@conference {
	title = {Synchronization and Collision Avoidance in Non-Linear Flocking Networks of Autonomous Agents},
	author = {Somarakis, Christoforos., Paraskevas, Evripidis., Baras, John S., Motee, Nader.},
	year = {2016},
	month = {07/2016},
	abstract = {We introduce and discuss two novel second-order consensus networks with state-dependent couplings of CuckerSmale type. The first scheme models flocking to synchronization over a network of agents where the alignment of the agent{\textquoteright}s states occurs over a non-trivial limit orbit that is generated by the internal dynamics of each individual agent. The second scheme models the speed alignment of a group of agents which avoid approaching each other closer than a prescribed distance. While seemingly different, both of these systems can be analyzed using the same mathematical methods. We rigorously analyze both examples and reveal their striking similarities. We arrive at sufficient conditions that relate the initial configurations and the systems{\textquoteright} parameters that give rise to a collective common behavior. Simulation examples are presented to support our theoretical conclusions},
	address = {Athens, Greece},
	booktitle = {24th Mediterranean Conference on Control and Automation},
	pages = {pp. 1089-1094}
}
@conference {
	title = {Consensus and Synchronized Periodicity in Nonlinear Delayed Networks},
	author = {Somarakis, Christoforos., Baras, John S., Motee, Nader.},
	year = {2016},
	month = {07/2016},
	abstract = {In this paper, we investigate stability and convergence properties of a class of nonlinear delayed consensus networks. Using tools and techniques from functional differential equations, sufficient stability conditions with respect to a common state as well as estimates on the convergence rate are derived. We characterize the limit (consensus) state for time-invariant sub-classes of these networks. More importantly, we specify under what conditions a delayed network exhibits periodic synchronized solutions. We provide sufficient conditions for existence, uniqueness and stability of this interesting phenomenon that we illustrate with a simulation example.},
	address = {Minneapolis, Minnesota},
	booktitle = {22nd International Symposium on Mathematical Theory of Networks and Systems},
	pages = {pp. 823-829}
}
@conference {
	title = {The Effect of Delays in the Economic Dispatch Problem for Smart Grid Architectures},
	author = {Somarakis, Christoforos., Maity, Dipankar., Baras, John S.},
	year = {2016},
	month = {07/2016},
	abstract = {We consider the Economic Dispatch Problem~(EDP) in power systems for a smart-grid friendly environment.~We develop a consensus based decentralized optimization algorithm~that evolves in a time-varying communication network~that suffers from multiple propagation time-dependent delays.
This paper, being an improvisation of an earlier work of~ours, addresses the effects of time dependent delays in a fully~decentralized network. We show analytically and by simulation~that propagation delays may not only affect the performance~of the dynamic algorithm that solves the EDP but can ~also~destabilize the system.},
	address = {Boston, Massachusetts},
	booktitle = {2016 American Control Conference},
	pages = {pp. 3533-3538}
}
@conference {
	title = {Dynamics of Collectives with Opinionated Agents: The Case of Scrambling Connectivity},
	author = {Somarakis, Christoforos., Hadadi, R., Baras, John S.},
	year = {2016},
	month = {06/2016},
	abstract = {We investigate the problem of social/opinion networks of autonomous agents, each of which has a personal view that follows an independent dynamic behavior and it communicates with their neighbors under a cooperative algorithm. We apply mathematics from non-negative matrix theory. We investigate agents with identical and non-identical views and we establish sufficient conditions for stability and convergence to a common synchronized opinion.},
	address = {Aalborg, DK},
	booktitle = {European Control Conference (ECC16)},
	pages = {pp. 1445-1450}
}
@conference {
	title = {Distributed Solution of the Economic Dispatch Problem in Smart Grid Power Systems Framework with Delay},
	author = {Somarakis, Christoforos., Baras, John S.},
	year = {2015},
	month = {12/2015},
	abstract = {We consider the Economic Dispatch Problem in~power systems in a smart-grid architecture friendly environment.~The problem is tackled with the use of multiple decentralized~controllers that execute parallel distributed consensus~algorithms. The scenario takes into account the presence of~multiple time-varying communication delays.},
	address = {Osaka, Japan},
	booktitle = {54th Conference on Control (CDC 2015)},
	pages = {pp. 6577-6582}
}
@conference {
	title = {Non-Linear Flocking Networks with Collision Avoidance},
	author = {Somarakis, Christoforos., Baras, John S.},
