Johan Maes

Multilevel capacitated lotsizing complexity and LP-based heuristics

Abstract This paper presents the first heuristics capable of solving multilevel lotsizing problems with capacity constraints on more than one level. Moreover, the form of the heuristics is quite general so that they can easily be extended to solve a variety of problems. If one wants to solve these problems on a routine basis in a real environment one needs to find fast and easy algorithms. However, we show that for certain problem classes this is a very difficult task, far more difficult than has been suggested in the literature. For problems with setup times we show that finding a feasible solution is NP-complete. Even without setup times testing for feasibility can be very difficult. Just how time consuming such heuristics must be is demonstrated. This leaves little chance to build fast and easy heuristics except for the most simple cases. Our exploration of the complexity issues points to mathematical programming as a potential source of heuristics for these problems. This paper presents a new and general approach based on rounding an LP solution for the problem without setup times. The methods use different information and patterns evident in the LP solution are explored. The approach is tested on a large set of problems. The main contributions of this paper are the way in which we distinguish between the easy and hard lotsizing problems, the LP-based heuristics and the test set of capacitated multilevel lotsizing problems.

Unravelling the Hrm-Performance Link: Value-Creating and Cost-Increasing Effects of Small Business Hrm

The majority of empirical studies on the HRM-performance link report a positive story. The costs associated with the productivity rise due to high performance work practices (HPWP) have been largely neglected. The purpose of this study is to develop a conceptual framework that maps both the value-enhancing and cost-raising impact of HPWP. In addition, we want to pronounce upon their overall effect on financial performance. To test our model, we rely on a sample of small businesses. Understanding both performance and cost-related effects of the implementation of HPWP is particularly valuable for small businesses since they often lack financial resources to implement HPWP and benefit less from economies of scale compared to their larger counterparts. Study results indicate that although greater use of HPWP is associated with increased productivity, this effect is offset by increased labour costs. However, we find an overall positive effect of HPWP on firm profitability.

LINEAR PROGRAMMING, SIMULATED ANNEALING AND TABU SEARCH HEURISTICS FOR LOTSIZING IN BOTTLENECK ASSEMBLY SYSTEMS

Multilevel lotsizing is one of the most challenging subjects in production planning, especially in the presence of capacity constraints. In this paper we investigate lotsizing heuristics for assembly production systems with a bottleneck. More specifically, we discuss heuristics based on Linear Programming (LP), and compare the performance of these heuristics with the performance of approaches based on simulated annealing and tabu search techniques.A comparison of the three heuristics on a set of test problems shows that simulated annealing and tabu search perform well compared to pure LP-based heuristics, but the effectiveness of the latter heuristics can be improved by combining them with elements from simulated annealing and tabu search.

Multi Item Single Level Capacitated Dynamic Lotsizing Heuristics: A Computational Comparison (Part I: Static Case)

Abstract The multi item single level capacitated dynamic lotsizing problem consists of scheduling N items over a horizon of T periods. Demands are given and should be satisfied without backlogging. The objective is to minimize the sum of setup costs and inventory holding costs over the horizon subject to a constraint on total capacity in each period. Three simple heuristics from literature (Lambrecht and Vanderveken, Dixon and Silver, Dogramaci, Panayiotopoulos and Adam) are compared on a large set of test problems and their difference in performance is analyzed for various problem parameters.

A simple heuristic for the multi item single level capacitated lotsizing problem

This paper presents a fast and flexible heuristic for the multi item capacitated lotsizing problem. The lotsizing step requires only O(NT) computations which is at least an order of magnitude faster than other well-known heuristics. The method is flexible since it allows the user to specify features such as how to sort items, which criterion to use in combining lots and how to search the demand matrix. Extensive computational results show that the new method outperforms existing heuristics both in terms of average solution quality and required computation times.

The effect of individual HR domains on financial performance: evidence from Belgian small businesses

The contribution of this study, which assesses the influence of HRM on financial performance, is fourfold. (1) We assess the relative contribution of different HR domains to organizational performance. By controlling for the overall HRM intensity in all analyses we try to meet one of the most striking shortcomings of ‘single HR practice research’, namely the neglect of the potential simultaneity that might exist with other HR practices. (2) By studying small Belgian companies, we focus on the importance of HRM for small business management. (3) Relying on bankruptcy prediction models, we optimize the conceptualization of financial performance. (4) Using structural equation modelling, we try to capture the mediating effect of operational performance on the relationship between HRM and financial performance. The analyses indicate mixed results for different HR domains with regard to their impact on operational and financial performance.

Set partitioning and column generation heuristics for capacitated dynamic lotsizing

Abstract This paper discusses set partitioning and column generation heuristics for the multi item single level capacitated dynamic lotsizing problem. Most previous research efforts reported in literature use the single item uncapacitated problem solutions as candidate plans. In this paper a different approach is proposed in which candidate plans are also generated by some well-known multi item capacitated dynamic lotsizing heuristics. The LP relaxation of a set partitioning model is solved and rounded to obtain an integer solution. A number of heuristics are subsequently applied to improve upon this initial solution. Heuristics are also used to convert the possibly fractional solution from the column generation step to a feasible integer one. Our methods are compared with other common sense heuristics. Computational experience shows that our methods perform best for problems with fewer periods than items, but are quite good on average.

SMEs' Radical Product Innovation: The Role of Internally and Externally Oriented Knowledge Capabilities

This study examines the role and contribution of specific internally (knowledge diversity and sharing capabilities) and externally oriented knowledge‐related capabilities (exploratory, transformative, and exploitative learning processes of absorptive capacity) to radical product innovation in small and medium‐sized enterprises (SMEs). It extends the current literature on the topic by considering both types of knowledge‐related capabilities and by hypothesizing and testing connections between both. Our path analysis results, based on a sample of 194 SMEs in dynamic environments, indicate that radical innovation is positively affected by exploitative learning and by the knowledge sharing capability. Implications and suggestions for future research are discussed.

A Branch and Bound Algorithm for the Multi Item Single Level Capacitated Dynamic Lotsizing Problem

In this paper we present a branch and bound algorithm for the multi item capacitated lotsizing problem. The bounding procedure is based on a Lagrangean relaxation of the problem. The multipliers are updated using subgradient optimization.

Multi Item Single Level Capacitated Dynamic Lotsizing Heuristics: A Computational Comparison (Part II: Rolling Horizon)

Abstract In this paper we discuss the behavior of three well-known heuristics for capacitated dynamic lotsizing (Lambrecht-Vanderveken, Dixon-Silver, Dogramaci, Panayiotopoulos and Adam) on a rolling horizon. Extensive computational results are presented for various problem parameters. For a detailed discussion of the heuristics and their behavior under static conditions, the reader is referred to Part I of this paper.