General Introduction

The mission of the Stochastic Operations Research group (SOR) is to conduct mathematical education and research of internationally high standards in the areas of stochastic processes and mathematics of operations research, to contribute to the development of mathematics in a multidisciplinary engineering environment, and contribute to a better understanding and functioning of our increasingly complex society.

Operations Research aims at the development of mathematical models and methods for the design, control and optimisation of complex systems. Within this broad field, SOR focuses on mathematical challenges in the area of stochastic processes, and its engineering environment in societally relevant areas. Operations Research techniques focus on improving efficiency, but at the same time improved efficiency often leads to increased job satisfaction: experienced work load is dominated by those moments at which the work pressure is very high. Improved efficiency may also improve safety since errors due to peak workload may be avoided.

The fundamental mathematical areas of expertise of SOR include probability theory, with emphasis on stochastic processes, and random graphs. The bridge to engineering applications is established through areas of expertise that include the theory of games, stochastic dynamic programming, queues, polling systems, large deviations and discrete event simulation. Typical application areas are in communications (wireless ad-hoc networks, sensor networks, energy minimization in networks), social and professional networks (virus spread, collaboration, citation structure, ranking of web pages), transportation, production & logistics (facility location, supply chains, production systems, inventory management, road traffic), and health care (patient logistics, treatment and diagnostics planning, medication).

Communications systems

Internet and World Wide Web are closely intertwined with the telecommunications infrastructure. Connections in these systems may be wired or wireless, may have high or low bandwidth and may be reliable or unreliable. The connection infrastructure is of utmost importance for our experienced performance in such networks. Typical problems include the design of reliable networks and of energy efficient routing and coding algorithms, while guaranteeing delay constraints. The results have applications in `smart dust’ sensor networks, ad-hoc networks for emergency services and the internet of things. The smart dust networks consist of huge amounts of autonomous tiny sensors with limited communication capabilities that are deployed to monitor remote areas. The emergency services use ad-hoc networks to improve their awareness of the situation by sharing images, and videos, when they an area struck by a catastrophe in which no infrastructure is present. The internet of things will be a crucial aspect in many future applications, including smart industry. Performance modeling and analysis of these networks is based on properties of the underlying random graph structure combined with queueing models for investigating, for instance, energy harvesting capabilities and network delays. Information theory provides an insight in the key characteristics of optimal protocols.

Social networks and Big Data

cid:E93010C9-A058-456D-A3D8-F46C893F65C5We are currently witnessing a data revolution. Massive amounts of data can be streamed in real time from industrial processes, online social interactions, financial transactions, and Internet of things. While big data is easily available, its analysis and interpretation remains largely an open problem. This in particular is true for network data, for example: can we make our society more efficient by acting upon social interactions on Twitter and Facebook? Can we predict development of science and innovation using citation networks? Can we predict and prevent epidemics in computers and humans? Can we predict stability of a company through its financial interactions? Attacking these problems requires development of new network algorithms as well as mathematical tools for their analysis, based on the theory of random graphs, stochastic processes, and statistics.

Health care logistics

Health care expenditures in the Netherlands may increase from roughly 10% of GDP in 2010 to roughly 20% in 2035. This increase is to a large extent due to our ageing population in which the percentage of people over 65 will increase from roughly 15% to roughly 25% in the same period. Sustaining the current quality of care seems to require a rapidly increasing percentage of the work force to be employed in the health care sector, while there already is a shortage in health care staff. Typical challenges include efficient planning of operating theatres, balancing the number of patients in wards to reduce peaks and therefore increase the efficiency of nursing care, efficient rostering of staff to allow for more work to be done by the same number of people. Addressing these challenges requires a broad spectrum of techniques from Operations Research, including queueing theory, dynamic programming, game theory, discrete event simulation, discrete optimisation, mathematical programming and scheduling.

Research in healthcare is concentrated in the Center for Healthcare Operations Improvement and Research (CHOIR), see our brochure or Implementation of the results is, in part, carried out via our spin-off Rhythm bv., see

Transportation, production & logistics

In our modern society, transport, production, logistics and communications are closely related. Households use the Internet for shopping, which changes the entire supply chain from localized to distributed chains, and affects mobility patterns since the ordered goods are transported from the suppliers to the households. Road status information sent via the communications system will allow active steering of road traffic to e.g. minimize delay or pollution. In large transportation systems, such as container or flower distribution, next generation RFIDs (wireless sensor networks) build up a distributed communication system to route containers with minimal delay. Seemingly independent elements of societal and business life will become more and more interrelated. The modern urbanized society will become a single self-organizing system. Typical problems include development of cooperative distribution schemes for cities such that e.g. only a single truck will deliver goods in one street, and design of routing schemes for both messages and goods to minimize transportation delay (Internet of Things). Such problems may be addressed via a combination of game theory and queueing theory to integrated fair cost allocation into delay sensitive systems.

Application and implementation approach

Employing Operations Research techniques seems to be dedicated to improving efficiency, at the same time improved efficiency leads to increased job satisfaction as experienced work load is often dominated by those moments at which the work pressure is very high, and it also improves patient safety since errors due to peak work load will be avoided. Health care is in dire straits. Fortunately, more and more health care organizations are realizing that Operations Research may provide an approach to sustain our health care system. Such an approach requires close collaboration between Operations Research specialists and health care professionals to tackle resource optimization challenges of the health care sector and implement their solutions in health care organisations.

Application area


Communications systems

Maurits de Graaf (

Social and professional networks

Nelly Litvak (

Transportation, production & logistics

Jan-Kees van Ommeren (

Health care logistics

Richard Boucherie (