References of "Schyns, Michael"
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See detailAccounting for price endogeneity in airline itinerary choice models
Lurkin, Virginie ULg; Garrow, Laurie; Higgins, Matthew et al

Conference (2016, May 20)

This study formulates an itinerary choice model that is consistent with those used by industry and corrects for price endogeneity using a control function that uses several types of instrumental variables ... [more ▼]

This study formulates an itinerary choice model that is consistent with those used by industry and corrects for price endogeneity using a control function that uses several types of instrumental variables. We estimate our models using database of more than 3 million tickets provided by the Airlines Reporting Corporation. Results based on Continental U.S. markets for May 2013 departures show that models that fail to account for price endogeneity overestimate customers’ value of time and result in biased price estimates and incorrect pricing recommendations. Extensions to advanced discrete choice models show the importance of accounting for inter-alternative substitution for products that share similar departure times. [less ▲]

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See detailEarly Detection of University Students in Potential Difficulty
Hoffait, Anne-Sophie ULg; Schyns, Michael ULg

E-print/Working paper (2016)

Using data mining methods, this paper presents a new means of identifying freshmen's profiles likely to face major difficulties to complete their first academic year. Academic failure is a relevant issue ... [more ▼]

Using data mining methods, this paper presents a new means of identifying freshmen's profiles likely to face major difficulties to complete their first academic year. Academic failure is a relevant issue at a time when post-secondary education is ever more critical to economic success. We aim at early detection of potential failure using student data available at registration, i.e. school records and environmental factors, with a view to timely and efficient remediation and/or study reorientation. For the sake of accuracy, we adapt three data mining methods, namely random forest, logistic regression and artificial neural network algorithms. Real data pertaining to undergraduates at the University of Liège (Belgium), illustrates our methodology. [less ▲]

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See detailA Comparison of Departure Time of Day Formulations
Lurkin, Virginie ULg; Garrow, Laurie; Higgins, Matthew et al

E-print/Working paper (2016)

Airline passengers’ itinerary choices are influenced by many factors including carriers, prices, the number of connections, and departure times. This paper compares three different methods that have been ... [more ▼]

Airline passengers’ itinerary choices are influenced by many factors including carriers, prices, the number of connections, and departure times. This paper compares three different methods that have been used to model departure time of day preferences. The first is a discrete formulation that uses indicator variables to represent the hour of departure. The next two methods are based on a continuous formulation that uses a series of sine and cosine functions. One assumes departure time preferences over a 24-hour cycle and the other uses shorter cycle lengths that account for fewer departures during certain hours of the day. We compare models using itineraries in the Continental U.S. that are separated by two time zones. Although the discrete formulation fits the data better, the two continuous time of day formulations are preferred as they provide more intuitive predictions and require fewer parameters. Results between the two continuous time of day formulations are similar but differ in how strongly they weight itineraries that depart very early or very late in the day. Based on empirical results, we recommend testing both 24-hour and less than 24-hour cycle lengths for a particular dataset. [less ▲]

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See detailAccounting for Price Endogeneity in Airline Itinerary Choice Models: An Application to Continental U.S. Markets
Lurkin, Virginie ULg; Garrow, Laurie; Higgins, Matthew et al

E-print/Working paper (2016)

Network planning models, which forecast the profitability of airline schedules, support many critical decisions, including equipment purchase decisions. Network planning models include an itinerary choice ... [more ▼]

Network planning models, which forecast the profitability of airline schedules, support many critical decisions, including equipment purchase decisions. Network planning models include an itinerary choice model which is used to allocate air total demand in a city pair to different itineraries. Multinomial logit (MNL) models are commonly used in practice and capture how individuals make trade-offs among different itinerary attributes; however, none that we are aware of account for price endogeneity. This study formulates an itinerary choice model that is consistent with those used by industry and corrects for price endogeneity using a control function that uses several types of instrumental variables. We estimate our models using database of more than 3 million tickets provided by the Airlines Reporting Corporation. Results based on Continental U.S. markets for May 2013 departures show that models that fail to account for price endogeneity overestimate customers’ value of time and result in biased price estimates and incorrect pricing recommendations. The size and comprehensiveness of our database allows us to estimate highly refined departure time of day preference curves that account for distance, direction of travel, the number of time zones traversed, departure day of week and itinerary type (outbound, inbound or one-way). These time of day preference curves can be used by airlines, researchers, and government organizations in the evaluation of different policies such as congestion pricing. [less ▲]

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See detailContinuous Departure Time of Day Preferences for Continental U.S. Airline Markets Segmented by Distance, Direction of Travel, Number of Time Zones, Day of Week and Itinerary Type
Lurkin, Virginie ULg; Garrow, Laurie; Higgins, Matthew et al

