 
Summary: Reformulation of capacitated facility location problems:
How redundant information can help
Karen Aardal \Lambda
Department of Computer Science
Utrecht University
P.O. Box 80089
3508 TB Utrecht, The Netherlands
aardal@cs.ruu.nl
In memory of š Asa
Abstract
Most facility location problems are computationally hard to solve. The standard technique
for solving these problems is branchandbound. To keep the size of the branchandbound tree
as small as possible it is important to obtain a good lower bound on the optimal solution by
deriving strong linear relaxations. One way of strengthening the linear relaxation is by adding
inequalities that define facets of the convex hull of feasible solutions. Here we describe some
simple, but computationally very useful classes of inequalities that were originally developed
for relaxations of the facility location problems. Algorithms for generating violated inequalities
belonging to the described classes have been implemented as system features in various branch
andbound software packages, so as long as the software can recognize the relaxations for
which the inequalities are developed, the inequalities will be generated ``automatically''. Here
