Publications

Presentations

Below is a list of presentations I gave at different conferences, or invited talks during internships. Click on the title to be redirected to the slides proper, and on the “Abstract” button to see the abstract.

CIRRELT 2016

During my internship in Autumn 2016 at CIRRELT in Montréal, Canada, with professor Jean-François Cordeau, I was invited to give a talk on the BusPlus project, a public transportation network design problem for Canberra, Australia.

Abstract

Canberra is a planned city designed by American architect Walter Griffin in 1913. It features a large number of semi-autonomous towns separated by greenbelts. As a result, Canberra covers a wide geographic area, which makes public transportation particularly challenging.

We propose to tackle the problem of off-peak transportation by using a Bus and Shuttle network where buses will run between major hubs throughout the city at regular intervals, while a fleet of on-demand shuttles will take care of the “last mile” problem.

We first propose a model based on the Hub-Arc Location Problem (HALP). The HALP can be seen as a two-level decision problem deciding which arcs to open first and then how to route the flow at minimum cost. As such, its structure appears ideally suited for Benders decomposition.

Benders decomposition is a well-known partitioning method to solve large mixed integer programs. We develop a Benders decomposition approach with the following improvements: cut disaggregation, Pareto optimal sub-problem, and core point update.

VeRoLog 2016

During VeRoLog 2016, in Nantes, France, I presented our work on modelling a Rich VRP variant where constraints stemmed from a tender initiated by a grocery delivery company based in Queensland, Australia.

Abstract

In the classic Vehicle Routing Problem (VRP) a fleet of of vehicles has to visit a set of customers while minimising the operations’ costs. We study a rich variant of the VRP featuring split deliveries, an heterogeneous fleet, and vehicle-commodity incompatibility constraints. Our goal is twofold: define the cheapest routing and the most adequate fleet.

To do so, we split the problem into two interdependent components: a fleet design component and a routing component. First, we define two Mixed Integer Programming (MIP) formulations for each component. Then we discuss several improvements in the form of valid cuts and symmetry breaking constraints.

The main contribution of this paper is a comparison of the four resulting models for this Rich VRP. We highlight their strengths and weaknesses with extensive experiments.

Finally, we explore a lightweight integration with Constraint Programming (CP). We use a fast CP model which gives good solutions and use the solution to warm-start our models.