Technical Sessions – Monday July 11

TB-07 IFORS 2011 - Melbourne
cedex 3, France, Pierre.Dejax@emn.fr, Hugues Dubedout,
Thomas Yeung
Real-life IRPs are often subject to uncertainties such as customer demand and
supply disruption. In order to deal with these uncertainties, robust solutions
are often proposed. To that aim, we propose a methodology consisting of the
1. scenario generation to model the uncertainties, 2. obtaining robust IRP
solutions from custom heuristics, and 3. evaluation of the impact of the different
uncertainties on the robust solutions. This methodology was tested on
both simulated test-cases and real-life problems as encountered in cryogenic
gas distribution at Air Liquide.
� TB-07
Tuesday, 11:00-12:30
Meeting Room 106
Discrete Optimisation
Stream: Discrete Optimisation
Invited session
Chair: François Vanderbeck, Institut de Mathématiques de Bordeaux,
Université Bordeaux1 & INRIA Bordeaux, 351 cours de la
Libération, F-33405, Talence- CEDEX, France,
fv@math.u-bordeaux1.fr
1 - Bi-dynamic Constraint Aggregation and Subproblem
Reduction for Crew Pairing Problem
Francois Soumis, GERAD, 3000 Cote Ste-Catherine, H3T 2A7,
Montreal, Québec, Canada, francois.soumis@gerad.ca,
Mohammed Saddoune, Issmail Elhallaoui, Guy Desaulniers
Bi-dynamic constraint aggregation is a new approach introduced to speed up
the column generation method when solving degenerate set partitionig problems.
The agregation profits from degeneracy to reduce the size of the master
problem. The subproblems reduction eliminates arcs with less promising
marginal costs. This reduces significantly the number of column generation iterations
when we start from a good heuristic solution. These reductions lead to
big savings in solution time. Tests on some hard real life crew pairing problems
will be presented with the trivial initial solution: "follow the aircraft" and with
an initial solution obtained with a linear programing approximation.
2 - Large Sized Extended Formulations for Routing and
Scheduling Problems
Eduardo Uchoa, Engenharia de Produção, Universidade Federal
Fluminense, Rua Passo da Pátria 156, São Domingos,
22430-210, Niterói, Rio de Janeiro, Brazil,
uchoa@producao.uff.br, Artur Pessoa, Marcus Poggi de Aragão,
Rosiane de Freitas Rodrigues, Lorenza Moreno
We present an extended formulation that allow viewing and parallel machine
scheduling and capacitated vehicle routing problems in a very similar way:
the machines correspond to the vehicles, jobs to the clients, and the processing
times to client demands. This means that known VRP cuts can be effectively
used in those scheduling problems and vice versa. However, the pseudopolynomially
large size of the formulation requires a sophisticated branch-cutand-price
implementation. Computational results show good results in comparison
with other known methods
3 - Using the Cost Splitting Dual for Multiple Resource
Constrained Shortest Path Problems
Olivia Smith, Mathematics and Statistics, University of
Melbourne, 3052, Parkville, Vic, Australia,
livsmith21@gmail.com, Natashia Boland
Shortest path problems with a single resource constraint are much easier to
solve than problems where there are many resource constraints. This makes decomposition
approaches attractive as they can exploit the easier problem structure.
We explore a reformulation in which we define a set of variables for each
resource with extra constraints enforcing the equality of these variables. Relaxing
these constraints in a Lagrangean fashion leads to a dual known as the Cost
Splitting Dual. We investigate the use of this dual to assist in preprocessing and
solving the multiple resource problem.
4 - Numerical Experiments with Column Generation for Extended
Formulations
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François Vanderbeck, Institut de Mathématiques de Bordeaux,
Université Bordeaux1 & INRIA Bordeaux, 351 cours de la
Libération, F-33405, Talence- CEDEX, France,
fv@math.u-bordeaux1.fr
Extended formulations for integer programs are often tight but too large for
a direct treatment. When they stem from a decomposition principle, a hybrid
column generation procedure applies that mimics that for the Dantzig-Wolfe
reformulation. Pricing subproblem solutions can be expressed in the extended
space and added to the current restricted formulation along constraints that become
active. Such “column-and-row generation” has a comparative advantage
over standard column generation: in the extended space, subproblem solutions
can be recombined resulting in faster convergence.
� TB-08
Tuesday, 11:00-12:30
Meeting Room 107
Health Care Operations II
Stream: Service & Health Care Operations
Invited session
Chair: Karen Smilowitz, Industrial Engineering and Management
Sciences, Northwestern University, 2145 Sheridan Road,
Technological Institute M233, 60208-3119, Evanston, Illinois, United
States, ksmilowitz@northwestern.edu
1 - Improving Access to Community-based Chronic Care
through Improved Capacity Allocation
Karen Smilowitz, Industrial Engineering and Management
Sciences, Northwestern University, 2145 Sheridan Road,
Technological Institute M233, 60208-3119, Evanston, Illinois,
United States, ksmilowitz@northwestern.edu, Sarang Deo,
Seyed Iravani
Most health care operation models focus either on efficiency improvements in
the delivery system or improvements in clinical decisions. We consider a novel
setting of community-based delivery of chronic asthma care, where it is necessary
to integrate these two approaches. We develop and analyze a joint disease
progression and capacity allocation model to investigate how operational decisions
can improve population level health outcomes. We test our findings using
data provided by Mobile C.A.R.E, a community-based provider of asthma care
to public school students in Chicago.
2 - Role of Flexibility in Managing Operating Room Resources
in Hospitals
Kannan Sethuraman, Melbourne Business School, 3441
Woodcliff Road, Melbourne, Australia,
K.Sethuraman@mbs.edu, Devanath Tirupati
We examine the role of flexibility in managing operating room resources in a
tertiary hospital providing elective surgeries in a variety of specialties. We consider
two kinds of flexibility and develop a queueing theoretic stochastic model
based on approximations that is useful for a preliminary analysis to assess the
impact of alternative strategies. The analytic model is complemented by a simulation
model to provide detailed performance evaluation. Managerial insights
are derived from computational results based on representative data from a real
life case study.
3 - Drivers of Excellence in Veterans’ Administration Clinics
Subramaniam Ramanarayanan, Anderson School of
Management, UCLA, 90403, Los Angeles, CA, United States,
subbu@anderson.ucla.edu, Kumar Rajaram
Although there is clear consensus about a demonstrable need for improvement
of outcomes such as access, wait times and quality in healthcare, there is little
clarity about how this might be achieved. While there is a significant amount of
research focused on the impact of external structural forces on outcomes, our
understanding of the importance of various intra-organizational characteristics
in determining outcomes is still fairly limited. We address this research gap by
focusing on the structural determinants of outcomes in a sample of Veteran’s
Administration Clinics in the US.