	year = {2015},
	month = {07/2015},
	abstract = {We consider a second order non-linear consensus (flocking) network of a finite population of autonomous agents and~prove that the long-term behavior of its solution is towards a common value while the flock remains connected. We elevate the~analysis to a collision avoidance type flocking after taking into consideration repelling forces between agents.},
	address = {Hangzhou, China},
	booktitle = {34th Chinese Control Conference (CCC2015)},
	pages = {pp. 7633-7638}
}
@conference {
	title = {A Simple Proof of the Continuous Time Linear Consensus Problem with Applications in Non-Linear Flocking Networks},
	author = {Somarakis, Christoforos., Baras, John S.},
	year = {2015},
	month = {07/2015},
	abstract = {We revisit the linear distributed consensus problem~in continuous time, to provide a simple and elegant proof~under very mild assumptions. Our approach is based on a novel~extension of the contraction coefficient that can be adapted to~the continuous time version of the model. We apply our results~in non-linear second order consensus networks of Cucker-Smale type and we obtain new initial conditions for asymptotic~flocking.},
	address = {Linz, Austria},
	booktitle = {European Control Conference (ECC15)},
	pages = {pp. 1546-1553}
}
@conference {
	title = {New Results on Stochastic Consensus Networks},
	author = {Somarakis, Christoforos., Baras, John S.},
	year = {2015},
	month = {07/2015},
	abstract = {We revisit the general linear consensus problem and provide new conditions for asymptotic consensus on two types of stochastic versions of the algorithm, in discrete and continuous time. We show that our method unifies a number of proposed models in the literature as well as it extends and generalizes existing results.},
	address = {Maison de la Mutualite, Paris, France},
	booktitle = {2015 SIAM Conference on Control and Its Applications},
	pages = {pp. 115-122}
}
@conference {
	title = {Delay-independent convergence for Linear Consensus Networks with Applications to Non-linear Flocking Systems},
	author = {Somarakis, Christoforos., Baras, John S.},
	year = {2015},
	month = {06/2015},
	abstract = {This work studies a class of linear first order and non-linear second order static distributed consensus networks with time-varying multiple propagation delays, in continuous~time. We provide conditions for convergence of to a common constant value, under an increased~connectivity condition. The results are delay-independent in the sense that they hold for~arbitrary bounded delays. Our approach makes use of fundamental concepts from the Non-Negative Matrix Theory in a fairly elementary way.},
	address = {Ann Arbor, MI},
	booktitle = {12th IFAC Workshop on Time Delay Systems (TDS 2015)},
	pages = {pp. 159-164}
}
@conference {
	title = {Distributed Consensus Networks of Neutral Type},
	author = {Somarakis, Christoforos., Baras, John S.},
	year = {2015},
	month = {06/2015},
	abstract = {We propose and study a network of autonomous agents which evolve their state under a distributed consensus algorithm of non-linear neutral type. We provide sufficient conditions for convergence to a common consensus point, by means of a stability in variation argument and fixed point theory. Our approach provides both an estimation on the rate of convergence and an implicit expression for the consensus point.},
	address = {Torremolinos, Spain},
	booktitle = {23rd Mediterranean Conference on Control and Automoation (MED 2015)},
	pages = {pp. 1087-1092}
}
@conference {
	title = {Asymptotic Consensus Solutions in Non-Linear Delayed Distributed Algorithms Under Deterministic \& Stochastic Perturbations},
	author = {Somarakis, Christoforos., Baras, John S.},
	year = {2013},
	month = {12/2013},
	abstract = {We consider a multi-agent non-linear delayed model which sustains consensus type of solutions. We use fixed point theory arguments to establish sufficient conditions for existence and uniqueness of solutions that converge exponentially fast to a common value with prescribed rate. The conditions depend on the communication topology, the nonlinearity of the model as well as the delay in the propagation of information. Furthermore we test the robustness of our results in the presence of independent time varying perturbations both deterministic and stochastic.},
	address = {Florence, Italy},
	booktitle = {52nd IEEE Conference on Decision and Control},
	pages = {pp. 7821-7826}
}
@conference {
	title = {On The Convergence Rate of Non-Linear Consensus Networks with Delays},
	author = {Somarakis, Christoforos., Baras, John S.},
	year = {2013},
	month = {09/2013},
	abstract = {We consider a generic non-linear consensus model and prove convergence results to a common value together with prescribed rate of convergence. Instead of a Lyapunov approach we consider a functional metric space and make a fixed point theory argument using contraction mappings. We are restricted to the case of static networks.},
