Dr Wolfgang Garn


Senior Lecturer in Analytics
PhD, MSc, BSc (Hons)
+44 (0)1483 682005
Please email me

Biography

Affiliations and memberships

AIS
Association for Information Systems
ARGESIM
Working Group Simulation News
EURO
The Association of European Operational Research Societies
EUROSIM
Federation of European Simulation Societies
FITCE
Federation of Telecommunications Engineers of the European Community
INFORMS
Institute for Operations Research and the Management Sciences
ÖGOR
Austrian Society of Operations Research

Research

Research interests

Research projects

Indicators of esteem

  • Reviewer for the ...

    • European Journal of Operational Research
    • Neurocomputing Journal
    • International Journal of Production Economics
    • International Conference on Information Systems
    • and many more

My teaching

Supervision

Postgraduate research supervision

My publications

Publications

In this paper a demand time series is analysed to support Make-To-Stock (MTS) and Make-To-Order (MTO) production decisions. Using a purely MTS production strategy based on the given demand can lead to unnecessarily high inventory levels thus it is necessary to identify likely MTO episodes. This research proposes a novel outlier detection algorithm based on special density measures. We divide the time series' histogram into three clusters. One with frequent-low volume covers MTS items whilst a second accounts for high volumes which is dedicated to MTO items. The third cluster resides between the previous two with its elements being assigned to either the MTO or MTS class. The algorithm can be applied to a variety of time series such as stationary and non-stationary ones. We use empirical data from manufacturing to study the extent of inventory savings. The percentage of MTO items is reflected in the inventory savings which were shown to be an average of 18.1%.
Louvieris P, Garn W (2013) Novel conditional probability generation methods for high reliability effects-based decision making, Decision Support Systems
Garn W, Aitken J (2013) Production scheduling in the food industry,
In this paper we study the optimality of production schedules in the food industry. Specifically we are interested whether stochastic economic lot scheduling based on aggregated forecasts outperforms other lot sizing approaches. Empirical data on the operation?s customer side such as product variety, demand and inventory is used. Hybrid demand profiles are split into make-to-order (MTO) and make-to-stock (MTS) time series. We find that the MTS demand aggregation stabilizes, minimizes change-overs, and optimizes manufacturing.
Garn W (2010) Issues in Operations Management, Pearson
This book explores a set of critical areas of Operations Management in depth.
The contents covers topics such as:
- Waiting Line Models (e.g. Multiple Server Waiting Line)
- Transportation and Network Models (e.g. Shortest Route)
- Inventory Management (e.g. Economic Order Quantity model)

This will enable the reader:
- To increase the efficiency and productivity of business firms
- To observe and define ?challenges? in a concise, precise and logical manner
- To be familiar with a selected number of classical and state-of-the art Management Science methods and tools to solve management problems
- To create solution models, to develop and create procedures that offer competitive advantage to the business/organisation
- To communicate and provide results to the management for decision making and implementation

