WorldCat Identities

Creemers, Stefan

Overview
Works: 21 works in 23 publications in 2 languages and 26 library holdings
Roles: Author, Other
Publication Timeline
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Most widely held works by Stefan Creemers
Bedrijfswagens in het recht by Lode Agache( Book )

1 edition published in 2012 in Dutch and held by 3 WorldCat member libraries worldwide

Minimizing the expected makespan of a project with stochastic activity durations under resource constraints by Stefan Creemers( )

2 editions published in 2015 in English and held by 2 WorldCat member libraries worldwide

The resource-constrained project scheduling problem (RCPSP) has been widely studied. A fundamental assumption of the basic type of RCPSP is that activity durations are deterministic (i.e., they are known in advance). In reality, however, this is almost never the case.In this article we illustrate why it is important to incorporate activity duration uncertainty, and develop an exact procedure to optimally solve the stochastic resource-constrained scheduling problem (SRCPSP). A computational experiment shows that our approach works best when solving small-to medium-sized problem instances where activity durations have a moderate-to-high level of variability. For this setting, our model outperforms the existing state-of-the-art.In addition, we use our model to assess the optimality gap of existing heuristic approaches, and investigate the impact of making scheduling decisions also during the execution of an activity rather than only at the end of an activity
New strategies for stochastic resource-constrained project scheduling by Salim Rostami( )

1 edition published in 2017 in English and held by 2 WorldCat member libraries worldwide

Project Planning with Alternative Technologies in Uncertain Environments by Stefan Creemers( )

2 editions published between 2013 and 2014 in English and held by 2 WorldCat member libraries worldwide

We investigate project scheduling with stochastic activity durations to maximize the expected net present value. Individual activities also carry a risk of failure, which can cause the overall project to fail. To mitigate the risk that an activity's failure jeopardizes the entire project, more than one alternative may exist for reaching the project's objectives, and these alternatives can be implemented either in parallel or in sequence. In the project planning literature, such technological uncertainty is typically ignored and project plans are developed only for scenarios in which the project succeeds. We propose a model that incorporates both the risk of activity failure and the possible pursuit of alternative technologies. We find optimal solutions to the scheduling problem by means of stochastic dynamic programming. Our algorithms prescribe which alternatives need to be explored, and whether they should be investigated in parallel or in sequence. We also examine the impact of the variability of the activity durations on the project's value
New Benchmark Results for the Stochastic Resource-Constrained Project Scheduling Problem by Salim Rostami( )

1 edition published in 2016 in English and held by 1 WorldCat member library worldwide

We study the stochastic resource-constrained project scheduling problem or SRCPSP, where project activities have stochastic durations. A solution is a scheduling policy, and we propose a new class of policies that is a generalization of most of the classes described in the literature. A policy in this new class makes a number of a-priori decisions in a preprocessing phase while the remaining scheduling decisions are made online. A two-phase local search algorithm is proposed to optimize within the class. Our computational results show that the algorithm has been efficiently tuned towards finding high-quality solutions, and that it outperforms all existing algorithms for large instances. The results also indicate that the optimality gap even within the larger class of elementary policies is very small
The Preemptive Stochastic Resource-Constrained Project Scheduling Problem An Efficient Globally Optimal Solution Procedure by Stefan Creemers( )

1 edition published in 2016 in English and held by 1 WorldCat member library worldwide

We present a globally optimal solution procedure to tackle the preemptive stochastic resource-constrained project scheduling problem (PSRCPSP). A solution to the PSRCPSP is a policy that allows to construct a precedence- and resource-feasible schedule that minimizes the expected makespan of a project. The PSRCPSP is an extension of the stochastic resource-constrained project scheduling problem (SRCPSP) that allows activities to be interrupted. The SRCPSP and PSRCPSP both assume that activities have stochastic durations. Even though the deterministic preemptive resource-constrained project scheduling problem (PRCPSP) has received some attention in the literature, we are the first to study the PSRCPSP. We use phase-type distributions to model the stochastic activity durations, and define a new Continuous-Time Markov Chain (CTMC) that drastically reduces memory requirements when compared to the well-known CTMC of Kulkarni and Adlakha (1986). In addition, we also propose a new and efficient approach to structure the state space of the CTMC. These improvements allow us to easily outperform the current state-of-the-art in optimal project scheduling procedures, and to solve instances of the PSPLIB J90 and J120 data sets. Last but not least, if activity durations are exponentially distributed, we show that elementary policies are globally optimal for the SRCPSP and the PSRCPSP
Dynamic order acceptance and capacity planning in a stochastic multi-project environment with a bottleneck resource( )

1 edition published in 2018 in English and held by 1 WorldCat member library worldwide

