Staff profile

Personal webpages

I am a Professor in the Department of Computer Science. I read mathematics at Christ Church, Oxford (1980-83) before completing my PhD in mathematics at Queen Mary College, University of London (1983-86). I was then appointed to a Lecturership in the Computing Laboratory, University of Newcastle upon Tyne in 1986 before moving to a Lecturership in the Department of Computer Science, University of Wales Swansea in 1992. I was later appointed Senior Lecturer (1994) and then Reader (1995) before becoming Professor of Computer Science at Leicester in 1996. I moved to the Department of Computer Science at Durham as Professor in 2002.

Whilst at Leicester, I was Head of the School of Mathematics and Computer Science from 1999-2002 and at Durham I have twice been Head of Computer Science: from 2003-2006 and for 6 months in 2008. I was Director of Research for the School of Engineering and Computing Sciences from 2011-2014 (there was a joint school 2009-2017) but as of 2017 the School of Engineering and Computing Sciences is no more with the Department of Computer Science reconstituted. I was Director of Research for the new department from 2019-2021.

I was a Computer Science and Informatics Panel Member of HEFCE’s Research Excellence Framework (REF) in REF 2014 and again in REF 2021. REF is the system for assessing the quality of research in UK higher education institutions and replaced the Research Assessment Exercise (RAE).

I have been a Member of UK Computing Science Research Committee (UKCRC) since 2002 and was a Member of the Executive Committee 2004-2007. As of October 2013, I rejoined the Executive Committee before standing down at the end of my term in 2016. UKCRC is an expert panel of the Institution of Engineering and Technology (IET) and the British Computing Society (BCS), and aims to promote the vitality, quality and impact of Computing Research in the UK.

I have served the London Mathematical Society (LMS) for some years having been: a Member of LMS Computer Science Committee 1996-99 and Chair 1999-2002; a Member of LMS Publications Committee 1997-99; and a Member of LMS Council 1997-1999. I was also Coordinator of the joint LMS/EPSRC Mathematics for IT (MathFIT) initiative 2000-2002. As of November 2013, I resumed LMS service and was elected to LMS Council. I also joined the Computer Science Committee in February 2014. In January 2015 I became Programme Secretary, chairing (the now defunct) Programme Committee. I stepped down from Council and from being Programme Secretary in November 2018 and from chairing the Society Lectures and Meetings Committee (SLAM) in November 2019. The LMS was founded in 1865 and is the major UK learned society for Mathematics.

The BCS Academy of Computing is a learned society dedicated to advancing computing as an academic discipline. The Academy mission is to advance the creation, study and application of knowledge in computing for the benefit of society. I was a Member of BCS Academy Board, which is the most senior committee within the Academy, before resigning in 2016. I am also a Fellow of the BCS.

In deciding how best to meet the needs of peer review of research proposals, the EPSRC established a college of experts, nominated by those active in the research field concerned, to provide a broadly based community from which to obtain peer review advice. I am a member of the EPRSC Peer Review College and have been since its inauguration.

The Computer Journal was established in 1958 and is published by Oxford University Press on behalf of the BCS. It is split into four sections and publishes research papers in a full range of subject areas, as well as regular feature articles and occasional themed issues. The journal provides a complete overview of developments in the field of Computer Science. I have been an Associate Editor for some years but in January 2014 I became Section Editor of Section A: Computer Science Theory, Methods and Tools. I stood down at the end of 2021.

The Philosophical Transactions of the Royal Society A was founded in 1660 and is the world’s first scientific journal. It publishes high quality theme issues on topics of current importance and general interest within the physical, mathematical, and engineering sciences. As of January 2017, I joined its Editorial Board.

I was a member of the Advisory Board of the Springer book series Undergraduate Topics in Computer Science (UTICS) for many years before standing down at the end of 2021.

I have previously been: President of the British Colloquium for Theoretical Computer Science (BCTCS); President of the European Association for Computer Science Logic (EACSL); an editorial board member of the (now defunct) Journal of Discrete Algorithms (as published by Elsevier); and an editor of the (now defunct) LMS Journal of Computation and Mathematics (as published by CUP).