	address = {Toulouse, France},
	booktitle = {9th IFAC Symposium on Nonlinear Control Systems,},
	pages = {pp. 705-710}
}
@conference {
	title = {On the connectivity assumption of non-liner flocking models},
	author = {Somarakis, Christoforos., Baras, John S.},
	year = {2013},
	month = {08/2013},
	abstract = {The problem of collective behavior of autonomous agents is discussed. Based on state dependent communication graphs we analyze a family of nonlinear flocking models by establishing sufficient initial conditions so as connectivity and thus asymptotic flocking is ensured. We discuss models with non-linear uniformly bounded connection rates with and without delays.},
	address = {Mi{\k e}dzyzdroje, Poland},
	booktitle = {Proceedings of 8th International Conference on Methods and Models is Automation and Robotics (MMAR 2013)},
	pages = {pp. 800-805}
}
@conference {
	title = {On the connectivity of non-liner flocking models},
	author = {Somarakis, Christoforos., Baras, John S.},
	year = {2013},
	month = {08/2013},
	abstract = {The problem of collective behavior of autonomous agents is discussed. Based on state dependent communication graphs we analyze a family of nonlinear flocking models by establishing sufficient initial conditions so as connectivity and thus asymptotic flocking is ensured. We discuss models with non-linear uniformly bounded connection rates with and without delays.},
	address = {Mi{\k e}dzyzdroje, Poland},
	booktitle = {18th International Conference on Methods and Models is Automation and Robotics (MMAR 2013)},
	pages = {pp. 800-805}
}
@conference {
	title = {Fixed Point Theory Approach to Exponential Convergence in LTV Continuous Time Consensus Dynamics with Delays},
	author = {Somarakis, Christoforos., Baras, John S.},
	year = {2013},
	month = {07/2013},
	abstract = {The problem of continuous linear time varying consensus dynamics is addressed in the presence of constant communication delays. We make a Fixed Point Theory argument with the use of contraction mappings and we state sufficient conditions for exponential convergence to a consensus value with prescribed convergence rate.},
	address = {San Diego, CA},
	booktitle = {SIAM conference on Control and its Application 2013},
	pages = {pp. 129-136}
}
@conference {
	title = {LTI Continuous Time Consensus Dynamics with Multiple and Distributed Delays},
	author = {Somarakis, Christoforos., Baras, John S.},
	year = {2013},
	month = {06/2013},
	abstract = {We study linear time invariant (LTI) continuous time consensus dynamics in the presence of bounded communication delays. Contrary to traditional Lyapunov based methods, we approach the problem using Fixed Point Theory. This method, allows us to create an appropriate complete functional metric space and through contraction mappings to establish the existence and uniqueness of a solution of this model. We explore the case of constant as well as distributed delays.},
	address = {Platanias-Chania, Crete - GREECE},
	booktitle = {21st Mediterranean Conference on Control and Automation},
	pages = {pp. 1495-1501}
}
@conference {
	title = {A Randomized Gossip Consensus Algorithm on Convex Metric Spaces},
	author = {Matei, Ion., Somarakis, Christoforos., Baras, John S.},
	year = {2012},
	month = {12/2012},
	abstract = {A consensus problem consists of a group of dynamic agents who seek to agree upon certain quantities of interest. This problem can be generalized in the context of convex metric spaces that extend the standard notion of convexity. In this paper we introduce and analyze a randomized gossip algorithm for solving the generalized consensus problem on convex metric spaces. We study the convergence properties of the algorithm using stochastic differential equations theory. We show that the dynamics of the distances between the states of the agents can be upper bounded by the dynamics of a stochastic differential equation driven by Poisson counters. In addition, we introduce instances of the generalized consensus algorithm for several examples of convex metric spaces.},
	address = {Maui, Hawaii},
	booktitle = {51st IEEE Conference on Decision and Control,},
	pages = {pp. 7425-7430}
}
@conference {
	title = {The Consensus Problem Under Vanishing Communication Weights},
	author = {Somarakis, Christoforos., Baras, John S.},
	year = {2012},
	month = {07/2012},
	abstract = {We revisit the classical multi-agent distributed consensus problem under the dropping of the assumption that the existence of a connection between agent implies weights uniformly bounded away from zero. We formulate and study the problem by establishing global convergence results in discrete time, under fixed, switching and random topologies. We study the application of the results to flocking networks.},
