References of "Schyns, Michael"
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See detailEarly Detection of University Students with Potential Difficulties
Hoffait, Anne-Sophie ULiege; Schyns, Michael ULiege

in Decision Support Systems (2017), 101

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. We adapt three data mining methods, namely random forest, logistic regression and artificial neural network algorithms. We design algorithms to increase the accuracy of the prediction when some classes are of major interest. These algorithms are context independent and can be used in different fields. Real data pertaining to undergraduates at the University of Liège (Belgium), illustrates our methodology. [less ▲]

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See detailMIP-based constructive heuristics for the three-dimensional Bin Packing Problem with transportation constraints
Paquay, Célia ULiege; Limbourg, Sabine ULiege; Schyns, Michael ULiege et al

in International Journal of Production Research (2017)

This article is about seeking a good feasible solution in a reasonable amount of computation time to the three-dimensional Multiple Bin Size Bin Packing Problem (MBSBPP). The MBSBPP studied considers ... [more ▼]

This article is about seeking a good feasible solution in a reasonable amount of computation time to the three-dimensional Multiple Bin Size Bin Packing Problem (MBSBPP). The MBSBPP studied considers additional constraints encountered in real world air transportation situations, such as cargo stability and the particular shape of containers. This MBSBPP has already been formulated as a Mixed Integer linear Programming problem, but as yet only poor results have been achieved for even fairly small problem sizes. The goal of the work this paper describes is to develop heuristics that are able to quickly provide good initial feasible solutions for the MBSBPP. Three methodologies are considered, which are based on the decomposition of the original problem into easier subproblems: the matheuristics Relax-and-Fix, Insert-and-Fix and Fractional Relax-and-Fix. They have been parametrised on real data sets and then compared to each other. In particular, two of these techniques show promising results in reasonable computational times. [less ▲]

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See detailEarly detection of university students with potential difficulties
Hoffait, Anne-Sophie ULiege; Schyns, Michael ULiege

Conference (2017, July)

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. We aim at early detection of ... [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. 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. We adapt three data mining methods, namely random forest, logistic regression and artificial neural network algorithms. We design algorithms to increase the accuracy of the prediction when some classes are of major interest. These algorithms are context independent and can be used in different fields. They rely on a dynamic split of the observations into subclasses during the training process, so as to maximize an accuracy criterion. Four classes are so built: high risk of failure, risk of failure, expected success or high probability of success. Real data pertaining to undergraduates at the University of Liège (Belgium), illustrates our methodology. With our approach, we are now able to identify with a high rate of confidence (90%) a subset of 12.2% of students facing a very high risk of failure, almost the quadruple of those identified with a non-dynamic approach. By testing some confidence levels, our approach makes it possible to rank the students by levels of risk and a sensitivity analysis allows us to find out why some students are likely to encounter difficulties. [less ▲]

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

in Transportation Research. Part A : Policy & Practice (2017), 100

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 detailA best fit heuristic for the three-dimensional Bin Packing Problem with practical constraints from an air transportation application
Paquay, Célia ULiege; Limbourg, Sabine ULiege; Schyns, Michael ULiege

in Proceedings of the BIVEC-GIBET Transport Research Days 2017 (2017)

This work considers the three-dimensional Multiple Bin Size Bin Packing Problem which consists in packing a set of cuboid boxes into containers of various shapes, while minimising unused space. The aim of ... [more ▼]

This work considers the three-dimensional Multiple Bin Size Bin Packing Problem which consists in packing a set of cuboid boxes into containers of various shapes, while minimising unused space. The aim of the present work is to find good initial solutions in short computational times. In this purpose, a fast best fit heuristic able to manage the different constraints to be met in transportation is developed. The heuristic is split into two distinct phases. The first phase deals with the packing of boxes into identical bins using an extension of the Extreme Points rule. During this phase, the fragility, stability and orientation of the boxes are taken into account, as well as the special shape of the bins and their weight capacity. The second phase considers the multiple types of available bins. If necessary, the best loading pattern identified is enhanced with respect to weight distribution in post processing. After parametrisation, computational experiments are performed on data sets specially designed for this application. The heuristic requires very short computational times to achieve promising results. [less ▲]

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See detailInstances for the 3D Multiple Bin Size Bin Packing Problem
Paquay, Célia ULiege; Limbourg, Sabine ULiege; Schyns, Michael ULiege

Textual, factual or bibliographical database (2017)

The subject of this work is to solve the problem of packing a set of shipments (various cuboid boxes) into containers of various shapes without wasting loading space. All the boxes have to be loaded and ... [more ▼]

The subject of this work is to solve the problem of packing a set of shipments (various cuboid boxes) into containers of various shapes without wasting loading space. All the boxes have to be loaded and few are identical. As it is the case for all the packing problems, the packing has to satisfy geometry constraints: the items cannot overlap and have to lie entirely inside the bins. The richness of our application is to manage additional and common constraints: the bin weight capacity, the rotations of the boxes, the stability and the fragility of the boxes and the uniformity of the weight distribution inside the ULDs. The last constraint is crucial in air transportation: when ULDs are packed inside the airplane, the centre of gravity is computed assuming each ULD has a centre of gravity close to the geometrical centre of its basis. This type of constraints can be adapted to road transportation for the axle weight limits, which plays a key role since the weigh-in-motion systems become more common. [less ▲]

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See detailA tailored two-phase constructive heuristic for the three-dimensional Multiple Bin Size Bin Packing Problem with transportation constraints
Paquay, Célia ULiege; Limbourg, Sabine ULiege; Schyns, Michael ULiege

E-print/Working paper (2017)

This paper considers the three-dimensional Multiple Bin Size Bin Packing Problem which consists in packing a set of cuboid boxes into containers of various shapes with minimising unused space. The problem ... [more ▼]

This paper considers the three-dimensional Multiple Bin Size Bin Packing Problem which consists in packing a set of cuboid boxes into containers of various shapes with minimising unused space. The problem is extended to air cargo where bins are Unit Load Devices, especially designed for fitting in aircraft. We developed a fast constructive heuristic able to manage the different constraints met in transportation. The heuristic is split into two distinct phases. The first phase deals with the packing of boxes into identical bins using an extension of the Extreme Points. During this phase, the fragility, stability and orientations of the boxes are taken into account as well as the special shape of the bins and their weight capacity. The second phase takes into account the multiple types of available bins. If necessary, the best found loading pattern is finally enhanced with respect to weight distribution in a post processing. After parametrisation, computational experiments have been performed on data sets especially designed for this application. The heuristic requires really short computational times to achieve promising results. [less ▲]

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

Conference (2016, July)

Detailed reference viewed: 48 (5 ULiège)
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See detailAccounting for price endogeneity in airline itinerary choice models
Lurkin, Virginie ULiege; 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 ▲]

Detailed reference viewed: 54 (5 ULiège)
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See detailEarly Detection of University Students in Potential Difficulty
Hoffait, Anne-Sophie ULiege; Schyns, Michael ULiege

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 ULiege; 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 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 ULiege; 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 ULiege; Schyns, Michael ULiege; Limbourg, Sabine ULiege

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 ULiege

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 ULiege; 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 ULiege; Schyns, Michael ULiege

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 ULiege; 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 ▲]

Detailed reference viewed: 178 (8 ULiège)
See detailWhat the heck is Revenue Management
Lurkin, Virginie ULiege; Schyns, Michael ULiege; 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 ULiege; Garrow, Laurie; Schyns, Michael ULiege

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 ▲]

Detailed reference viewed: 92 (4 ULiège)