• computational complexity
• finite model theory and descriptive complexity
• graph theory and algorithms
• group theory
• interconnection networks for parallel and distributed computing
• theoretical aspects of artificial intelligence

Chapter in book

• Stewart, I. (1999). A perspective on Lindström quantifiers and oracles. In J. Väänänen (Ed.), Generalized quantifiers and computation : 9th European Summer School in Logic, Language, and Information ESSLLI’97 Workshop, 11-22 August 1997, Aix-en-Provence, France ; revised lectures (51-71). Springer Verlag. https://doi.org/10.1007/3-540-46583-9_3

Conference Paper

• Kutner, D. C., & Stewart, I. A. (2024, September). Reconfigurable routing in data center networks. Presented at 20th International Symposium on Algorithmics of Wireless Networks, ALGOWIN 2024, Egham, UK
• Friedetzky, T., Kutner, D., Mertzios, G., Stewart, I., & Trehan, A. (2023, January). Payment scheduling in the Interval Debt Model. Presented at 48th International Conference on Current Trends in Theory and Practice of Computer Science (SOFSEM 2023), Novy Smokovec, Slovakia
• Erickson, A., Kiasari, A., Navaridas, J., & Stewart, I. (2015, December). An efficient shortest path routing algorithm in the data centre network DPillar. Presented at 9th Annual International Conference on Combinatorial Optimization and Applications, COCOA, Houston, USA
• Stewart, I. (2015, August). On the mathematics of data centre network topologies. Presented at 20th International Symposium on Fundamentals of Computation Theory, Gdańsk, Poland
• Kiasari, A., Navaridas, J., & Stewart, I. (2015, December). Routing packets on DPillar data centre networks. Presented at 15th International Conference on Algorithms and Architectures for Parallel Processing, ICA3PP, Zhangjiajie, China
• Erickson, A., Kiasari, A., Navaridas, J., & Stewart, I. (2015, December). Routing algorithms for recursively-defined data centre networks. Presented at 13th IEEE International Symposium on Parallel and Distributed Processing with Applications, Helsinki
• Dawson, L., & Stewart, I. (2014, July). Accelerating ant colony optimization-based edge detection on the GPU using CUDA. Presented at 2014 IEEE Congress on Evolutionary Computation (CEC), Beijing, China
• Stewart, I. (2014, December). Improved routing in the data centre networks HCN and BCN. Presented at 2nd International Symposium on Computing and Networking - Across Practical Development and Theoretical Research, Shizuoka, Japan
• Golovach, P., Paulusma, D., & Stewart, I. A. (2013, December). Graph editing to a fixed target. Presented at International Workshop on Combinatorial Algorithms, Rouen, France
• Dawson, L., & Stewart, I. (2013, December). Improving Ant Colony Optimization performance on the GPU using CUDA. Presented at 2013 IEEE Congress on Evolutionary Computation, Cancun, Mexico
• Dawson, L., & Stewart, I. (2013, December). Candidate set parallelization strategies for Ant Colony Optimization on the GPU. Presented at 13th International Conference on Algorithms and Architectures for Parallel Processing, ICA3PP'13, Vietri sul Mare
• Xiang, Y., Stewart, I., & Madelaine, F. (2012, January). Node-to-node disjoint paths in k-ary n-cubes with faulty edges. Presented at 17th International Conference on Parallel and Distributed Systems, ICPADS'11., Tainan, Taiwan
• Stewart, I. (2011, December). Hamiltonian cycles through prescribed edges in k-ary n-cubes. Presented at 5th Annual International Conference on Combinatorial Optimization and Applications, COCOA'11., Zhangjiajie, China
• Zhao, J., Xiang, Y., Dawson, L., & Stewart, I. (2011, December). Color image edge detection based on quantity of color information and implementation on the GPU. Presented at 23rd IASTED International Conference on Parallel and Distributed Computing and Systems, PDCS'11., Dallas, USA
• Gate, J., & Stewart., I. (2010, June). Frameworks for logically classifying polynomial-time optimisation problems. Presented at 5th International Computer Science Symposium in Russia (CSR 2010), Kazan, Russia
• Stewart, I. (2010, April). A general algorithm for detecting faults under the comparison diagnosis model. Presented at 24th IEEE International Parallel and Distributed Processing Symposium (IPDPS 2010), Atlanta, Georgia, U.S.A
• Xiang, Y., & Stewart, I. (2009, December). Pancyclicity and panconnectivity in augmented k-ary n-cubes. Presented at The Fifteenth International Conference on Parallel and Distributed Systems : ICPADS'09, Shenzhen, China
• Xiang, Y., & Stewart, I. (2009, November). Pancyclicity in faulty k-ary 2-cubes. Presented at Proceedings of 21st International Conference on Parallel and Distributed Computing and Systems, PDCS'09., Cambridge, Massachusetts, USA
• Broersma, H., Johnson, M., Paulusma, D., & Stewart, I. (2006, March). The computational complexity of the parallel knock-out problem. Presented at 7th Latin American Theoretical Informatics Symposium (LATIN 2006), Valdivia, Chile
• Puricella, A., & Stewart, I. (2001, June). A generic greedy algorithm, partially-ordered graphs and NP-completeness. Presented at 27th International Workshop on Graph-Theoretic Concepts in Computer Science (WG 2001), Rostock, Germany