	address = {Melbourne, Australia},
	booktitle = {20th International Symposium on Mathematical Theory of Networks and Systems (MTNS 2012)},
	pages = {pp. 1-8}
}
@conference {
	title = {On the complexity of a social behavior model},
	author = {Somarakis, Christoforos., Baras, John S.},
	year = {2011},
	month = {06/2011},
	abstract = {In this paper, we discuss a social behavior model in cellular automata. This model came as a result of research in dynamical structures of networks as these were constructed out of game theory and statistical physics. We define it a dynamical system on the planar grid and study its behavior by varying its parameters under different initial configurations.},
	address = {Quincy, MA},
	booktitle = {Eighth International Conference on Complex Systems (ICCS 2011)},
	pages = {pp.  1330-1344},
	organization = {Boston Marriott}
}
@conference {
	title = {Chaos On A Simple Rational Planar Map},
	author = {Somarakis, Christoforos., Baras, John S.},
	year = {2011},
	month = {05/2011},
	abstract = {The dynamics of a 2-D rational map are studied for various values of it{\textquoteright}s control parameters. Despite it{\textquoteright}s simple structure this model is very rich in non-linear phenomena such as, multi-scroll strange attractors, transitions to chaos via period doubling bifurcations, quasi-periodicity as well as intermittency, interior crisis, hyper-chaos etc. In this work, strange attractors, bifurcation diagrams, periodic indows, invariant characteristics are investigated both analytically and numerically.},
	address = {Crete, Greece},
	booktitle = {4th Chaotic Modeling and Simulation International Conference (CHAOS 2011)},
	pages = {pp. 1-9},
	organization = {Agios Nikolaos }
}
@article {
	title = {Convergence Analysis of Classes of Asymmetric Networks of Cucker-Smale Type with Deterministic Perturbations},
	author = {Somarakis, Christoforos., Paraskevas, Evripidis., Baras, John S., Motee, Nader.},
	year = {2017},
	month = {10/2017},
	abstract = {We discuss two nonlinear perturbed extensions of the Cucker-Smale model with asymmetric coupling weights. The first model assumes a finite collection of autonomous agents aiming to perform a consensus process in the presence of identical internal dynamics. The second model describes a similar population of agents that perform velocity alignment with the restriction of collision-free orbits. Although qualitatively different, we explain how these two non-trivial types of perturbations are analyzed under a unified framework. Rigorous analysis is conducted towards establishing sufficient conditions for asymptotic flocking to a synchronized motion. Applications of our results are compared with simulations to illustrate the effectiveness of our theoretical estimates.},
	pages = {pp. 1-11},
	journal = {IEEE transactions on control of network systems}
}
@article {
	title = {A Generalized Gossip Algorithm on Convex Metric Spaces},
	author = {Matei, Ion., Somarakis, Christoforos., Baras, John S.},
	year = {2015},
	month = {05/2015},
	abstract = {A consensus problem consists of a group of dynamic agents who seek to agree upon certain quantities of interest. This problem can be generalized in the context of convex metric spaces that extend the standard notion of convexity. In this paper, we introduce and analyze a randomized gossip algorithm for solving the generalized consensus problem on convex metric spaces, where the communication between agents is based on a set of Poisson counters. We study the convergence properties of the algorithm using stochastic differential equations theory. In particular, we show that the distances between the states of the agents converge to zero with probability one and in the rth mean sense. In the special case of complete connectivity and uniform Poisson counters, we give upper bounds on the dynamics of the first and second moments of the distances between the states of the agents. In addition, we introduce instances of the generalized consensus algorithm for several examples of convex metric spaces together with numerical simulations. th~mean sense. In the special case of complete connectivity and uniform Poisson counters, we give upper bounds on the dynamics of the first and second moments of the distances between the states of the agents. In addition, we introduce instances of the generalized consensus algorithm for several examples of convex metric spaces together with numerical simulations.},
	pages = {pp. 1175 - 1187},
	volume = {Vol. 60},
	number = {No. 5},
	journal = {IEEE Transactions on Automatic Control.}
}
@techreport {
	title = {On the dynamics of linear functional differential equations with asymptotically constant solutions},
	author = {Somarakis, Christoforos., Baras, John S., Paraskevas, Evripidis.},
	year = {2015},
	month = {01/2015},
