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Journal ArticleDOI

Stability of multiagent systems with time-dependent communication links

14 Feb 2005-IEEE Transactions on Automatic Control (IEEE)-Vol. 50, Iss: 2, pp 169-182
TL;DR: It is observed that more communication does not necessarily lead to faster convergence and may eventually even lead to a loss of convergence, even for the simple models discussed in the present paper.
Abstract: We study a simple but compelling model of network of agents interacting via time-dependent communication links. The model finds application in a variety of fields including synchronization, swarming and distributed decision making. In the model, each agent updates his current state based upon the current information received from neighboring agents. Necessary and/or sufficient conditions for the convergence of the individual agents' states to a common value are presented, thereby extending recent results reported in the literature. The stability analysis is based upon a blend of graph-theoretic and system-theoretic tools with the notion of convexity playing a central role. The analysis is integrated within a formal framework of set-valued Lyapunov theory, which may be of independent interest. Among others, it is observed that more communication does not necessarily lead to faster convergence and may eventually even lead to a loss of convergence, even for the simple models discussed in the present paper.
Citations
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Journal ArticleDOI
05 Mar 2007
TL;DR: A theoretical framework for analysis of consensus algorithms for multi-agent networked systems with an emphasis on the role of directed information flow, robustness to changes in network topology due to link/node failures, time-delays, and performance guarantees is provided.
Abstract: This paper provides a theoretical framework for analysis of consensus algorithms for multi-agent networked systems with an emphasis on the role of directed information flow, robustness to changes in network topology due to link/node failures, time-delays, and performance guarantees. An overview of basic concepts of information consensus in networks and methods of convergence and performance analysis for the algorithms are provided. Our analysis framework is based on tools from matrix theory, algebraic graph theory, and control theory. We discuss the connections between consensus problems in networked dynamic systems and diverse applications including synchronization of coupled oscillators, flocking, formation control, fast consensus in small-world networks, Markov processes and gossip-based algorithms, load balancing in networks, rendezvous in space, distributed sensor fusion in sensor networks, and belief propagation. We establish direct connections between spectral and structural properties of complex networks and the speed of information diffusion of consensus algorithms. A brief introduction is provided on networked systems with nonlocal information flow that are considerably faster than distributed systems with lattice-type nearest neighbor interactions. Simulation results are presented that demonstrate the role of small-world effects on the speed of consensus algorithms and cooperative control of multivehicle formations

9,715 citations


Cites background or methods from "Stability of multiagent systems wit..."

  • ...Recently, an extension of Theorem 6 with connectivity of the union of graphs over an infinite interval has been introduced by Moreau [14] (also, an extension is presented in [15] for weighted graphs)....

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  • ...Proof: See the proof of Proposition 2 in [14]....

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  • ...In this paper, we focus on the work described in five key papers—namely, Jadbabaie, Lin, and Morse [38], Olfati-Saber and Murray [70], Fax and Murray [28], Moreau [59], and Ren and Beard [74]— that have been instrumental in paving the way for more recent advances in study of self-organizing networked systems, or swarms....

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  • ...Here, we rephrase a theorem due to Moreau and present it based our notation....

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  • ...h Similarly, the algorithm analyzed in Proposition 2 of [14] does not solve the f -consensus problem....

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Journal ArticleDOI
TL;DR: It is shown that information consensus under dynamically changing interaction topologies can be achieved asymptotically if the union of the directed interaction graphs have a spanning tree frequently enough as the system evolves.
Abstract: This note considers the problem of information consensus among multiple agents in the presence of limited and unreliable information exchange with dynamically changing interaction topologies. Both discrete and continuous update schemes are proposed for information consensus. This note shows that information consensus under dynamically changing interaction topologies can be achieved asymptotically if the union of the directed interaction graphs have a spanning tree frequently enough as the system evolves.