Journal Article

• Stewart, I., & Kutner, D. (2025). Reconfigurable routing in data center networks. Theoretical Computer Science, 1038, Article 115154. https://doi.org/10.1016/j.tcs.2025.115154
• Stewart, I., Kutner, D., Friedetzky, T., Trehan, A., & Mertzios, G. (2025). Payment Scheduling in the Interval Debt Model. Theoretical Computer Science, 1028, Article 115028. https://doi.org/10.1016/j.tcs.2024.115028
• Stewart, I. (2020). Using semidirect products of groups to build classes of interconnection networks. Discrete Applied Mathematics, 283, 78-97. https://doi.org/10.1016/j.dam.2019.12.014
• Stewart, I. (2020). Variational networks of cube-connected cycles are recursive cubes of rings. Information Processing Letters, 157, Article 105925. https://doi.org/10.1016/j.ipl.2020.105925
• Erickson, A., Navaridas, J., & Stewart, I. (2020). Relating the bisection width of dual-port, server-centric datacenter networks and the solution of edge-isoperimetric problems in graphs. Journal of Computer and System Sciences, 108, 10-28. https://doi.org/10.1016/j.jcss.2019.08.005
• Navaridas, J., Pascual, J. A., Erickson, A., Stewart, I. A., & Luján, M. (2019). INRFlow: An interconnection networks research flow-level simulation framework. Journal of Parallel and Distributed Computing, 130, 140-152. https://doi.org/10.1016/j.jpdc.2019.03.013
• Stewart, I., & Erickson, A. (2018). The influence of datacenter usage on symmetry in datacenter network design. Journal of Supercomputing, 74(6), 2276-2313. https://doi.org/10.1007/s11227-017-2217-1
• Stewart, I. (2017). On the combinatorial design of data centre network topologies. Journal of Computer and System Sciences, 89, 328-348. https://doi.org/10.1016/j.jcss.2017.05.015
• Erickson, A., Stewart, I., Pascual, J., & Navaridas, J. (2017). Improved routing algorithms in the dual-port datacenter networks HCN and BCN. Future Generation Computer Systems, 75, 58-71. https://doi.org/10.1016/j.future.2017.05.004
• Erickson, A., Stewart, I., Navaridas, J., & Kiasari, A. (2017). The stellar transformation: from interconnection networks to datacenter networks. Computer Networks, 113, 29-45. https://doi.org/10.1016/j.comnet.2016.12.001
• Golovach, P., Paulusma, D., & Stewart, I. (2017). Graph editing to a fixed target. Discrete Applied Mathematics, 216(Part 1), 181-190. https://doi.org/10.1016/j.dam.2014.07.008
• Stewart, I. (2016). Sufficient conditions for Hamiltonicity in multiswapped networks. Journal of Parallel and Distributed Computing, 101, 17-26. https://doi.org/10.1016/j.jpdc.2016.10.015
• Erickson, A., Kiasari, A., Navaridas, J., & Stewart, I. (2016). An Optimal Single-Path Routing Algorithm in the Datacenter Network DPillar. IEEE Transactions on Parallel and Distributed Systems, 28(3), 689-703. https://doi.org/10.1109/tpds.2016.2591011
• Kuo, C.-N., & Stewart, I. (2016). Edge-pancyclicity and edge-bipancyclicity of faulty folded hypercubes. Theoretical Computer Science, 627, 102-106. https://doi.org/10.1016/j.tcs.2016.02.029
