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Jeudi 23 Septembre
Heure: 10:30 - 11:30
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Design of diversified package tours for the digital travel industry : A branch-cut-and-price approach
Description: Laurent Alfandari Motivated by the revolution brought by the internet and communication technology in daily life, this paper examines how the online travel agencies (OTA) can use these technologies to improve customer value. We consider the design of a fixed number of package tours offered to customers in the digital travel industry. This can be formulated as a Team Orienteering Problem (TOP) with restrictions on budget and time. Different from the classical TOP, our work is the first one to introduce controlled diversity between tours. This enables the OTA to offer tourists a diversified portfolio of tour packages for a given period of time, each potential customer choosing a single tour in the selected set, rather than multiple independent tours over several periods as in the classical TOP. Tuning the similarity parameter between tours enables to manage the trade-off between individual preferences in consumers’ choices and economies of scale in agencies’ bargaining power. We propose compact and extended formulations and solve the master problem by a branch-and-price method, and an alternative branch-cut-and-price method. The latter uses a delayed dominance rule in the shortest path pricing problem solved by dynamic programming. A particularity of the model is that in the column generation phase, the diversity constraints hold between each pair of columns, which is unusual and requires to generate these constraints on the fly. Our methods are tested over benchmark TOP instances of the literature, and a real dataset collected from a Chinese OTA. We explore the impact of tours diversity on all stakeholders, and assess the computational performance of the various approaches.
Jeudi 14 Octobre
Heure: 10:30 - 11:30
Lieu: ATTENTION : Salle C311, bâtiment C, Université de Villetaneuse
Résumé: Incorporating Holding Costs in Continuous-Time Service Network Design: New Model, Relaxation and Exact Algorithm
Description: Roberto Baldacci The continuous-time service network design problem (CTSNDP) occurs widely in practice. It aims to minimize the total operational cost by optimizing schedules of transportation services and routes of shipments for dispatching, which can occur at any time point along a continuous planning horizon. In order to be cost effective, shipments often wait to be consolidated, which incurs holding cost. Despite its importance, the holding cost has not been taken into account in the existing studies on the CTSNDP, since introducing it will significantly complicate the problem and make the solution development very challenging.
To tackle this challenge, we develop a new dynamic discretization discovery algorithm, which can solve the CTSNDP with holding cost to exact optimum. The algorithm is based on a novel relaxation model and several new optimization techniques.
Results from extensive computational experiments validate the efficiency and effectiveness of the new algorithm, as well as demonstrating the benefits that can be gained by taking into account holding costs in solving the CTSNDP. In particular, we show that the significance of the benefits depends on the connectivity of the underline physical network and the flexibility of the shipments’ time requirements.