Garn W, Louvieris P (2015) Conditional probability generation methods for high reliability effects-based decision making, arXiv (Computer Science > Artificial Intelligence) arXiv:1512.08553 [cs.AI]
Decision making is often based on Bayesian networks. The building blocks for Bayesian networks are its conditional probability tables (CPTs). These tables are obtained by parameter estimation methods, or they are elicited from subject matter experts (SME). Some of these knowledge representations are insufficient approximations. Using knowledge fusion of cause and effect observations lead to better predictive decisions. We propose three new methods to generate CPTs, which even work when only soft evidence is provided. The first two are novel ways of mapping conditional expectations to the probability space. The third is a column extraction method, which obtains CPTs from nonlinear functions such as the multinomial logistic regression. Case studies on military effects and burnt forest desertification have demonstrated that so derived CPTs have highly reliable predictive power, including superiority over the CPTs obtained from SMEs. In this context, new quality measures for determining the goodness of a CPT and for comparing CPTs with each other have been introduced. The predictive power and enhanced reliability of decision making based on the novel CPT generation methods presented in this paper have been confirmed and validated within the context of the case studies.
Garn W (2003) A Real-World S-MD-mVRP-TW,
Aitken J, Garn W (2012) Process variance: Competing Against Customer Demand,
Aitken J, Garn W (2014) Stochastic operations optimisation for delivery services,
The purpose of this paper is to investigate the use of business analytics as a method for developing understanding of the environment that delivery service organisations operate within and how this comprehension can support the evolution and implementation of lean thinking. Mapping complex and dynamic environments in a manner which provides sufficient insight, clarity and organisational learning is a challenge when utilising traditional lean value stream mapping tools.
Through modelling and experimentation organisations and individuals can reshape their cognitive maps to develop and recognise new opportunities to improve their processes through improving the presentation and use of information.
Van Der Heijden H, Garn W (2013) Profitability in the car industry: New measures for estimating targets and target directions, European Journal of Operational Research 225 (3) pp. 420-428 Elsevier
In this paper we study the profitability of car manufacturers in relation to industry-wide profitability targets such as industry averages. Specifically we are interested in whether firms adjust their profitability in the direction of these targets, whether it is possible to detect any such change, and, if so, what the precise nature is of these changes. This paper introduces several novel methods to assess the trajectory of profitability over time. In doing so we make two contributions to the current body of knowledge regarding the dynamics of profitability. First, we develop a method to identify multiple profitability targets. We define these targets in addition to the commonly used industry average target. Second, we develop new methods to express movements in the profitability space from t to t + j, and define a notion of agreement between one movement and another. We use empirical data from the car industry to study the extent to which actual movements are in alignment with these targets. Here we calculate the three targets that we have previously identified, and contrast them with the actual profitability movements using our new agreement measure. We find that firms tend to move more towards to the new targets we have identified than to the common industry average. © 2012 Elsevier B.V. All rights reserved.
Garn W (2009) Chess with "Greedy Edi", Matlab-Central
You can play against "Edi" a chess program using Matlab. It uses a greedy heuristic to find the "best" move.
Garn W (2010) Predictive Power Decisions with Generated Conditional Probabilities,
Lean and Swift-Even-Flow (SEF) operations are compared in the context of sorting facilities. Lean approaches tend to attack parts of their processes for improvement and waste reduction, sometimes overlooking the impact this will have on their overall pipeline. A SEF approach on the other hand is driven by a desire to reduce variations by enabling the practitioner to visualise himself as the material that flows through the system thus unearthing all the problems that occur in the process as a whole. This study integrates Discrete Event Simulations (DES) into the lean and SEF framework. A real world case study with high levels of variations is used to gain insights and to derive relevant simulation models. The models were used to find the optimal configuration of machines and labour such that the operational costs are minimised. It was found that DES and SEF have a common basis. Lean processes as well as SEF processes both converge to similar solutions. However, SEF arrives faster at a near optimum solution. DES is a valuable tool to model, support and implement the lean and SEF approach. The SEF approach is superior to lean processes in the initial phases of a business process optimisation. The primary novelty of this study is the usage of DES to compare the lean and SEF approach. This study presents a systematic approach of how DES and optimisation can be applied to lean and SEF operations.
Garn WOLFGANG (2015) Drones reveal efficiency savings in delivery services,
Drone delivery services (DDS) are an upcoming reality. Companies such as Amazon, DHL and Google are investing in developments in this area. German?s parcel delivery company DHL has begun applying them commercially. This emphasises the importance to have insights in the economic benefits of drone delivery services. This study compares drone delivery services with traditional delivery services. It looks at the cost effectiveness of integrating drones into a delivery services? operations. The study identifies and categorise factors that control the delivery operations. It develops a mathematical model that compares 3D flight paths of a fleet of drones with a fleet of 2D van routes. The developed method can be seen as an extension of the Vehicle Routing Problem (VRP). Efficiency savings of drone services of real world rural postcode sectors are analysed. The study limits itself to the use of small unmanned aerial vehicles (UAVs) with a low payload, which are GPS controlled and autonomous. The case study shows time, distance and cost savings when using drones rather than delivery vans. The model reveals efficiency factors to operate DDS. The study shows the economic necessity for delivering low weight goods via DDS. The primary methodological novelty of this study is a model that integrates factors relevant to drones into the VRP.
