We study a multi-item, two-echelon, continuous-review inventory problem at a Dutch utility company, Liander. We develop a model that optimizes the quantities of service parts and their allocation in the two-echelon network under an aggregate waiting time restriction. Specific aspects that we address are emergency shipments in case of stockout, and batching for regular replenishment orders at th...

The integrated crew scheduling (ICS) problem consists of determining, for a set of available crew members, least-cost schedules that cover all flights and respect various safety and collective agreement rules. A schedule is a sequence of pairings interspersed by rest periods that may contain days off. A pairing is a sequence of flights, connections, and rests starting and ending at the same cre...

Tail Assignment is the problem of assigning flight legs to aircraft while satisfying all operational constraints, and optimizing some objective function. In this article, we present a hybrid column generation and constraint programming solution approach. This approach can be used to quickly produce solutions for operations management, and also to produce close-to-optimal solutions for long and ...

The Capacitated p-median problem (CPMP) seeks to solve the optimal location of p facilities, considering distances and capacities for the service to be given by each median. In this paper we present a column generation approach to CPMP. The identified restricted master problem optimizes the covering of 1-median clusters satisfying the capacity constraints, and new columns are generated consider...

Dual-head placement machines are important in the assembly of circuit cards because they offer the capability to place large components accurately. This paper presents a novel column-generation approach for optimizing the placement operations of a dual-head placement machine with the ultimate goal of improving the efficiency of assembly operations. Research objectives are a model that reflects ...

Column generation techniques have become a widely used technique to successfully solve large (integer) linear programs. One of the keys to obtaining a practically efficient algorithm is to have a fast method to limit the pricing of new columns to a small set. We study a large scale real-world vehicle dispatching problem with soft time windows which can be modeled as an integer linear program of...

We introduce a new approach to tracking a large number of objects. Specifically we consider tracking in the context of higher order Markov interactions which can not be modeled using network flow techniques as currently developed. Our approach relies on delayed column generation and is inspired by the corresponding approach to the cutting stock problem. Columns can be generated exactly using dy...

In this paper we propose a branch, price and remember algorithm to solve the U shaped assembly line balancing problem. Our proposed algorithm uses a column generation approach to obtain tight lower bounds. It also uses a modification of Hoffman algorithm to obtain high quality upper bounds. Memory is also used in our proposed algorithm to store generated columns to enhance the speed of column g...

This paper presents our investigations on a hybrid constraint programming based column generation (CP-CG) approach to nurse rostering problems. We present a complete model to formulate all the complex real-world constraints in several benchmark nurse rostering problems. The hybrid CP-CG approach is featured with not only the effective relaxation and optimality reasoning of linear programming bu...

We propose a new decomposition model and a multi-column generation algorithm for solving the Locomotive Assignment Problem (LAP). The decomposition scheme relies on consist configurations, where each configuration is made of a set of trains pulled by the same set of locomotives. We use the concept of conflict graphs in order to reduce the number of trains to be considered in each consist config...