A Local Search Modeling for Constrained Optimum Paths Problems (Extended Abstract)

Constrained Optimum Path (COP) problems appear in many real-life applications, especially on communication networks. Some of these problems have been considered and solved by specific techniques which are usually difficult to extend. In this paper, we introduce a novel local search modeling for solving some COPs by local search. The modeling features the compositionality, modularity, reuse and strengthens the benefits of Constrained-Based Local Search. We also apply the modeling to the edge-disjoint paths problem (EDP). We show that side constraints can easily be added in the model. Computational results show the significance of the approach

The Resource constrained shortest path problem implemented in a lazy functional language

The resource constrained shortest path problem is an NP-hard problem for which many ingenious algorithms have been developed. These algorithms are usually implemented in FORTRAN or another imperative programming language. We have implemented some of the simpler algorithms in a lazy functional language. Benefits accrue in the software engineering of the implementations. Our implementations have been applied to a standard benchmark of data files, which is available from the Operational Research Library of Imperial College, London. The performance of the lazy functional implementations, even with the comparatively simple algorithms that we have used, is competitive with a reference FORTRAN implementation

On Alternative Formulations to the Shortest Path Problem with Time Windows and Capacity Constraints

The elementary shortest-path problem with time-windows and capac-ity constraints is a problem used for solving vehicle-routing and crew-scheduling applications. It occurs as a sub-problem used to implicitly generate the set of all feasible routes and schedules in the column-generation formulation of the vehicle routing problem with time windows and its variations. In the problem there is a directed graph with a source node and a destination node, and each arc has a cost and a vector of weights specifying its requirements of a resource with a finite capacity. A minimum cost source–destination directed path is sought such that the total consumption of the resource does not exceed the capacity. The problem ins NP-hard in the strong sense. We review integer-linear formulation to the problem and compare them in order to study their computational efficiency.Sociedad Argentina de Informática e Investigación Operativ

On Alternative Formulations to the Shortest Path Problem with Time Windows and Capacity Constraints

The elementary shortest-path problem with time-windows and capac-ity constraints is a problem used for solving vehicle-routing and crew-scheduling applications. It occurs as a sub-problem used to implicitly generate the set of all feasible routes and schedules in the column-generation formulation of the vehicle routing problem with time windows and its variations. In the problem there is a directed graph with a source node and a destination node, and each arc has a cost and a vector of weights specifying its requirements of a resource with a finite capacity. A minimum cost source–destination directed path is sought such that the total consumption of the resource does not exceed the capacity. The problem ins NP-hard in the strong sense. We review integer-linear formulation to the problem and compare them in order to study their computational efficiency.Sociedad Argentina de Informática e Investigación Operativ

On Alternative Formulations to the Shortest Path Problem with Time Windows and Capacity Constraints

The elementary shortest-path problem with time-windows and capac-ity constraints is a problem used for solving vehicle-routing and crew-scheduling applications. It occurs as a sub-problem used to implicitly generate the set of all feasible routes and schedules in the column-generation formulation of the vehicle routing problem with time windows and its variations. In the problem there is a directed graph with a source node and a destination node, and each arc has a cost and a vector of weights specifying its requirements of a resource with a finite capacity. A minimum cost source–destination directed path is sought such that the total consumption of the resource does not exceed the capacity. The problem ins NP-hard in the strong sense. We review integer-linear formulation to the problem and compare them in order to study their computational efficiency.Sociedad Argentina de Informática e Investigación Operativ

Delay Management in Public Transportation: Service Regularity Issues and Crew Re-scheduling

In this paper, we propose a decision support tool to assist a local public transportation company in tackling service delays and small disruptions. We discuss different ways to assess and improve the regularity of the service, and we propose a simulation based optimization system that can be effectively used in a real-time environment taking into account both vehicle and driver shifts. In particular, we describe a tabu-search procedure for the online vehicle scheduling optimizing the regularity of the service and a column generation approach for the consequential crew re-scheduling minimizing the driver extra-time. As a case study, we analyze the management of urban surface lines of Azienda Trasporti Milanese (ATM) of Milan. In the last part of the paper we report a detailed analysis of the experimental phase showing the effectiveness of the proposed approach