E-print/Working paper (2016)

Airlines use itinerary choice models to allocate the total number of passengers in a city pair to specific itineraries. In a related paper, we estimated a multinomial logit (MNL) itinerary choice model ... [more ▼]

Airlines use itinerary choice models to allocate the total number of passengers in a city pair to specific itineraries. In a related paper, we estimated a multinomial logit (MNL) itinerary choice model using database of more than 3 million tickets for Continental U.S. markets provided by the Airlines Reporting Corporation that accounted for price endogeneity. The size and comprehensiveness of our database allowed us to estimate highly refined continuous departure time of day preference curves that account for distance, direction of travel, the number of time zones traversed, departure day of week and itinerary type (outbound, inbound or one-way). This paper and accompanying Excel spreadsheet located at http://garrowlab.ce.gatech.edu contain the results of all model coefficients (including the 1260 time of day parameters) and summarize results in a series of ten figures. These highly-refined time of day preference curves can be used by airlines, researchers, and government organizations in the evaluation of demand-management and other policies. [less ▲]

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See detailA Mixed Integer Programming formulation for the three dimensional bin packing problem deriving from an air cargo application
Paquay, Célia ULg; Schyns, Michael ULg; Limbourg, Sabine ULg

in International Transactions in Operational Research (2016), 23(1-2), 187-213

The present paper looks into the problem of optimising the loading of boxes into containers. The goal is to minimise the unused volume. This type of problem belongs to the family of Multiple Bin Size Bin ... [more ▼]

The present paper looks into the problem of optimising the loading of boxes into containers. The goal is to minimise the unused volume. This type of problem belongs to the family of Multiple Bin Size Bin Packing Problems. The approach includes an extensive set of constraints encountered in real-world applications in the three-dimensional case: the stability, the fragility of the items, the weight distribution and the possibility to rotate the boxes. It also includes the specific situation in which containers are truncated parallelepipeds. This is typical in the field of air transportation. While most papers on cutting and packing problems describe ad-hoc procedures, this paper proposes a mixed integer linear program. The validity of this model is tested on small instances. [less ▲]

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See detailAn Ant Colony System for Responsive Dynamic Vehicle Routing
Schyns, Michael ULg

in European Journal of Operational Research (2015), 245(3), 704-718

We present an algorithm based on an Ant Colony System to deal with a broad range of Dynamic Capacitated Vehicle Routing Problems with Time Windows, (partial) Split Delivery and Heterogeneous fleets ... [more ▼]

We present an algorithm based on an Ant Colony System to deal with a broad range of Dynamic Capacitated Vehicle Routing Problems with Time Windows, (partial) Split Delivery and Heterogeneous fleets (DVRPTWSD). Besides the traditional distance criterion, we address the important case of responsiveness. Responsiveness is defined here as completing a delivery as soon as possible, within the time window, such that the client or the truck may restart its activities. This is crucial for many production or service activities in different fields: express parcel deliveries, taxi services, Just in Time production, express repair services, medical care, petrol station replenishment, etc. We develop an interactive web-based solution to allow dispatchers to take new information into account in real-time. The algorithm and its parametrization were tested on real and artificial instances. We first illustrate our approach with a problem submitted by Liege Airport, the 8th biggest cargo airport in Europe. The goal is to develop a decision system to optimize the journey of the refueling trucks. We then consider some classical VRP benchmarks with extensions for more complex problems. [less ▲]

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See detailEstimation of Airline Itinerary Choice Models Using Disaggregate Ticket Data
Lurkin, Virginie ULg; Garrow, Laurie A.; Higgins, Matthew J. et al

in 55th AGIFORS Annual Proceedings 2015 (2015, August 29)

Airline itinerary choice models support many multi-million dollar decisions, i.e., they are used to evaluate potential route schedules. Classic models suffer from major limitations, most notably they use ... [more ▼]

Airline itinerary choice models support many multi-million dollar decisions, i.e., they are used to evaluate potential route schedules. Classic models suffer from major limitations, most notably they use average fare information but to not correct for price endogeneity. We use a novel database of airline tickets to estimate itinerary choice models using detailed fare data and compare these to classic itinerary choice models that use aggregate fare information but correct for price endogeneity. [less ▲]

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See detailThe Airline Container Loading Problem with Pickup and Delivery
Lurkin, Virginie ULg; Schyns, Michael ULg

in European Journal of Operational Research (2015), 244(3), 955-965

This paper considers the loading optimization problem for a set of containers and pallets transported into a cargo aircraft that serves multiple airports. Because of pickup and delivery operations that ... [more ▼]

