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

Propuesta de enseñanza de la formalización de la matemática utilizando un asistente de pruebas en estudiantes de la Licenciatura en Ciencias de la Computación

En este trabajo proponemos realizar una actividad con estudiantes de Cs. de la Computación en donde se plantea la importancia de la formalización de la Matemática, y su abordaje a través del asistente de pruebas Coq. El objetivo es lograr que los estudiantes conozcan la existencia de este tipo de herramientas, adquieran destreza en formalizar las definiciones y enunciados, y puedan realizar pruebas formales de enunciados sencillos.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

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

A polyhedral approach for the Equitable Coloring Problem

In this work we study the polytope associated with a 0,1-integer programming formulation for the Equitable Coloring Problem. We find several families of valid inequalities and derive sufficient conditions in order to be facet-defining inequalities. We also present computational evidence that shows the efficacy of these inequalities used in a cutting-plane algorithm

Formalization of the Domination Chain with Weighted Parameters

The Cockayne-Hedetniemi Domination Chain is a chain of inequalities between classic parameters of graph theory: for a given graph G, ir(G) ≤ γ(G) ≤ ι(G) ≤ α(G) ≤ Γ(G) ≤ IR(G). These parameters return the maximum/minimum cardinality of a set satisfying some property. However, they can be generalized for graphs with weighted vertices where the objective is to maximize/minimize the sum of weights of a set satisfying the same property, and the domination chain still holds for them. In this work, the definition of these parameters as well as the chain is formalized in Coq/Ssreflect.Fil: Severín, Daniel. Universidad Nacional de Rosario. FCEIA. CONICET. Rosario; Argentin

Cross-identification of stellar catalogs with multiple stars: Complexity and Resolution

In this work, I present an optimization problem which consists of assigning entries of a stellar catalog to multiple entries of another stellar catalog such that the probability of such assignment is maximum. I show a way of modeling it as a Maximum Weighted Stable Set Problem which is further used to solve a real astronomical instance and I partially characterize the forbidden subgraphs of the resulting family of graphs given by that reduction. Finally, I prove that the problem is NP-Hard.Fil: Severín, Daniel. Universidad Nacional de Rosario. FCEIA. CONICET. Rosario; Argentin