Abstract : We study the integration of order acceptance and capacity planning in multi-project environments with dynamically arriving projects. We model this planning problem as a continuous-time Markov decision process to determine long-term optimal decisions. We examine whether macro-process planning should be performed before or after order acceptance. We characterise the structure of optimal policies, and explore the dependence on a number of parameters such as project payoff, project cost and order arrival time. We also look into the effects of set-up costs and the use of non-regular capacity
Healthcare queueing models by Stefan Creemers( )

1 edition published in 2008 in English and held by 1 WorldCat member library worldwide

The optimal allocation of server time slots over different classes of patients by Stefan Creemers( )

1 edition published in 2011 in English and held by 1 WorldCat member library worldwide

A new approach for quantitative risk analysis by Stefan Creemers( )

1 edition published in 2010 in English and held by 1 WorldCat member library worldwide

Two Sequencing Problems Equivalence, Optimal Solution, and State-of-the-Art Results by Stefan Creemers( )

1 edition published in 2017 in English and held by 1 WorldCat member library worldwide

We show that the serial SNPV and the LCFDP are equivalent. The serial SNPV is a special case of the SNPV that tries maximize the expected NPV of a project by sequencing activities that have stochastic durations and cash flows that are incurred at the start of an activity. The LCFDP, on the other hand, minimizes the expected cost of the sequential diagnosis of a set of tests that have known execution costs and failure probabilities
Modeling a healthcare system as a queueing network : the case of a Belgian hospital( )

1 edition published in 2007 in English and held by 1 WorldCat member library worldwide

Precedence Theorems and Dynamic Programming for the Single-Machine Weighted Tardiness Problem by Salim Rostami( )

1 edition published in 2017 in English and held by 1 WorldCat member library worldwide

Schrage and Baker (1978) proposed a generic dynamic programming (DP) algorithm to tackle precedenceconstrained sequencing on a single machine. The performance of their DP method, however, is limited due to excessive memory requirements, particularly when the precedence network is not very dense. Emmons (1969) and Rinnooy Kan et al. (1975) described a set of precedence theorems for sequencing jobs on a single machine in order to minimize total weighted tardiness, which were later generalized by Kanet (2007). These theorems distinguish dominant precedence constraints for a job pool that is initially without precedence relation. In this paper, we connect and extend the findings of the aforementioned articles. We develop a framework for applying Kanet's theorems to the precedence-constrained problem, and we propose an exact DP algorithm that utilizes a new efficient memory management technique. Our procedure outperforms the state-of-the-art algorithm for instances with medium to high network density. Furthermore, we empirically verify the computational gain of using Kanet's rather than Emmons' theorems
Extending the production dice game( )

1 edition published in 2010 in English and held by 1 WorldCat member library worldwide

A Markov model for measuring service levels in nonstationary G(t)/G(t)/s(t)+G(t) queues by Stefan Creemers( )

1 edition published in 2013 in English and held by 1 WorldCat member library worldwide

Scheduling Markovian PERT networks with maximum-NPV objective by Stefan Creemers( )

1 edition published in 2008 in English and held by 1 WorldCat member library worldwide

Queueing models for appointment-driven systems by Stefan Creemers( )

1 edition published in 2008 in English and held by 1 WorldCat member library worldwide

A Markov Model for Measuring Service Levels in Nonstationary G(t)/G(t)/s(t)+G(t) Queues by Stefan Creemers( )

1 edition published in 2013 in English and held by 1 WorldCat member library worldwide

We present a Markov model to approximate the queueing behavior at the G(t)/G(t)/s(t)+G(t) queue with exhaustive discipline and abandonments. The performance measures of interest are: (1) the average number of customers in queue, (2) the variance of the number of customers in queue, (3) the average number of abandonments and (4) the virtual waiting time distribution of a customer when arriving at an arbitrary moment in time. We use acyclic phase-type distributions to approximate the general interarrival, service and abandonment time distributions. An effi cient, iterative algorithm allows the accurate analysis of small- to medium-sized problem instances. The validity and accuracy of the model are assessed using a simulation study
Sequential testing of n-outof-n systems precedence theorems and exact methods by Salim Rostami( )

1 edition published in 2018 in English and held by 1 WorldCat member library worldwide

Modeling a Healthcare System as a Queueing Network The Case of a Belgian Hospital by Stefan Creemers( )

1 edition published in 2008 in Undetermined and held by 1 WorldCat member library worldwide

The performance of health care systems in terms of patient flow times and utilization of critical resources can be assessed through queueing and simulation models. We model the orthopaedic department of the Middelheim hospital (Antwerpen, Belgium) focusing on the impact of outages (preemptive and nonpreemptive outages) on the effective utilization of resources and on the flowtime of patients. Several queueing network solution procedures are developed such as the decomposition and Brownian motion approaches. Simulation is used as a validation tool. We present new approaches to model outages. The model offers a valuable tool to study the trade-off between the capacity structure, sources of variability and patient flow times
 
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Languages
English (20)

Dutch (1)