This paper considers the loading optimization problem for a set of containers and pallets transported into a cargo aircraft that serves multiple airports. Because of pickup and delivery operations that occur at intermediate airports, this problem is simultaneously a Weight & Balance Problem and a Sequencing Problem. Our objective is to minimize fuel and handling operation costs. This problem is shown to be NP-hard. We resort to a mixed integer linear program. Based on real-world data from a professional partner (TNT Airways), we perform numerical experiments using a standard B&C library. This approach yields better solutions than traditional manual planning, which results in substantial cost savings. [less ▲]

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See detailProceedings of the 12th Workshop on Models and Algorithms for Planning and Scheduling Problems
Marchetti-Spaccamela, Alberto; Crama, Yves ULg; Goossens, Dries et al

Book published by KU Leuven (2015)

This volume contains abstracts of talks presented at the 12th Workshop on Models and Algorithms for Planning and Scheduling Problems (MAPSP 2015), held from June 8 to June 12, 2015, in La Roche-en-Ardenne ... [more ▼]

This volume contains abstracts of talks presented at the 12th Workshop on Models and Algorithms for Planning and Scheduling Problems (MAPSP 2015), held from June 8 to June 12, 2015, in La Roche-en-Ardenne, Belgium. MAPSP is a biennial workshop dedicated to all theoretical and practical aspects of scheduling, planning, and timetabling. The abstracts in this volume include 5 invited talks by Onno Boxma, Michel Goemans, Willem-Jan van Hoeve, Rolf Niedermeier, and Stephan Westphal, plus 88 contributed talks. [less ▲]

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See detailWhat the heck is Revenue Management
Lurkin, Virginie ULg; Schyns, Michael ULg; Garrow, Laurie

Scientific conference (2015, May 08)

The airline industry changed dramatically in 1978 when it became deregulated. Operations research analysts played a critical role after deregulation by developing algorithms and decision-support systems ... [more ▼]

The airline industry changed dramatically in 1978 when it became deregulated. Operations research analysts played a critical role after deregulation by developing algorithms and decision-support systems designed to help airlines to maximize their revenue. More than thirty-five years after deregulation, the airline industry is faced with new challenges. The increased use of the Internet as the major distribution channel and the increased market penetration of low cost carriers have led to an increasing interest in using discrete choice models to model air travel demand as the collection of individual's decisions. [less ▲]

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See detailWhat is the impact of ticket-level fare information on classic itinerary choice models ?
Lurkin, Virginie ULg; Garrow, Laurie; Schyns, Michael ULg

Scientific conference (2015, March 25)

I have been invited by Prof. Dr. Catherine Cleophas as an external guest to the "Revenue Management Colloquium" in Aix-la-Chapelle from March 25 to March 26. The aim is to present my own doctoral project ... [more ▼]

I have been invited by Prof. Dr. Catherine Cleophas as an external guest to the "Revenue Management Colloquium" in Aix-la-Chapelle from March 25 to March 26. The aim is to present my own doctoral project and discuss the presentations of other PhD students [less ▲]

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See detailEarly detection of university students in potential difficulty
Hoffait, Anne-Sophie ULg; Schyns, Michael ULg

Conference (2015, February)

Rate of success in the first year at University in Belgium is very low regarding other foreign universities. The University of Liege, as other Universities, has already taken different initiatives. But by ... [more ▼]

Rate of success in the first year at University in Belgium is very low regarding other foreign universities. The University of Liege, as other Universities, has already taken different initiatives. But by early identifying students who have a high probability to face difficulties if nothing is done, the Universities might develop adapted methods to attack the problem with more emphasis where it is more needed and when it is still possible. Thus we want to develop a decision tool able to identify these students to help them. For that, we consider three standard datamining methods: logistic regression, artificial neural networks and decision trees and focus on early detection, i.e. before starting at the University. Then, we suggest to adapt these three methods as well as the classification framework in order to increase the probability of correct identification of the students. In our approach, we do not restrict the classification to two extreme classes, e.g. failure or success, but we create subcategories for different levels of confidence: high risk of failure, risk of failure, expected success or high probability of success. The algorithms are modified accordingly and to give more weight to the class that really matters. Note that this approach remains valid for any other classification problems for which the focus is on some extreme classes; e.g. fraud detection, credit default... Finally, simulations are conducted to measure the performances of the three methods, with and without the suggested adaptation. We check if the factors of success/failure we can identify are similar to those reported in the literature. We also make a ``what-if sensitivity analysis''. The goal is to measure in more depth the impact of some factors and the impact of some solutions, e.g., a complementary training or a reorientation. [less ▲]

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See detailDoc'Data: mesure de la persévérance au doctorat à l'Université de Liège
Aerts, Stéphanie ULg; Haesbroeck, Gentiane ULg; Schyns, Michael ULg

Report (2015)