6,135 citations

Journal ArticleDOI
TL;DR: A theoretical framework for design and analysis of distributed flocking algorithms, and shows that migration of flocks can be performed using a peer-to-peer network of agents, i.e., "flocks need no leaders."
Abstract: In this paper, we present a theoretical framework for design and analysis of distributed flocking algorithms. Two cases of flocking in free-space and presence of multiple obstacles are considered. We present three flocking algorithms: two for free-flocking and one for constrained flocking. A comprehensive analysis of the first two algorithms is provided. We demonstrate the first algorithm embodies all three rules of Reynolds. This is a formal approach to extraction of interaction rules that lead to the emergence of collective behavior. We show that the first algorithm generically leads to regular fragmentation, whereas the second and third algorithms both lead to flocking. A systematic method is provided for construction of cost functions (or collective potentials) for flocking. These collective potentials penalize deviation from a class of lattice-shape objects called /spl alpha/-lattices. We use a multi-species framework for construction of collective potentials that consist of flock-members, or /spl alpha/-agents, and virtual agents associated with /spl alpha/-agents called /spl beta/- and /spl gamma/-agents. We show that migration of flocks can be performed using a peer-to-peer network of agents, i.e., "flocks need no leaders." A "universal" definition of flocking for particle systems with similarities to Lyapunov stability is given. Several simulation results are provided that demonstrate performing 2-D and 3-D flocking, split/rejoin maneuver, and squeezing maneuver for hundreds of agents using the proposed algorithms.

4,693 citations


Cites background from "Stability of multiagent systems wit..."

  • ...Recently, there has been a surge of interest among control scientists in consensus problems due to the work of Olfati-Saber and Murray [20], [21] and alignment on networks with variable topology by Jadbabaie et al. [22], Moreau [23], and Ren and Beard [24]....

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  • ...[22], Moreau [23], and Ren and Beard [24]....

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Journal ArticleDOI
TL;DR: Theoretical results regarding consensus-seeking under both time invariant and dynamically changing communication topologies are summarized in this paper, where several specific applications of consensus algorithms to multivehicle coordination are described.
Abstract: The purpose of this article is to provide a tutorial overview of information consensus in multivehicle cooperative control. Theoretical results regarding consensus-seeking under both time invariant and dynamically changing communication topologies are summarized. Several specific applications of consensus algorithms to multivehicle coordination are described

3,028 citations


Cites background or methods or result from "Stability of multiagent systems wit..."

  • ...Using set-valued Lyapunov theory, [ 31 ] shows that the discrete-time consensus algorithm (S3) is uniformly globally attractive with respect to the collection of equilibrium solutions span{1} if and only if there exists K ≥ 0 such that the union of the communication graphs has a rooted directed spanning tree across each interval of length Kh, where h is the sample time....

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  • ...The most common discrete-time consensus algorithm has the form [S3], [24], [26], [ 31 ]...

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  • ...In addition, the result in [ 31 ] is extended to take into account bounded time delays in [40]....

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  • ...Lyapunov Analysis of Consensus Algorithms Nonlinear analysis tools can also be used to study consensus algorithms [ 31 ]....

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  • ...shown in [ 31 ] that V(t2) ⊆ V(t1) for all t2 ≥ t1, and that x(t) approaches an element of the set span{1}, which implies that consensus is reached....

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Journal ArticleDOI
TL;DR: This work considers the problem of finding a linear iteration that yields distributed averaging consensus over a network, i.e., that asymptotically computes the average of some initial values given at the nodes, and gives several extensions and variations on the basic problem.

2,692 citations


Cites methods from "Stability of multiagent systems wit..."

  • ...Related coordination problems with time-varying topologies have been studied in [21] using a switched linear system model, and in [27] using set-valued Lyapunov theory....

