Technical Sessions – Monday July 11

TA-06 IFORS 2011 - Melbourne
� TA-06
Tuesday, 9:00-10:30
Meeting Room 105
Workforce Management in Vehicle Routing
Stream: Transportation
Invited session
Chair: Maciek Nowak, Information Systems and Operations
Management, Loyola University Chicago, 1 E. Pearson Ave., 60611,
Chicago, IL, United States, mnowak4@luc.edu
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 - Workforce Management in Periodic Routing: Lessons
Learned on a UPS Package Car
Karen Smilowitz, Industrial Engineering and Management
Sciences, Northwestern University, 2145 Sheridan Road,
Technological Institute M233, 60208-3119, Evanston, Illinois,
United States, ksmilowitz@northwestern.edu, Maciek Nowak
Service quality and driver efficiency in delivery operations may be enhanced
by increasing the regularity with which drivers visit customers. However, such
consideration can increase travel distance. In this talk, we discuss how workforce
management impacts periodic routing decisions. We review the treatment
of workforce management in routing models from the academic literature and
commercial software.
2 - Impact of Consistency of Care on Home Healthcare
Routing
Maciek Nowak, Information Systems and Operations
Management, Loyola University Chicago, 1 E. Pearson Ave.,
60611, Chicago, IL, United States, mnowak4@luc.edu, Mike
Hewitt, Ashlea Bennett
For some organizations, cost is one of many factors used to measure the quality
of a route. In home health care, consistency with respect to the nurse that visits
a patient or the time of day a patient is visited can be just as important. Also,
advances in information technology devices provide a new method for providing
care. We present an integer programming model with multiple objectives
to study these conjoined factors and the impact devices have on the ability to
achieve them.
3 - The Value of a Priori and Partial Information for Probabilistic
Vehicle Routing
Richard Wong, United Parcel Service, 2311 York Road, 21093,
Timonium, Maryland, Afghanistan, rtwong@ups.com, Si Chen,
Hongsheng Zhong
Phase I considers a probabilistic vehicle routing problem with route duration
constraints. In phase II, customer locations are gradually revealed but adjusting
a customer’s phase I assignment incurs a penalty. This problem arises in
several logistics contexts including small package delivery. We present models
and computational results evaluating operating/optimization strategies for
balancing workloads under varying amounts of partial information.
� TA-07
Tuesday, 9:00-10:30
Meeting Room 106
Flow Problems - Easy, Hard, and (almost)
Impossible
Stream: Discrete Optimisation
Invited session
Chair: Gregor Pardella, University of Cologne, Pohligstr. 1, 50969,
Cologne, Germany, pardella@informatik.uni-koeln.de
Chair: Birgit Engels, AFS, University of Cologne, Weyertal 80,
50931, Cologne, NRW, Germany, engels@zpr.uni-koeln.de
32
1 - Preprocessing Strategies for Max-Flow on Structured
Graphs
Gregor Pardella, University of Cologne, Pohligstr. 1, 50969,
Cologne, Germany, pardella@informatik.uni-koeln.de, Frauke
Liers
Max-flow problems occur in a wide range of applications and, although already
well-studied and equipped with fast implementations, they are still an
area of active ongoing research. Motivated by the physics application of socalled
random field Ising models we introduce flow conserving shrinking rules.
Additionally we present a hybrid max-flow algorithm that finds a good initial
solution and then extends this to the optimum. The considered graphs are structured
in the sense that a larger set of nodes is either connected to the source or
the sink. This is joint work with Frauke Liers.
2 - Matching under an Edge-Disjoint-Paths Constraint
Birgit Engels, AFS, University of Cologne, Weyertal 80, 50931,
Cologne, NRW, Germany, engels@zpr.uni-koeln.de
We introduce a constrained matching problem (MEDP) on a graph G=(V,E)
and a ’constraint’ graph C whose node set contains V. Then (MEDP) is solved
by a matching M in G of maximal cardinality, such that C contains a set P(M)
of edge-disjoint paths between all pairs u,v with (u,v) in M. We use M to round
a half-integral minimal cost generalized flow with minimal constraint violation
in an application-oriented setting. For general C and |M|>2 the constraint is NPhard
to check. We present a polynomial time dynamic programming algorithm
to solve (MEDP) optimally if C is a tree.
3 - Integer Multicommodity Flows in Graph Drawing
Daniel Schmidt, Computer Science, University of Cologne,
Germany, schmidt@informatik.uni-koeln.de, Michael Juenger
The maximum planar subgraph problem asks for a subgraph of a given graph G
that is planar and has maximum weight. This problem is NP hard, but the polytope
P of incidence vectors of planar subgraphs of G is well-studied: It turns
out that subdivisions of the k33 or the k5 induce facet defining inequalities of P.
This allows for a branch and cut approach in which we look for subdivisions of
k33 of minimum weight w.r.t. a lp solution in the cutting step. So far, this could
only be done heuristically. We propose an exact separation algorithm based on
integer multicommodity flows.
� TA-08
Tuesday, 9:00-10:30
Meeting Room 107
Health Care Operations I
Stream: Service & Health Care Operations
Invited session
Chair: Christiane Barz, UCLA Anderson School of Management,
110 Westwood Plaza, B520 Gold Hall, 90095, Los Angeles,
California, United States, cbarz@anderson.ucla.edu
1 - Minimizing the Waiting Time for Emergency Surgery
Theresia van Essen, Discrete Mathematics and Mathematical
Programming, University of Twente, P.O. Box 217, 7500 AE,
Enschede, Netherlands, j.t.vanessen@ewi.utwente.nl
Emergency surgeries should be scheduled as quick as possible to reduce complications
and morbidity. The waiting time of emergency surgeries can be reduced
by scheduling them in one of the elective operating rooms instead of
an emergency operating room. The emergency patients are operated once an
ongoing elective surgery is finished. These moments in time are denoted by
’break-in-moments’ (BIMs). By spreading the BIMs as evenly as possible over
the day, the waiting time of emergency surgeries can be reduced even further.
In this presentation, we discuss several solution methods for the off-line and
on-line version of this BIM optimization problem.
2 - Managing Limited Bed Capacity of a Hospital
Burhaneddin Sandikci, Booth School of Business, University of
Chicago, 5807 South Woodlawn Avenue, 60637, Chicago, IL,
United States, burhan@chicagobooth.edu, Don Eisenstein, Tom
Best, David Meltzer