	abstract = {We discuss the dynamics of general linear functional differential equations with solutions that exhibit asymptotic constancy. We apply fixed point theory methods to study the stability of these solutions and we provide sufficient conditions of asymptotic stability with emphasis on the rate of convergence. Several examples are provided to illustrate the claim that the derived results generalize, unify and in some cases improve the existing ones.}
}
@techreport {
	title = {Stability by Fixed Point Theory in Time Delayed Distributed Consensus Networks},
	author = {Somarakis, Christoforos., Baras, John S., Paraskevas, Evripidis.},
	year = {2014},
	month = {09/2014},
	abstract = {We study the stability of linear time invariant distributed consensus dynamics in the presence of multiple propagation and processing delays. We employ fixed point theory (FPT) methods and derive sufficient conditions for asymptotic convergence to a common value while the emphasis is given in estimating the rate of convergence. We argue that this approach is novel in the field of networked dynamics as it is also flexible and thus capable of analyzing a wide variety of consensus based algorithms for which conventional Lyapunov methods are either too restrictive or unsuccessful.}
}
@article {
	title = {On the Dynamics of a Simple Rational Planar Map},
	author = {Somarakis, Christoforos., Baras, John S.},
	year = {2013},
	month = {06/2013},
	abstract = {are discussed for various values of it{\textquoteright}s parameters. Despite the simple algebraic structure, this map, recently introduced in the literature, is very rich in non-linear phenomena. Multiple strange attractors, transitions to chaos via period doubling bifurcations, quasiperiodicity as well as intermittency, interior crisis, hyper-chaos are only a few. In this work, strange attractors, bifurcation diagrams, periodic windows, invariant characteristics are investigated both analytically and numerically.},
	pages = {pp. 1330021.1-1330021.21},
	volume = {Vol. 23},
	number = {Issue 6},
	journal = {International Journal of Bifurcation and Chaos (IJBC)}
}
@techreport {
	title = {A Fixed Point Theory Approach to Multi-Agent Consensus Dynamics With Delays},
	author = {Somarakis, Christoforos., Baras, John S.},
	year = {2013},
	month = {02/2013},
	abstract = {The classic linear time-invariant multi-agent consensus scheme is revisited in the presence of constant and distributed bounded delays. We create a fixed point argument and prove exponential convergence with specific rate that depends both on the topology of the communication graph and the upper bound of the allowed delay.}
}
@article {
	title = {Convergence Results for the Linear Consensus Problem under Markovian Random Graphs},
	author = {Matei, Ion., Baras, John S., Somarakis, Christoforos.},
	year = {2013},
	month = {01/2013},
	abstract = {This paper discusses the linear asymptotic consensus problem for a network of dynamic agents whose communication network is modeled by a randomly switching graph. The switching is determined by a finite state Markov process, each topology corresponding to a state of the process. We address the cases where the dynamics of the agents is expressed both in continuous time and in discrete time. We show that, if the consensus matrices are doubly stochastic, average consensus is achieved in the mean square sense and the almost sure sense if and only if the graph resulting from the union of graphs corresponding to the states of the Markov process is strongly connected. The aim of this paper is to show how techniques from the theory of Markovian jump linear systems, in conjunction with results inspired by matrix and graph theory, can be used to prove convergence results for stochastic consensus problems.},
	pages = {pp. 1574-1591},
	volume = {Vol.  51},
	number = {No. 2},
	journal = {SIAM Journal on Control and Optimization}
}
@techreport {
	title = {A randomized gossip consensus algorithm on convex metric spaces},
	author = {Matei, Ion., Somarakis, Christoforos., Baras, John S.},
	year = {2012},
	month = {02/2012},
	abstract = {A consensus problem consists of a group of dynamic agents who seek to agree upon certain quantities of interest. This problem can be generalized in the context of convex metric spaces that extend the standard notion of convexity. In this paper we introduce and analyze a randomized gossip algorithm for solving the generalized consensus problem on convex metric spaces. We study the convergence properties of the algorithm using stochastic differential equations theory. We show that the dynamics of the distances between the states of the agents can be upper bounded by the dynamics of a stochastic differential equation driven by Poisson counters. In addition, we introduce instances of the generalized consensus algorithm for several examples of convex metric spaces together with numerical simulations.}
}
