# Antonis

### From SYSOS

# Biographical Sketch

In 2000 I obtained an MA/MEng degree in Electrical and Information Sciences from the University of Cambridge, U.K., as a member of Robinson College. In 2005 I completed a PhD in Control and Dynamical Systems at the California Institute of Technology, with a PhD Minor in Aeronautics. My thesis was on the "Scalable Analysis of Nonlinear Systems Using Convex Optimization" and was under the supervision of Professor John C. Doyle. After a short David Crighton Fellowship at the University of Cambridge and a postdoctoral fellowship at the California Institute of Technology, I joined the Department of Engineering Science at the University of Oxford as a Departmental Lecturer in Control Engineering in January 2006.

# Research Interests

- Modern Control Theory, Robust Stability Analysis and Design.
- Nonlinear Dynamical Systems, Lyapunov stability.
- Convex optimization (Linear and Semidefinite Programming, LMIs). Sum of Squares programming.
- Systems and Synthetic Biology.
- Networked systems: Multi-agent systems, consensus, flocking, alignment. Synchronization of oscillator networks. Internet congestion Control. Population dynamic systems. Biochemical Reaction Networks.
- Aerospace systems and flow control.

# Publications

## Systems Biology

- M. A. J. Roberts, E. August, A. Hamadeh, P. K. Maini, P. E. McSharry, J. P. Armitage and A. Papachristodoulou. A model invalidation-based approach for elucidating biological signalling pathways, applied to the chemotaxis pathway in
*R. sphaeroides*. BMC Systems Biology 2009, 3:105. [1] - J. Anderson and A. Papachristodoulou. On Validation and Invalidation of Biological Models. BMC Bioinformatics 2009, 10:132. [2]
- E. August and A. Papachristodoulou. Efficient, sparse biological network determination. BMC Systems Biology 2009, 3:25. [3]
- E. August and A. Papachristodoulou. A new computational tool for establishing model parameter identifiability. Journal of Computational Biology. June 2009, 16(6): 875-885. [4]
- E. August, A. Papachristodoulou, B. Recht, M. A. J. Roberts and A. Jadbabaie. Determining Interconnections in Biochemical Networks Using Linear Programming. In Proc. of the IEEE CDC, 2008. [5]
- A. Papachristodoulou and B. Recht. Determining Interconnections in Chemical Reaction Networks. In Proc. of the American Control Conference, 2007. [6]
- A. Papachristodoulou and H. El-Samad. Algorithms for Discriminating between Biochemical Reaction Network Models: Towards Systematic Experimental Design. In Proc. of the American Control Conference, 2007. [7]
- H. El-Samad, S. Prajna, A. Papachristodoulou, J. C. Doyle, and M. Khammash. Advanced Methods and Algorithms for Biological Networks Analysis. Proceedings of the IEEE, 94(4): 832 – 853, 2006. [8]
- H. El-Samad, M. Fazel, X. Liu, A. Papachristodoulou, S. Prajna. Stochastic Reachability Analysis in Complex Biological Networks. In Proc. of the American Control Conference, 2006. [9]
- T.-M. Yi, M. Fazel, X. Liu, O. Otitoju, J. Gonçalves, A. Papachristodoulou, S. Prajna, J. C. Doyle. Application of Robust Model Validation Using SOSTOOLS to the Study of G-Protein Signaling in Yeast. In Proc. of Foundations of Systems Biology in Engineering, 2005.
- H. El-Samad, S. Prajna, A. Papachristodoulou, M. Khammash, and J.C. Doyle. Model validation and robust stability analysis of the bacterial heat shock response using SOSTOOLS. In Proc. of the IEEE CDC, 2003. [10]

