We also develop a Lagrangean decomposition based heuristic. The subproblems
from the decomposition have a special structure. One of the subproblems is the multi-
facility lot-sizing problem that we study in detail in Chapter 2. The multi-facility
lot-sizing problem is an extension of the economic lot-sizing problem. We add a new
dimension to the classical problem, the facility selection decision. We provide the
following heuristic approaches to solve this problem: dynamic programming, a primal-
dual method, a cutting plane method and a linear programming based algorithm. We
propose a set of valid inequalities and show that they are facet defining. We tested
the performance of the heuristics on a wide range of randomly generated problems.