Luc Muyldermans

A guided local search heuristic for the capacitated arc routing problem

Abstract This paper presents a new local search algorithm for the capacitated arc routing problem (CARP). The procedure uses single vehicle moves and moves that operate on two routes, both derived from a node routing context but properly adapted to work well for arc routing problems. We combine the algorithm with the meta-heuristic guided local search and further use the mechanisms of neighbor lists and edge marking to improve the solution quality and to save computation time. Experiments on standard benchmark problems from the literature show that our algorithm outperforms the existing heuristics for the CARP. On a set of new test problems, the local search approach consistently produces high quality solutions and often detects an optimal solution within limited computation time.

Hewlett-Packard Company Unlocks the Value Potential from Time-Sensitive Returns

Hewlett-Packard (HP) and other companies producing short life-cycle products with rapid value erosion squander the opportunity to profit from returned time-sensitive products when they treat them as a nuisance. Instead of focusing on cost minimization and technical quality, they should recognize returns as a value stream and maximize the revenue from smart and fast disposition, proper refurbishment, and prompt resale through the appropriate channels. We worked on a project with Hewlett-Packards remarketing group to unlock the value potential of time-sensitive returns. We analyzed data using simple calculations to reveal the major drivers and magnitude of potential value recovery, and we used simple operations research flow models to evaluate new design and policy options for the reverse supply chain. HP benefited from an integrated end-to-end business approach to product returns.

Districting for salt spreading operations

Abstract The districting problem presented in this paper involves the partitioning of the road network in a region into sub-networks (or districts), to facilitate the organization of the operations to be performed within the region. Typically, each district contains one local center (depot) whose location is given, while the operations involve different types of routing, with routes starting and ending at the depot. For public sector applications like salt spreading and road maintenance, this partitioning is a real distinct stage in the organization and planning of services, and as is the case with location, districting is of a non-operational nature. Relevant characteristics of well-designed districts are: ability to support good routing, balance in workload, compactness of the sub-areas, centrality of the depot, etc. We present a heuristic procedure for our districting problem. First we partition the road network into small cycles, then we aggregate them into districts in two phases. Phase 1 uses an approach based on bin packing principles, while in Phase 2 a multi criteria approach is used. We illustrate the procedure and discuss its merits for the salt spreading operations in the province of Antwerp.

Brachial, radial, or femoral approach for elective Palmaz-Schatz stent implantation: A randomized comparison

UNLABELLED From October 1994 to November 1995, 150 male eligible patients were randomly assigned to Palmaz-Schatz stent implantation through 6 French catheters using the femoral (puncture) (n = 56), radial (puncture) (n = 56), or brachial (cutdown) (n = 38) approach at 6 participating Belgian centers. Acenocoumarol was given for 1 month after stenting. END POINTS Primary-entry site complications (bleeding, haematoma, transfusion, occlusion, surgery) poststent implantation. Secondary-success rate, stent thrombosis, Q or non Q wave MI, repeat PTCA, CABG, CVA, haemorrage, death. There were no statistically significant differences between the three groups for base line and angiographic patient characteristics, procedural characteristics, in hospital outcome, average hospitalisation time after stenting, events during the month after stenting, or local complications at 1 month follow-up. The only statistically significant difference was the arterial time of the procedure: mean +/- SD (minutes) brachial 31.0 +/- 10.02 *P < 0.001, femoral 42.2 +/- 21.8, radial 55.8 +/- 31.3 **P < 0.0001 (*brachial vs. femoral, **brachial vs. radial). There was a clear trend toward more technical difficulties and more problems with the radial approach. In each group: vascular surgery at entry site: 0%, blood transfusion: 0%. In our study, local complications and length of hospital stay were similar with the three possible approaches, and brachial approach was associated with a shorter arterial time.

On the benefits of co-collection: Experiments with a multi-compartment vehicle routing algorithm

The Multi-Compartment Vehicle Routing Problem involves clients with a demand for different products and vehicles with several compartments to co-transport these commodities. We present a local search procedure that explores well-known moves (2-opt, cross, exchange, relocate), and exploits the mechanisms of neighbour lists and marking to speed up the searches. We combine the procedure with the Guided Local Search meta-heuristic to improve solution quality. Extensive computational results are reported to uncover when co-distribution by vehicles with multiple compartments is better than separate distribution with un-partitioned trucks. Sensitivities in key problem parameters including, client density and location of the depot, vehicle capacity, client demand and number of commodities are investigated.