## Sum of Squares Techniques

- J. Anderson and A. Papachristodoulou. A Network Decomposition Approach for Efficient Sum-of-Squares Programming Based Analysis. In Proceedings of the American Control Conference, 2010.
- M. Peet and A. Papachristodoulou. Inverses of Positive Linear Operators and State Feedback Design for Time-Delay Systems. In Proceedings of the 8th IFAC Workshop on Time Delay Systems, 2009.
- A. Papachristodoulou and S. Prajna. Robust stability analysis of nonlinear hybrid systems. IEEE Transactions on Automatic Control. Volume 54, Issue 5, pp. 1037-1043 (2009) [11]
- A. Papachristodoulou, M. M. Peet and S. Lall. Analysis of polynomial systems with time delays via the sum of squares decomposition. IEEE Transactions on Automatic Control. Volume 54, Issue 5, 1061-1067 (2009) [12]
- M. M. Peet, A. Papachristodoulou and S. Lall. Positive forms and stability of linear time-delay systems. SIAM J. Control Optim. Volume 47, Issue 6, pp. 3237-3258 (2009) [13]
- M. M. Peet and A. Papachristodoulou. Using polynomial semi-separable kernels to construct infinite-dimensional Lyapunov functions. In Proc. of the IEEE CDC, 2008.
- A. Papachristodoulou, M. M. Peet and S.-I. Niculescu. Stability Analysis of Linear Systems with Time-Varying Delays: Delay Uncertainty and Quenching. In Proc. of the IEEE CDC, 2007.
- M. M. Peet and A. Papachristodoulou. Positivity of Kernel Functions for Systems with Communication Delay. In Proc. of the IEEE CDC, 2007.
- M. M. Peet, A. Papachristodoulou, and S. Lall. Positive Forms and Stability of Linear Time-Delay Systems. In Proc. of the IEEE CDC, 2006.
- A. Papachristodoulou and M. M. Peet. On the Analysis of Systems Described by Classes of Partial Differential Equations. In Proc. of the IEEE CDC, 2006.
- A. A. Salinas-Varela, A. Papachristodoulou and J. Gonçalves. On L2 Error Bounds between Systems. In Proc. of the International Symposium on Mathematical Theory of Networks and Systems, 2006.
- A. Papachristodoulou. Robust stabilization of nonlinear time delay systems using convex optimization. In Proc. of the IEEE CDC, 2005.
- A. Papachristodoulou, M. M. Peet and S. Lall. Constructing Lyapunov-Krasovskii Functionals for Linear Time Delay Systems. In Proc. of the American Control Conference, 2005.
- A. Papachristodoulou and S. Prajna. Analysis of non-polynomial systems using the sum of squares decomposition. In Positive Polynomials in Control, Springer-Verlag, 2005.
- S. Prajna, A. Papachristodoulou, and F. Wu. Nonlinear control synthesis by sum of squares optimization: A Lyapunov-based approach. In Proc. of the Asian Control Conference, 2004.
- A. Papachristodoulou. Analysis of nonlinear time delay systems using the sum of squares decomposition. In Proc. of the American Control Conference, 2004.
- S. Prajna and A. Papachristodoulou. Analysis of switched and hybrid systems – beyond piecewise quadratic methods. In Proc. of the American Control Conference, 2003.
- A. Papachristodoulou and S. Prajna. On the construction of Lyapunov functions using the sum of squares decomposition. In Proc. of the IEEE CDC, 2002.

## Large Scale Systems Analysis and Design

- A. Papachristodoulou, A. Jadbabaie and U. Münz. Effects of Delay in Multi-Agent Consensus and Oscillator Synchronization. IEEE Transactions on Automatic Control, July 2010.
- A. Papachristodoulou and A. Jadbabaie. Delay Robustness of Nonlinear Internet Congestion Control Schemes. IEEE Transactions on Automatic Control, June 2010.
- U. Münz, A. Papachristodoulou, and F. Allgöwer. Robust Rendezvous of Heterogeneous Langrange Systems on Packet-Switched Networks. at - Automatisierungstechnik, April 2010.
- U. Münz, A. Papachristodoulou and F. Allgöwer. Generalized Nyquist Consensus Condition for Large High-Order Linear Multi-Agent Systems with Communication Delays. In Proceedings of the IEEE Conference on Decision and Control, 2009.
- J. Anderson and A. Papachristodoulou. A Decomposition/Synchronization Scheme for Formulating and Solving Optimization Problems. In Proceedings of the 1st IFAC workshop on distributed estimation and control in networked systems, 2009.
- U. Münz, A. Papachristodoulou and F. Allgöwer. Generalized Nyquist Consensus Condition for Linear Multi-Agent Systems with Heterogeneous Delays. In Proceedings of the 1st IFAC workshop on distributed estimation and control in networked systems, 2009.
- U. Münz, A. Papachristodoulou and F. Allgöwer. Output Consensus Controller Design for Nonlinear Relative Degree One Multi-Agent Systems with Delays. In Proceedings of the 8th IFAC Workshop on Time Delay Systems, 2009.
- U. Münz, A. Papachristodoulou and F. Allgöwer. Consensus Reaching in Multi-Agent Packet-Switched Networks with Nonlinear Coupling. International Journal of Control, Volume 82, Issue 5, May 2009, pages 953 - 969. [14]
- U. Münz, A. Papachristodoulou and F. Allgöwer. Delay-dependent rendezvous and flocking of large scale multi-agent systems with communication delays. In Proc. of the IEEE CDC, 2008.
- U. Münz, A. Papachristodoulou and F. Allgöwer. Nonlinear Multi-Agent System Consensus with Time-Varying Delays. In Proc. of the IFAC World Congress, 2008.
- A. Papachristodoulou and M. M. Peet. Global Stability Analysis of Primal Internet Congestion Control Schemes with Heterogeneous Delays. In Proc. of the IFAC World Congress, 2008.
- Y. Li, A. Papachristodoulou, M. Chiang and A. R. Calderbank. Stability of Congestion Control Schemes with Delay Sensitive Traffic. In Proc. of the American Control Conference, 2008.
- U. Münz, A. Papachristodoulou and F. Allgöwer. Multi-Agent System Consensus in Packet-Switched Networks. Proc. of the European Control Conference, 2007.
- A. Papachristodoulou, A. Jadbabaie. Synchronization in Oscillator Networks with Heterogeneous Delays, Switching Topologies and Nonlinear Dynamics. In Proc. of the IEEE CDC, 2006.
- A. Papachristodoulou, A. Jadbabaie. Synchronization in Oscillator Networks: Switching Topologies and Non-homogeneous Delays. In Proc. of the IEEE CDC, 2005.
- A. Papachristodoulou, L. Li and J. C. Doyle. Methodological Frameworks for Large-scale Network Analysis and Design. ACM SIGCOMM Comp. Comm. Reviews, 34(3): 7 – 20, 2004.
- A. Papachristodoulou. Global stability analysis of a TCP/AQM protocol for arbitrary networks with delay. In Proc. of the IEEE CDC, 2004.