Le Conseil du Doctorat a parmi ses missions celle d’accompagner les doctorants dans leur parcours et de mettre en place des actions en vue de favoriser la réussite. Cependant, pour réellement mesurer ... [more ▼]

Le Conseil du Doctorat a parmi ses missions celle d’accompagner les doctorants dans leur parcours et de mettre en place des actions en vue de favoriser la réussite. Cependant, pour réellement mesurer l’impact des actions mises en oeuvre dans cette optique, il faut d’abord pouvoir quantifier le taux de réussite. Or, mesurer le taux de réussite dans les études de 3ème cycle n’est pas une démarche évidente. De nombreux raccourcis de raisonnement sont tentants mais mènent à des résultats très variables et incorrects. Le but de ce document est de présenter les difficultés inhérentes au calcul d’un taux de réussite et de proposer quelques procédures appropriées. Dans un premier temps, les chances (ou, d’un point de vue plus formel, les probabilités) de réussite et d'abandon des doctorants sont modélisées en fonction du nombre d’années d’inscription et en tenant compte de caractéristiques du doctorant comme son genre, sa nationalité, son âge au moment de l’inscription, son statut professionnel... L'analyse descriptive et exploratoire est ensuite confirmée par l’application d’une analyse de survie avec risques compétitifs. [less ▲]

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Peer Reviewed
See detailThe Airline Container Loading Problem with Pickup and Delivery
Lurkin, Virginie ULg; Schyns, Michael ULg

Conference (2014, November 09)

We address the problem of allocating containers into predefined positions of a carrier, in this case aircraft, under several realistic structural and safety constraints. The originality of our approach is ... [more ▼]

We address the problem of allocating containers into predefined positions of a carrier, in this case aircraft, under several realistic structural and safety constraints. The originality of our approach is to allow multi-trips with pickup and delivery at some intermediate locations. The objective is to minimize the economic and environmental costs including the impact of the intermediate operations. We resort to an integer linear model. Numerical experiments have been performed using a standard B\&C library. Heuristics are developed to speed up the process. [less ▲]

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See detailEarly detection of university students in potential difficulty : a case study
Hoffait, Anne-Sophie ULg; Schyns, Michael ULg

Conference (2014, November)

Rate of success in the first year at University in Belgium is very low regarding other foreign universities. The University of Liege, as other Universities, has already taken different initiatives. But by ... [more ▼]

Rate of success in the first year at University in Belgium is very low regarding other foreign universities. The University of Liege, as other Universities, has already taken different initiatives. But by early identifying students who have a high probability to face difficulties if nothing is done, the Universities might develop adapted methods to attack the problem with more emphasis where it is more needed and when it is still possible. Thus we want to develop a decision tool able to identify these students to help them. For that, we consider three standard datamining methods: logistic regression, artificial neural networks and decision trees and focus on early detection, i.e. before starting at the University. Then, we suggest to adapt these three methods as well as the classification framework in order to increase the probability of correct identification of the students. In our approach, we do not restrict the classification to two extreme classes, e.g. failure or success, but we create subcategories for different levels of confidence: high risk of failure, risk of failure, expected success or high probability of success. The algorithms are modified accordingly and to give more weight to the class that really matters. Note that this approach remains valid for any other classification problems for which the focus is on some extreme classes; e.g. fraud detection, credit default... Finally, simulations are conducted to measure the performances of the three methods, with and without the suggested adaptation. We check if the factors of success/failure we can identify are similar to those reported in the literature. We also make a ``what-if sensitivity analysis''. The goal is to measure in more depth the impact of some factors and the impact of some solutions, e.g., a complementary training or a reorientation. [less ▲]

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See detailThe Airline Container Loading Problem with Pickup and Delivery
Lurkin, Virginie ULg; Schyns, Michael ULg

in Airline Group of the Intl Federation of Operational Research Soc ( AGIFORS ) (Ed.) 54th AGIFORS Annual Proceedings 2014 (2014, October 19)

The present paper looks into the problem of optimizing the loading of a set of containers and pallets into cargo aircraft serving multiple airports. Due to the pickup and delivery operations occurring at ... [more ▼]

The present paper looks into the problem of optimizing the loading of a set of containers and pallets into cargo aircraft serving multiple airports. Due to the pickup and delivery operations occurring at intermediate airports, this problem is simultaneously a weight and balance problem and a sequencing problem. Our objective is to minimize fuel and handling operations costs. This problem is shown to be NP-hard. We resort to a mixed integer linear program. On the basis of a professional partner's real-world data, TNT Airways, we perform numerical experiments using a standard B&C library. This approach yields better solutions than traditional manual planning, which results in substantial cost savings. [less ▲]

Detailed reference viewed: 67 (14 ULg)