Louvieris P, Gregoriades A, Garn W (2010) Assessing critical success factors for military decision support, EXPERT SYSTEMS WITH APPLICATIONS 37 (12) pp. 8229-8241 PERGAMON-ELSEVIER SCIENCE LTD
Aitken J, Bozarth C, Garn W (2016) To eliminate or absorb supply chain complexity: A conceptual model and case study, Supply Chain Management 21 (6) pp. 759-774 Emerald Group Publishing Limited
Existing works in the supply chain complexity area have either focused on the overall behavior of multi-firm complex adaptive systems (CAS) or on listing specific tools and techniques that business units (BUs) can use to manage supply chain complexity, but without providing a thorough discussion about when and why they should be deployed. This research seeks to address this gap by developing a conceptually sound model, based on the literature, regarding how an individual BU should reduce versus absorb supply chain complexity. This research synthesizes the supply chain complexity and organizational design literature to present a conceptual model of how a BU should respond to supply chain complexity. We illustrate the model through a longitudinal case study analysis of a packaged foods manufacturer. Regardless of its type or origin, supply chain complexity can arise due to the strategic business requirements of the BU (strategic) or due to suboptimal business practices (dysfunctional complexity). Consistent with the proposed conceptual model, the illustrative case study showed that a firm must first distinguish between strategic and dysfunctional drivers prior to choosing an organizational response. Furthermore, it was found that efforts to address supply chain complexity can reveal other system weaknesses that lie dormant until the system is stressed. The case study provides empirical support for the literature-derived conceptual model. Nevertheless, any findings derived from a single, in-depth case study require further research to produce generalizable results. The conceptual model presented here provides a more granular view of supply chain complexity, and how an individual BU should respond, than what can be found in the existing literature. The model recognizes that an individual BU can simultaneously face both strategic and dysfunctional complexity drivers, each requiring a different organizational response. We are aware of no other research works that have synthesized the supply chain complexity and organizational design literature to present a conceptual model of how an individual business unit (BU) should respond to supply chain complexity. As such, this paper furthers our understanding of supply chain complexity effects and provides a basis for future research, as well as guidance for BUs facing complexity challenges.
Garn W, Aitken J (2015) Agile factorial production for a single manufacturing line with multiple products, European Journal of Operational Research 245 (3) pp. 754-766 Elsevier
Industrial practices and experiences highlight that demand is dynamic and non-stationary. Research however has historically taken the perspective that stochastic demand is stationary therefore limiting its impact for practitioners. Manufacturers require schedules for multiple products that decide the quantity to be produced over a required time span. This work investigated the challenges for production in the framework of a single manufacturing line with multiple products and varying demand. The nature of varying demand of numerous products lends itself naturally to an agile manufacturing approach. We propose a new algorithm that iteratively refines production windows and adds products. This algorithm controls parallel genetic algorithms (pGA) that find production schedules whilst minimizing costs. The configuration of such a pGA was essential in influencing the quality of results. In particular providing initial solutions was an important factor. Two novel methods are proposed that generate initial solutions by transforming a production schedule into one with refined production windows. The first method is called factorial generation and the second one fractional generation method. A case study compares the two methods and shows that the factorial method outperforms the fractional one in terms of costs.
Garn Wolfgang, Hu Yin, Nicholson Paul, Jones Bevan, Tang Hongying (2018) LSTM network time series predicts high-risk tenants, Proceedings of Euro 2018 - 29th European Conference on Operational Research EURO 2018
In the United Kingdom, local councils and housing associations provide social housing at secure, low-rent housing options to those most in need. Occasionally tenants have difficulties in paying their rent on time and fall into arrears. The lost revenue can cause financial burden and stress to tenants. An efficient arrear management scheme is to target those who are more at risk of falling into long-term arrears so that interventions can avoid lost revenue. In our research, a Long Short-Term Memory Network (LSTM) based time series prediction model is implemented to differentiate the high-risk tenants from temporary ones. The model measures the arrear risk for each individual tenant and differentiates between short-term and long-term arrears risk. Furthermore it predicts the trajectory of arrears for each individual tenant. The arrears analysis investigates factors that provide assistance to tenants to trigger preventions before their debt becomes unmanageable. A five-years rent arrears dataset is used to train and evaluate the proposed model. The root mean squared error (RMSE) punishes large errors by measuring differences between actually observed and predicted arrears. The novel model benefits the sector by allowing a decrease in lost revenue; an increase in efficiency; and protects tenants from unmanageable debt.
Kireulishvili George, Garn Wolfgang, Aitken James, Hemsley-Brown Jane (2018) Prediction methods improve bus services profitability, Proceedings of Euro 2018 - 29th European Conference on Operational Research EURO 2018
Since the bus deregulation (Transport Act 1985) the patronage for bus
services has been decreasing in a county in South of England. Hence,
methods that increase patronage, focus subsidies and stimulate the bus
industry are required. Our surveys and market research identified and
quantified essential factors. The top three factors are price, frequency,
and dependability. The model was further enhanced by taking into
account real time passenger information (RTPI), socio-demographics
and ticket machine data along targeted bus routes. These allowed the
design of predictive models. Here, feature engineering was essential
to boost the solution quality. We compared several models such as
regression, decision tress and random forest. Additionally, traditional
price elasticity formulas have been confirmed. Our results indicate
that more accuracy can be gained using prediction methods based on
the engineered features. This allows to identify routes that have the
potential to increase in profitability - allowing a more focused subsidy
strategy.