criteria