• A comparison and hybridization of crossover operators for the nurse scheduling problem

      Maenhout, Broos; Vanhoucke, Mario (Annals of Operations Research, 2007)
    • A heuristic procedure to solve the project staffing problem with discrete time/resource trade-offs and personnel scheduling constraints

      Van Den Eeckhout, Mick; Maenhout, Broos; Vanhoucke, Mario (Computers & Operations Research, 2019)
      Highlights • Project staffing with discrete time/resource trade-offs and calendar constraints. • An iterated local search procedure is proposed. • Different problem decomposition techniques are applied. Abstract When scheduling projects under resource constraints, assumptions are typically made with respect to the resource availability and activities are planned each with its own duration and resource requirements. In resource scheduling, important assumptions are made with respect to the staffing requirements. Both problems are typically solved in a sequential manner leading to a suboptimal outcome. We integrate these two interrelated scheduling problems to determine the optimal personnel budget that minimises the overall cost. Integrating these problems increases the scheduling flexibility, which improves the overall performance. In addition, we consider some resource demand flexibility in this research as an activity can be performed in multiple modes. In this paper, we present an iterated local search procedure for the integrated multi-mode project scheduling and personnel staffing problem. Detailed computational experiments are presented to evaluate different decomposition heuristics and comparison is made with alternative optimisation techniques.
    • A hybrid scatter search heuristic for personalized crew rostering in the airline industry

      Maenhout, Broos; Vanhoucke, Mario (European Journal of Operational Research, 2010)
    • A perturbation matheuristic for the integrated personnel shift and task rescheduling problem

      Maenhout, Broos; Vanhoucke, Mario (European Journal of Operational Research, 2018)
      In this paper, we propose a heuristic optimisation procedure for the integrated personnel shift and task re-scheduling problem. We assume that schedule disruptions arise as the baseline personnel roster is subject to three sources of operational variability, i.e. uncertainty of capacity, uncertainty of demand and uncertainty of arrival. In order to restore the feasibility of the personnel roster and to minimise the number of deviations compared to the original roster, we propose a heuristic re-scheduling procedure that thrives on a perturbation mechanism to diversify the search and a variable neighbourhood search to intensify the search in the region of a solution point. In the computational experiments, we assess the contribution of the different algorithmic building blocks and benchmark our algorithm with other optimisation procedures.
    • A resource type analysis of the integrated project scheduling and personnel staffing problem

      Maenhout, Broos; Vanhoucke, Mario (Annals of Operations Research, 2017)
      In the integrated project scheduling and personnel staffing problem the project activities are scheduled and simultaneously a staffing plan is composed to carry out a single project. In this way, the project schedule that leads to the staffing plan with minimum cost is determined. In this paper, we evaluate different scheduling policies and practices for different personnel resource types. We examine the impact on the staffing cost when the personnel resources are scheduled in a cyclic versus a non-cyclic manner for different (days on, days off)-patterns. Furthermore, the impact of introducing more flexible resource types, such as overtime and temporary help, is explored in relationship with the activity resource demand variability. Computational results show that non-cyclic scheduling leads to a considerable lower staffing cost under all circumstances compared to cyclic scheduling. However, despite the tractability of the resource requirements, flexible temporary resources are essential on top of the regular personnel resources to respond to the variability in demand. The addition of overtime on a strategic staffing level only marginally decreases the personnel cost.
    • A scatter search for the extended resource renting problem

      Vandenheede, Len; Vanhoucke, Mario; Maenhout, Broos (International Journal of Production Research, 2016)
      In this paper, the extended Resource Renting Problem (RRP/extended) is presented. The RRP/extended is a time-constrained project scheduling problem, in which the total project cost is minimised. In the RRP/extended, this total project cost is determined by a number of extra costs, which are defined in this paper. These costs are based on the costs that are used in the traditional Resource Renting Problem and the Total Adjustment Cost Problem. Therefore, the RRP/extended represents a union of these two problems. To solve the RRP/extended, a scatter search is developed. The building blocks of this scatter search are specifically designed for the RRP/extended. We introduce two crossovers and an improvement method. The efficiency of these building blocks will be shown in the paper. Furthermore, a sensitivity analysis is presented in which the five costs have diverse values.
    • An artificial immune system based approach for solving the nurse re-rostering problem.

      Maenhout, Broos; Vanhoucke, Mario (Lecture notes in Computer Science, 2013)
      Personnel resources can introduce uncertainty in the operational processes. Constructed personnel rosters can be disrupted and render infeasible rosters. Feasibility has to be restored by adapting the original announced personnel rosters. In this paper, an Artificial Immune System for the nurse re-rostering problem is presented. The proposed algorithm uses problem-specific and even roster-specific mechanisms which are inspired on the vertebrate immune system. We observe the performance of the different algorithmic components and compare the proposed procedure with the existing literature.
    • An electromagnetic Meta-heuristic for the Nurse Scheduling Problem

      Maenhout, Broos; Vanhoucke, Mario (Journal of Heuristics, 2007)
    • An electromagnetism meta-heuristic for the nurse scheduling problem

