Speaker
Laurence Wolsey,
Universite catholique de Louvain, CORE and IMMAQ

Abstract
After a brief introduction on single item lot-sizing, we present tight or tighter formulations for a couple of single and multi-item constant capacity lot-sizing variants. We then examine how reformulation results for basic (typically) single-item problems can be used or extended to tackle realistic multi-item, multi-site problems. As a first application we consider a two-level supply chain, namely a multi-item n-period model with production sites and sales areas with production at the sites and transportation to the areas. We demonstrate the effectiveness of a multi-commodity reformulation combined with the use of inequalities for family set-ups when there are capacities at the transportation level. The second application is a multi-item parallel machine model with start-up and/or sequence dependent changeover costs. Here we show how to extend existing valid inequalities and formulations to deal with identical parallel machines. Some limited computational results are presented.

Bio
Laurence Wolsey works at CORE (Center for Operations Research and Econometrics) and is professor of applied mathematics and operations research in the department of Engineering Mathematics of l'Universite catholique de Louvain in Louvain-la-Neuve, Belgium. His main field of research is mixed integer programming, including theory, the development of branch-and-cut systems, and applications in production planning and scheduling and in network design.
He is author of a textbook "Integer Programming" Wiley 1998, as well as joint author with George Nemhauser of "Integer Programming and Combinatorial Optimization",Wiley 1988, and "Production Planning by Mixed Integer Programming" with Y. Pochet, Springer 2006.
Recently he has been particularly interested in the polyhedral structure of simple mixed integer programming sets, in particular mixing sets and their generalizations that have important applications in lot-sizing, and sets arising from two or more rows of a simplex tableau, an area that has been receiving much attention recently.
He has worked closely with groups at BASF (production planning), France Telecom (multiplexer assignment) and DASH (commercial mixed integer programming systems) among others.
He has received    the Orchard-Hays prize in 1988 from the Mathematical Programming Society (with T.J. Van Roy), the Lanchester Prize in 1989 from the Operations Research Society of America (with G.L. Nemhauser), and the EURO Gold Medal in 1994. He was editor-in-chief of the Mathematical Programming journal from 1999-2003.