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References
More filters
Journal ArticleDOI
TL;DR: A distinctive feature of this work is to address consensus problems for networks with directed information flow by establishing a direct connection between the algebraic connectivity of the network and the performance of a linear consensus protocol.
Abstract: In this paper, we discuss consensus problems for networks of dynamic agents with fixed and switching topologies. We analyze three cases: 1) directed networks with fixed topology; 2) directed networks with switching topology; and 3) undirected networks with communication time-delays and fixed topology. We introduce two consensus protocols for networks with and without time-delays and provide a convergence analysis in all three cases. We establish a direct connection between the algebraic connectivity (or Fiedler eigenvalue) of the network and the performance (or negotiation speed) of a linear consensus protocol. This required the generalization of the notion of algebraic connectivity of undirected graphs to digraphs. It turns out that balanced digraphs play a key role in addressing average-consensus problems. We introduce disagreement functions for convergence analysis of consensus protocols. A disagreement function is a Lyapunov function for the disagreement network dynamics. We proposed a simple disagreement function that is a common Lyapunov function for the disagreement dynamics of a directed network with switching topology. A distinctive feature of this work is to address consensus problems for networks with directed information flow. We provide analytical tools that rely on algebraic graph theory, matrix theory, and control theory. Simulations are provided that demonstrate the effectiveness of our theoretical results.

11,658 citations

Journal ArticleDOI
TL;DR: A theoretical explanation for the observed behavior of the Vicsek model, which proves to be a graphic example of a switched linear system which is stable, but for which there does not exist a common quadratic Lyapunov function.
Abstract: In a recent Physical Review Letters article, Vicsek et al. propose a simple but compelling discrete-time model of n autonomous agents (i.e., points or particles) all moving in the plane with the same speed but with different headings. Each agent's heading is updated using a local rule based on the average of its own heading plus the headings of its "neighbors." In their paper, Vicsek et al. provide simulation results which demonstrate that the nearest neighbor rule they are studying can cause all agents to eventually move in the same direction despite the absence of centralized coordination and despite the fact that each agent's set of nearest neighbors change with time as the system evolves. This paper provides a theoretical explanation for this observed behavior. In addition, convergence results are derived for several other similarly inspired models. The Vicsek model proves to be a graphic example of a switched linear system which is stable, but for which there does not exist a common quadratic Lyapunov function.

8,233 citations


"Stability of multiagent systems wit..." refers background or methods or result in this paper

  • ...topology guaranteeing convergence of the individual agents’ states to a common value, thereby extending some of the results reported in [14], [27]–[29], and [31]....

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  • ...The approach of the present paper applies to the linear swarming model of [14] as well as to the nonlinear model of [11] provided the initial orientation differences are sufficiently small....

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  • ...Other studies that consider the connection between communication topology and system stability such as [14], [27]–[29], [31], [34], and [35] typically rely on algebraic graph theory, relating the graph topology with the algebraic structure of associated graph matrices....

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  • ...1Within the context of swarming models [11], [14], agent i could be a particle moving at constant speed in two-dimensional space and x could represent its heading....

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  • ...This is the swarming model studied in [14] and corresponds to the linear example of Section II with all weights equal to 1....

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Journal ArticleDOI
TL;DR: Numerical evidence is presented that this model results in a kinetic phase transition from no transport to finite net transport through spontaneous symmetry breaking of the rotational symmetry.
Abstract: A simple model with a novel type of dynamics is introduced in order to investigate the emergence of self-ordered motion in systems of particles with biologically motivated interaction. In our model particles are driven with a constant absolute velocity and at each time step assume the average direction of motion of the particles in their neighborhood with some random perturbation $(\ensuremath{\eta})$ added. We present numerical evidence that this model results in a kinetic phase transition from no transport (zero average velocity, $|{\mathbf{v}}_{a}|\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0$) to finite net transport through spontaneous symmetry breaking of the rotational symmetry. The transition is continuous, since $|{\mathbf{v}}_{a}|$ is found to scale as $({\ensuremath{\eta}}_{c}\ensuremath{-}\ensuremath{\eta}{)}^{\ensuremath{\beta}}$ with $\ensuremath{\beta}\ensuremath{\simeq}0.45$.