• Stewart, I. (2014). Interconnection networks of degree three obtained by pruning two-dimensional tori. IEEE Transactions on Computers, 63(10), 2473-9340. https://doi.org/10.1109/tc.2013.139
• Stewart, I. (2013). Multiswapped networks and their topological and algorithmic properties. Journal of Computer and System Sciences, 79(8), 1269-1286. https://doi.org/10.1016/j.jcss.2013.06.002
• Gate, J., & Stewart, I. (2013). The expressibility of fragments of Hybrid Graph Logic on finite digraphs. Journal of applied logic, 11(3), 272-288. https://doi.org/10.1016/j.jal.2013.05.002
• Stewart, I. (2012). A general technique to establish the asymptotic conditional diagnosability of interconnection networks. Theoretical Computer Science, 452, 132-147. https://doi.org/10.1016/j.tcs.2012.05.015
• Stewart, I. (2012). On the computational complexity of routing in faulty k-ary n-cubes and hypercubes. Parallel Processing Letters, 22(1), Article 1250003. https://doi.org/10.1142/s012962641250003x
• Xiang, Y., & Stewart, I. (2011). Bipancyclicity in k-ary n-cubes with faulty edges under a conditional fault assumption. IEEE Transactions on Parallel and Distributed Systems, 22(9), 1506-1513. https://doi.org/10.1109/tpds.2011.22
• Xiang, Y., & Stewart, I. (2011). A multipath analysis of biswapped networks. The Computer Journal, 54(6), 920-930. https://doi.org/10.1093/comjnl/bxq083
• Xiang, Y., & Stewart, I. (2011). Augmented k-ary n-cubes. Information Sciences, 181(1), 239-256. https://doi.org/10.1016/j.ins.2010.09.005
• Lai, P.-L., Hsu, H.-C., Tsai, C.-H., & Stewart, I. (2010). A class of hierarchical graphs as topologies for interconnection networks. Theoretical Computer Science, 411(31-33), 2912-2924. https://doi.org/10.1016/j.tcs.2010.04.022
• Stewart, I., & Xiang, Y. (2010). One-to-many node-disjoint paths in (n,k)-star graphs. Discrete Applied Mathematics, 158(1), 62-70. https://doi.org/10.1016/j.dam.2009.08.013
• Arratia-Quesada, A., & Stewart, I. (2009). On the power of deep pushdown stacks. Acta Informatica, 46(7), 509-531. https://doi.org/10.1007/s00236-009-0103-x
• Stewart, I. (2009). Logical and complexity-theoretic aspects of models of computation with restricted access to arrays. Journal of Logic and Computation, 19(1), 217-242. https://doi.org/10.1093/logcom/exn025
• Stewart, I. (2009). Program schemes, queues, the recursive spectrum and zero-one laws. Fundamenta Informaticae, 91(2), 411-435. https://doi.org/10.3233/fi-2009-0050
• Stewart, I., & Xiang, Y. (2009). Bipanconnectivity and bipancyclicity in k-ary n-cubes. IEEE Transactions on Parallel and Distributed Systems, 20(1), 25-33. https://doi.org/10.1109/tpds.2008.45
• Madelaine, F., & Stewart, I. (2008). Improved upper and lower bounds on the feedback vertex numbers of grids and butterflies. Discrete Mathematics, 308(18), 4144-4164. https://doi.org/10.1016/j.disc.2007.08.007
• Stewart, I., & Xiang, Y. (2008). Embedding long paths in k-ary n-cubes with faulty nodes and links. IEEE Transactions on Parallel and Distributed Systems, 19(8), 1071-1085. https://doi.org/10.1109/tpds.2007.70787
