We study two different lot-sizing problems with time windows that have been proposed recently. For the case of production time windows, in which each client specific order must be produced within a given time interval, we derive tight extended formulations for both the constant capacity and...

We consider here the mixing set with flows: s + xt amp;#8805; bt, xt amp;#8804; yt for 1 amp;#8804; t amp;#8804; n; s E IR, x E IR, y E Z. It models the flow version of the basic mixing set introduced and studied by Guuml;nluuml;k and Pochet, as well as the most simple stochastic lot-sizing problem with...

We consider a multi-item lot-sizing problem in which there are demands, and unit production and storage costs. In addition production of any mix of items is measured in batches of fixed size, and there is a fixed set-up cost per batch in each period. Suppose that the unit production costs are...

We consider mixed-integer sets of the type MIX TU = {x : Ax amp;#8805; b; xi integer, i amp;#8712; I}, where A is a totally unimodular matrix, b is an arbitrary vector and I is a nonempty subset of the column indices of A. We show that the problem of checking nonemptiness of a set MIX TU is NP-complete...

For the problem of lot-sizing on a tree with constant capacities, or stochastic lot-sizing with a scenario tree, we present various reformulations based on mixing sets. We also show how earlier results for uncapacitated problems involving (Q, SQ) inequalities can be simplified and extended....

Much progress has been made in recent years in solving certain classes of production planning problems using mixed integer programming. One of the major challenges is how to make this expertise available and easy to use to the non-specialist and to the practitioners. Here we describe a modeling...