6,514 citations


"Stability of multiagent systems wit..." refers background or methods in this paper

  • ...Denote the direction of motion of particle by . The following model is studied in [ 11 ]:...

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  • ...In the physics literature, swarming models are often individual-based with each individual being represented by a particle moving at constant speed, its direction of motion being updated according to nearest neighbor coupling; see, for example, [ 11 ]....

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  • ...Example 4 (Swarming): Reference [ 11 ] proposes a simple model to investigate self-ordered motion in systems of particles with biologically motivated interaction....

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  • ...1 Within the context of swarming models [ 11 ], [14], agent could be a particle moving at constant speed in two-dimensional space and could represent its heading....

    [...]

  • ...The approach of the present paper applies to the linear swarming model of [14] as well as to the nonlinear model of [ 11 ] provided the initial orientation differences are sufficiently small....

    [...]

Journal ArticleDOI
TL;DR: A theoretical framework for design and analysis of distributed flocking algorithms, and shows that migration of flocks can be performed using a peer-to-peer network of agents, i.e., "flocks need no leaders."
Abstract: In this paper, we present a theoretical framework for design and analysis of distributed flocking algorithms. Two cases of flocking in free-space and presence of multiple obstacles are considered. We present three flocking algorithms: two for free-flocking and one for constrained flocking. A comprehensive analysis of the first two algorithms is provided. We demonstrate the first algorithm embodies all three rules of Reynolds. This is a formal approach to extraction of interaction rules that lead to the emergence of collective behavior. We show that the first algorithm generically leads to regular fragmentation, whereas the second and third algorithms both lead to flocking. A systematic method is provided for construction of cost functions (or collective potentials) for flocking. These collective potentials penalize deviation from a class of lattice-shape objects called /spl alpha/-lattices. We use a multi-species framework for construction of collective potentials that consist of flock-members, or /spl alpha/-agents, and virtual agents associated with /spl alpha/-agents called /spl beta/- and /spl gamma/-agents. We show that migration of flocks can be performed using a peer-to-peer network of agents, i.e., "flocks need no leaders." A "universal" definition of flocking for particle systems with similarities to Lyapunov stability is given. Several simulation results are provided that demonstrate performing 2-D and 3-D flocking, split/rejoin maneuver, and squeezing maneuver for hundreds of agents using the proposed algorithms.

4,693 citations


"Stability of multiagent systems wit..." refers background in this paper

  • ...In recent years, engineering applications such as formation control have increased the interest of engineers in swarming and collective motion patterns [12]–[26]....

    [...]

Journal ArticleDOI
TL;DR: A Nyquist criterion is proved that uses the eigenvalues of the graph Laplacian matrix to determine the effect of the communication topology on formation stability, and a method for decentralized information exchange between vehicles is proposed.
Abstract: We consider the problem of cooperation among a collection of vehicles performing a shared task using intervehicle communication to coordinate their actions. Tools from algebraic graph theory prove useful in modeling the communication network and relating its topology to formation stability. We prove a Nyquist criterion that uses the eigenvalues of the graph Laplacian matrix to determine the effect of the communication topology on formation stability. We also propose a method for decentralized information exchange between vehicles. This approach realizes a dynamical system that supplies each vehicle with a common reference to be used for cooperative motion. We prove a separation principle that decomposes formation stability into two components: Stability of this is achieved information flow for the given graph and stability of an individual vehicle for the given controller. The information flow can thus be rendered highly robust to changes in the graph, enabling tight formation control despite limitations in intervehicle communication capability.

4,377 citations


"Stability of multiagent systems wit..." refers background in this paper

  • ...Other studies that consider the connection between communication topology and system stability such as [14], [27]–[29], [31], [34], and [35] typically rely on algebraic graph theory, relating the graph topology with the algebraic structure of associated graph matrices....

    [...]

  • ...(Leaderless coordination is also considered, for example, in [34]–[38])....

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