Browsing by Autor "Jorge A. Sefair"

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Car pooling optimization: A case study in Strasbourg (France)
(2008) Miguel A. Vargas; Jorge A. Sefair; Jose L. Walteros; Andrés L. Medaglia; Luis Rivera
Most of the cities around the world face mobility challenges, reflected in the ever increasing commuting times, and causing a dramatic environmental impact. At the same time, environmentally friendly individuals have become aware of the role they play in this problem and they are looking for new transportation alternatives. This is the case of a group of faculty in Strasbourg (France) who commute a significant distance from their home to their workplace and have found in car pooling a solution for their mobility problem. However, car pooling does not come for free. This group of commuters needs to come up with a timetable every two weeks, specifying the faculty who drive, the passengers in each car, the departing and returning time, taking into account multiple departing points and workplaces, and also, guaranteeing that each vehicle carries a prepaid toll card. After modeling the system as a network, two integer linear optimization models are proposed. The first one determines the best vehicle timetable, while the second model finds an efficient way in which the toll cards must be transferred.
Model for the Selection and Scheduling of Interdependent Projects
(2007) Andrea Zuluaga; Jorge A. Sefair; Andrés L. Medaglia
The selection and scheduling of interdependent projects is essential to any company's planning division. Project selection and scheduling is complex due to several reasons: presence of multiple decision criteria, business and operational constraints, and project interdependencies, for instance. Three types of project interdependencies can be identified: benefit, resource and technical interdependencies. Each type of interdependency is inherently different, adding difficulty to the modeling process. The proposed mixed-integer programming model is a tool for solving the problem of selecting and scheduling interdependent projects. The model chooses, from a bank of projects, those in which it is best to invest and also recommends when to invest. It maximizes the net present value of the portfolio of selected projects, which takes into account benefits and costs savings that may result from interdependencies between any pair of projects. The model satisfies time windows for starting dates, exogenous budget limits; endogenous cash flow generation and technical interdependence through the use of precedence relations and sets of mutually exclusive projects.