Impact of environmental regulations on innovation and performance in the UK industrial sector

Purpose – The role of environmental regulations in inducing innovation and improving performance has been studied in the literature. However, there have been no studies in the UK using statistical data. This paper aims to study the links among regulations, innovation and performance in the UK using sector level data.Design/methodology/approach – The paper used structural equation modelling to study the links among the three variables simultaneously.Findings – The analysis indicates that environmental regulations in the UK are significant in improving economic performance of the industrial sectors. They also find that, in the short run, environmental regulations negatively influence innovation, and innovation negatively influences economic performance in these sectors.Practical implications – The results have implications both for policy makers and firms in the UK industrial sector. For policy makers, environmental regulations have generally improved economic performance. For firms, the study shows that su...

District design for arc-routing applications

In this paper we address the problem of district design for the organisation of arc-routing activities. In particular, the focus is on operations like winter gritting and road maintenance. The problem involves how to allocate the road network edges to a set of depots with given locations. The collection of edges assigned to a facility forms a district in which routes have to be designed that start and end at the facility. Apart from the ability to support good arc routing, well-designed districts for road-maintenance operations should have the road network to be serviced connected and should define clear geographical boundaries. We present three districting heuristics and evaluate the quality of the partitions by solving capacitated arc routing problems in the districts, and by comparing the solution values with a multi-depot CARP cutting plane lower bound. Our experiments reveal that based on global information about the distribution system (ie the number of facilities or districts, the average edge demand and the vehicle capacity) and by using simple guidelines, an adequate districting policy may be selected.

Exploring Variants of 2-Opt and 3-Opt for the General Routing Problem

The general routing problem (GRP) is the problem of finding a minimum length tour, visiting a number of specified vertices and edges in an undirected graph. In this paper, we describe how the well-known 2-opt and 3-opt local search procedures for node routing problems can be adapted to solve arc and general routing problems successfully. Two forms of the 2-opt and 3-opt approaches are applied to the GRP. The first version is similar to the conventional approach for the traveling salesman problem; the second version includes a dynamic programming procedure and explores a larger neighborhood at the expense of higher running times. Extensive computational tests, including ones on larger instances than previously reported in the arc routing literature, are performed with variants of both algorithms. In combination with the guided local search metaheuristic and the mechanisms of marking and neighbor lists, the procedures systematically detect optimal or high-quality solutions within limited computation time.

Identifying the underlying structure of demand during promotions

Research highlights? We develop a demand-factor model to explore the structure of demand during promotions. ? Through structural equation modelling we uncover the causal relationships between different factors and sales volume. ? We test the model using data of a leading soft drink manufacturer in the UK. ? Promotional features and seasonality appear to have a strong impact on sales, unlike special days. ? Our approach is flexible and helps in the planning and execution of promotional deals. It is widely recognized that promotions enhance product sales. Other factors such as seasonality, special days, customer preferences and economic factors may also have an impact on demand. Yet, endeavours to model the dependency of demand on various factors are scarce. We develop a conceptual demand-factor model to represent the dependency of demand on these factors. We examine and validate the conceptual model through structural equation modelling, using sales data of a leading soft drink company involved in supply chain collaboration with downstream retailers. We find that promotional and seasonal factors have a large and direct impact on sales, while special days like festivals and bank holidays have limited influence. Our approach is versatile and can assist demand planners in understanding the demand during promotional events, and in the planning and execution of promotional deals.

Price determinants for remanufactured electronic products: a case study on eBay UK

In this paper, we analyse the market determinants of price differentials between new and remanufactured products in Electronics using data on purchases made on eBay UK. The empirical analysis is carried out by means of linear regression methods, which are capable of controlling for the presence of collinearity among the explanatory variables. Our empirical results suggest that the seller reputation, length of warranties, proxies of demand and supply of remanufactured products, duration, end day of product listings as well as the availability of return policies are important determinants of price differentials. Most importantly, we find that the seller identity plays an important role, as our empirical results are predominantly driven by transactions carried out by non-manufacturer-approved vendors.