## Software

- S. Prajna, A. Papachristodoulou, and P. A. Parrilo. SOSTOOLS – Sum of Squares Optimization Toolbox, User’s Guide. Available at http://www.eng.ox.ac.uk/control/sostools, 2002.
- S. Prajna, A. Papachristodoulou, and P. A. Parrilo. Introducing SOSTOOLS: A general purpose sum of squares programming solver. In Proc. of the IEEE CDC, 2002.
- S. Prajna, A. Papachristodoulou, P. Seiler, and P. A. Parrilo. SOSTOOLS and its Control Applications. In Positive Polynomials in Control, Springer-Verlag, 2005.

## Applications

- A. Papachristodoulou and M. M. Peet. SOS for Nonlinear Delayed Models in Biology and Networking. In Topics in Time-Delay Systems: Analysis, Algorithms and Control, Springer-Verlag, 2008.
- S. Glavaski, D. Subramanian, K. Ariyur, R. Ghosh, N. Lamba and A. Papachristodoulou. A Nonlinear Hybrid Life Support System: Dynamic Modelling, Control Design, and Safety Verification. IEEE Transactions on Control Technology, 15(6): 1003 – 1017, 2007.
- A. Papachristodoulou, S. Prajna and S. Glavaski. Sum of Squares in Industry: An Algorithmic Analysis Approach. Tutorial Session at the American Control Conference, 2005.
- K. Krishnaswamy, G. Papageorgiou, S. Glavaski, and A. Papachristodoulou. Analysis of aircraft pitch axis stability augmentation system using sum of squares optimization. In Proc. of the American Control Conference, 2005.
- A. Papachristodoulou and C. Papageorgiou. Robust stability and performance analysis of a longitudinal aircraft model using sum of squares techniques. In Proc. of the Mediterranean Control Conference, 2005.
- S. Glavaski, A. Papachristodoulou and K. Ariyur. Computational challenges of controlled hybrid system safety verification. In Hybrid Systems: Computation and Control, Springer-Verlag, 2005.
- A. Papachristodoulou, J. C. Doyle, and S. H. Low. Analysis of nonlinear delay differential equation models of TCP/AQM protocols using sums of squares. In Proc. of the IEEE CDC, 2004.
- A. Papachristodoulou and F. E. C. Culick. Flight Mechanics of the Wright Aircraft 1903-1912. In AIAA 41st Aerospace Sciences Meeting and Exhibit, Paper number AIAA-2003-0097, 2003.

## Theses

- A. Papachristodoulou. Scalable Analysis of Nonlinear Systems Using Convex Optimization. PhD Thesis, California Institute of Technology, Pasadena CA, 2005.

# Teaching

- Academic Year 2006-2007
- Michaelmas 2006: C5A, Control and Optimization of Operations
- Hilary 2007: C4A, Networked Systems

- Academic Year 2007-2008
- Michaelmas 2007: C4A, Networked Systems
- Hilary 2008: C5B, Biosystem Modelling

- Academic Year 2008-2009
- Hilary 2009: C4A: Networked Systems, C5B: Biosystem Modelling.

- Academic Year 2009-2010
- Hilary 2010: C4A: Networked Systems, C5B: Biosystem Modelling.

# Contact Info

- E-mail: antonis at eng point ox point ac point uk

- Department Address: Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, U.K. Telephone: +44 1865 2 83036

- College Address: St Edmund Hall, Oxford OX1 4AR, U.K.