• Stewart, I. (2008). On the fixed-parameter tractability of parameterized model-checking problems. Information Processing Letters, 106(1), 33-36. https://doi.org/10.1016/j.ipl.2007.09.009
• Broersma, H., Johnson, M., Paulusma, D., & Stewart, I. (2008). The computational complexity of the parallel knock-out problem. Theoretical Computer Science, 393(1-3), 182-195. https://doi.org/10.1016/j.tcs.2007.11.021
• Stewart, I. (2007). Distributed algorithms for building Hamiltonian cycles in k-ary n-cubes and hypercubes with faulty links. Journal of Interconnection Networks, 8(3), 253-284. https://doi.org/10.1142/s0219265907002016
• Madelaine, F., & Stewart, I. (2007). Constraint satisfaction, logic and forbidden patterns. SIAM Journal on Computing, 37(1), 132-163. https://doi.org/10.1137/050634840
• Gault, R., & Stewart, I. (2006). An infinite hierarchy in a class of polynomial-time program schemes. Theory of Computing Systems, 39(5), 753-783. https://doi.org/10.1007/s00224-005-1230-6
• Feder, T., Madelaine, F., & Stewart, I. (2004). Dichotomies for classes of homomorphism problems involving unary functions. Theoretical Computer Science, 314(1-2), 1-43. https://doi.org/10.1016/j.tcs.2003.12.015
• Stewart, I. (2003). The complexity of achievement and maintenance problems in agent-based systems. Artificial Intelligence, 146(2), 175-191. https://doi.org/10.1016/s0004-3702%2803%2900014-6
• Madelaine, F., & Stewart, I. (2003). Some problems not definable using structure homomorphisms. Ars combinatoria, 67, 153-159
• Stewart, I. (2003). Using program schemes to capture polynomial-time logically on certain classes of structures. LMS journal of computation and mathematics, 6, 40-67
• Arratia, A., & Stewart, I. (2003). A note on first-order projections and games. Theoretical Computer Science, 290(3), 2085-2093. https://doi.org/10.1016/s0304-3975%2802%2900491-7
• Puricella, A., & Stewart, I. (2003). Greedy algorithms, H-colourings and a complexity-theoretic dichotomy. Theoretical Computer Science, 290(3), 1897-1913. https://doi.org/10.1016/s0304-3975%2802%2900329-8
• Stewart, I. (2002). Program schemes, arrays, Lindström quantifiers and zero-one laws. Theoretical Computer Science, 275(1-2), 283-310. https://doi.org/10.1016/s0304-3975%2801%2900183-9
• Ashir, Y., & Stewart, I. (2002). Fault-tolerant embeddings of Hamiltonian circuits in k-ary n-cubes. SIAM Journal on Discrete Mathematics, 15(3), 317-328. https://doi.org/10.1137/s0895480196311183
• Gault, R., & Stewart, I. (2001). On a hierarchy involving transitive closure logic and existential second-order quantification. Logic Journal of the IGPL, 9(6), 769-780. https://doi.org/10.1093/jigpal/9.6.769
• Arratia-Quesada, A., Chauhan, S., & Stewart, I. (1999). Hierarchies in classes of program schemes. Journal of Logic and Computation, 9(6), 915-957. https://doi.org/10.1093/logcom/9.6.915
• Chauhan, S., & Stewart, I. (1999). On the power of built-in relations in certain classes of program schemes. Information Processing Letters, 69(2), 77-82. https://doi.org/10.1016/s0020-0190%2898%2900196-3