      Maenhout, Broos; Vanhoucke, Mario (2005)
      In this paper, we present a novel meta-heuristic technique for the nurse scheduling problem (NSP). This well-known scheduling problem assigns nurses to shifts per day taking both hard and soft constraints into account. The objective is to maximize the preferences of the nurses and to minimize the total penalty cost from violations of the soft constraints. The problem is known to be NP-hard. Due to its complexity and relevance, many algorithms have been developed to solve practical, and often case-specific versions of the NSP. The enormous amount of different constraints has led to an overwhelming amount of exact and meta-heuristic procedures, and hence comparison and state-of-the-art reporting of standard results seem to be a utopian idea. The contribution of this paper is twofold. First, we present a meta-heuristic procedure for the NSP based on the framework proposed by Birbil and Fang (2003). The Electromagnetic (EM) approach is based on the theory of physics, and simulates attraction and repulsion of sample points in order to move towards a promising solution. Second, we present computational experiments on a standard benchmark dataset, and solve problem instances under different assumptions. We show that our procedure performs consistently well under many different circumstances, and hence, can be considered as robust against case-specific constraints. Keywords: meta-heuristics, electromagnetism, nurse scheduling
    • An evaluation of the adequacy of project network generators with systematically sampled networks

      Vanhoucke, Mario; Coelho, José; Debels, Dieter; Maenhout, Broos; Tavares, Luis (European Journal of Operational Research, 2008)
    • An evolutionary approach for the nurse rerostering problem

      Maenhout, Broos; Vanhoucke, Mario (Computers and Operations Research, 2011)
    • An exact algorithm for an integrated project staffing problem with a homogeneous workforce

      Maenhout, Broos; Vanhoucke, Mario (Journal of Scheduling, 2016)
      When scheduling projects under resource constraints, assumptions are typically made with respect to the resource availability. In resource scheduling problems important assumptions are made with respect to the resource requirements. As projects are typically labour intensive, the underlying (personnel) resource scheduling problems tend to be complex due to different rules and regulations. In this paper, we aim to integrate these two interrelated scheduling problems to minimise the overall cost. For that purpose, we propose an exact algorithm for the project staffing with resource scheduling constraints. Detailed computational experiments are presented to evaluate different branching rules and pruning strategies and to compare the proposed procedure with other optimisation techniques.
    • An integrated nurse staffing and scheduling analysis for longer-term nursing staff allocation problems

      Maenhout, Broos; Vanhoucke, Mario (Omega - International Journal of Management Science, 2013)
      The efficient and effective management of nursing personnel is of critical importance in a hospital's environment comprising a vast share of the operational costs. The adopted nurse workforce practices and policies highly affect the nurses' working conditions and the provided quality of care. Policy decisions on the staffing level have an impact on the outcome of the scheduling level and vice versa. Isolated reasoning typically leads to suboptimal decisions often resulting in ineffective outcomes of care. In order to overcome these inefficiencies, we propose in this paper a new integrative nurse staffing and shift scheduling approach. We test and assess the benefits of our approach in a reallife environment. Moreover, we examine the impact of several personnel policies on the staffing decision.
    • Analyzing the nursing organizational structure and process from a scheduling perspective

      Maenhout, Broos; Vanhoucke, Mario (Health Care Management Science, 2013)
      The efficient and effective management of nursing personnel is of critical importance in a hospital’s environment comprising approximately 25 % of the hospital’s operational costs. The nurse organizational structure and the organizational processes highly affect the nurses’ working conditions and the provided quality of care. In this paper, we investigate the impact of different nurse organization structures and different organizational processes for a real-life situation in a Belgian university hospital. In order to make accurate nurse staffing decisions, the employed solution methodology incorporates shift scheduling characteristics in order to overcome the deficiencies of the many phase-specific methodologies that are proposed in the academic literature.
    • Characterisation and generation of nurse scheduling problem instances

      Vanhoucke, Mario; Maenhout, Broos (2005)
      In this paper, we propose different complexity indicators for the well-known nurse scheduling problem (NSP). The NSP assigns nurses to shifts per day taking both hard and soft constraints into account. The objective is to maximize the nurses' preferences and to minimize the total penalty cost from violations of the soft constraints. The problem is known to be NP-hard. Due to its complexity and relevance in practice, the operations research literature has been overwhelmed by different procedures to solve the problem. The complexity has resulted in the development of several (meta-)heuristic procedures, able to solve a NSP instance heuristically in an acceptable time limit. The practical relevance has resulted in a never-ending amount of different NSP versions, taking practical, case-specific constraints into account. The contribution of this paper is threefold. First, we describe our complexity indicators to characterize a nurse scheduling problem instance. Secondly, we develop a NSP generator to generate benchmark instances to facilitate the evaluation of existing and future research techniques. Finally, we perform some preliminary tests on a simple IP model to illustrate that the proposed indicators can be used as predictors of problem complexity. Keywords: Nurse scheduling, Benchmark instances, Problem classification
    • Comparison and hybridization of crossover operators for the nurse scheduling problem

      Maenhout, Broos; Vanhoucke, Mario (Annals of Operations Research, 2008)