List of English Publication

@article{nokey,

title = {How Does a Swarm Exhibit Emergent Behavior Through Synchronization?},

author = {Hyungbo Shim},

url = {https://icros.org/publication/sub03_04.asp?sub_param=4},

doi = {https://doi.org/10.5302/J.ICROS.2024.24.0039},

issn = {1976-5622},

year  = {2024},

date = {2024-04-01},

urldate = {2024-04-01},

journal = {Journal of Institute of Control, Robotics and Systems},

volume = {30},

issue = {4},

pages = {352},

abstract = {A swarm of individuals often exhibits behaviors that are not possible for each individual. This phenomenon is called emergence, and this paper mathematically demonstrates that new dynamics can arise in swarm behavior that cannot be explained by the dynamics of individuals. In particular, we argue that emergence occurs when heterogeneity is coupled with synchronization.

These two concepts may seem conflicting, as heterogeneity is the tendency to differ whereas synchronization is the tendency toward sameness. However, we show that emergent behavior arises from the interplay between the two.},

keywords = {Blended dynamics, Multi-agent systems, Synchronization},

pubstate = {published},

tppubtype = {article}

}

@article{Discrete-timeheterogeneousmulti-agentsystemMulti-stepcouplingBlendeddynamics,

title = {A design method of distributed algorithms via discrete-time blended dynamics theorem},

author = {Jeong Woo Kim and Jin Gyu Lee and Donggil Lee and Hyungbo Shim},

editor = {Automatica},

doi = {https://doi.org/10.1016/j.automatica.2023.111371},

issn = {0005-1098},

year  = {2024},

date = {2024-01-01},

urldate = {2024-01-01},

booktitle = {Automatica},

journal = {Automatica},

volume = {159},

pages = {111371},

abstract = {We develop a discrete-time version of the blended dynamics theorem for the use of designing distributed computation algorithms. The blended dynamics theorem enables to predict the behavior of heterogeneous multi-agent systems. Therefore, once we get a blended dynamics for a particular computational task, design idea of node dynamics for individual heterogeneous agents can easily occur. In the continuous-time case, prediction by blended dynamics was enabled by high coupling gain among neighboring agents. In the discrete-time case, we propose an equivalent action, which we call multi-step coupling in this paper. Compared to the continuous-time case, the blended dynamics can have more variety depending on the coupling matrix. This benefit is demonstrated with three applications; distributed estimation of network size, distributed computation of the PageRank, and distributed computation of the degree sequence of a graph, which correspond to the coupling by doubly-stochastic, column-stochastic, and row-stochastic matrices, respectively.},

key = {Discrete-time heterogeneous multi-agent systemMulti-step couplingBlended dynamics},

keywords = {Blended dynamics, Discrete-time blended dynamics, Discrete-time heterogeneous multi-agent system, Multi-step coupling},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Edge-wise funnel output synchronization of heterogeneous agents with relative degree one},

author = {Jin Gyu Lee and Thomas Berger and Stephan Trenn and Hyungbo Shim},

url = {https://www.sciencedirect.com/science/article/pii/S0005109823003655},

doi = {https://doi.org/10.1016/j.automatica.2023.111204},

issn = {0005-1098},

year  = {2023},

date = {2023-10-01},

urldate = {2023-10-01},

journal = {Automatica},

volume = {156},

pages = {111204},

abstract = {When a group of heterogeneous node dynamics are diffusively coupled with a high coupling gain, the

group exhibits a collective emergent behavior which is governed by a simple algebraic average of the

node dynamics called the blended dynamics. This finding has been utilized for designing heterogeneous

multi-agent systems by building the desired blended dynamics first and then splitting it into the node

dynamics. However, to compute the magnitude of the coupling gain, each agent needs to know global

information such as the number of participating nodes, the graph structure, and so on, which prevents

a fully decentralized design of the node dynamics in conjunction with the coupling laws. To resolve this

issue, the idea of funnel control, which is a method for adaptive gain selection, can be exploited for a

node-wise coupling, but the price to pay is that the collective emergent behavior is no longer governed

by a simple average of the node dynamics. Our analysis reveals that this drawback can be avoided by an

edge-wise design premise, which is the idea that we present in this paper. After all, we gain benefits

such as a fully decentralized design without global information, collective emergent behavior being

governed by the blended dynamics, and the plug-and-play operation based on edge-wise handshaking

between two nodes},

keywords = {Blended dynamics, Funnel control, Heterogeneous multi-agents, output synchronization},

pubstate = {published},

tppubtype = {article}

}

@article{nokeyp,

title = {Distributed Resilient Observer: Blended Dynamics Theory Meets ℓ1-Minimization Approach},

author = {Donggil Lee and Junsoo Kim and Hyungbo Shim},

url = {https://ieeexplore.ieee.org/document/10147254/},

doi = {10.1109/LCSYS.2023.3284592},

issn = {2475-1456},

year  = {2023},

date = {2023-06-09},

urldate = {2023-06-09},

journal = {IEEE Control Systems Letters},

volume = {7},

pages = {2083 - 2088},

abstract = {This paper presents a distributed resilient observer for continuous-time linear time-invariant plants that remains functional even under sensor attacks. The proposed method aims to determine the estimation outcome that matches the majority of sensor measurements, which is formulated as an ℓ1-minimization problem considering all the observable components of each sensor measurement. A distributed observer based on the blended dynamics theory is then proposed to solve the ℓ1-minimization problem in a distributed manner. As a result, the distributed resilient estimation is enabled for a broader class of systems compared to previous works. The design procedure is constructive with parameters obtained from a specified condition that is equivalent to the well-known null-space property.},

keywords = {Blended dynamics, Blended Dynamics Approach, Distributed state estimation, Resilient state estimation},

pubstate = {published},

tppubtype = {article}

}

@article{Lee20,

title = {A Tool for Analysis and Synthesis of Heterogeneous Multi-agent Systems under Rank-deficient Coupling},

author = {Jin Gyu Lee/ Hyungbo Shim},

doi = {https://doi.org/10.1016/j.automatica.2020.108952},

issn = {0005-1098},

year  = {2020},

date = {2020-07-01},

urldate = {2020-07-01},

journal = {Automatica},

volume = {117},

pages = {108952},

abstract = {The behavior of heterogeneous multi-agent systems is studied when the coupling matrices are possibly all different and/or singular, that is, its rank is less than the system dimension. Rank-deficient coupling allows exchange of limited state information, which is suitable for the study of multi-agent systems under output coupling. We present a coordinate change that transforms the heterogeneous multi-agent system into a singularly perturbed form. The slow dynamics is still a reduced-order multi-agent system consisting of a weighted average of the vector fields of all agents, and some sub-dynamics of agents. The weighted average is an emergent dynamics, which we call a blended dynamics. By analyzing or synthesizing the blended dynamics, one can predict or design the behavior of a heterogeneous multi-agent system when the coupling gain is sufficiently large. For this result, stability of the blended dynamics is required. Since stability of the individual agent is not asked, the stability of the blended dynamics is the outcome of trading off the stability among the agents. It can be seen that, under the stability of the blended dynamics, the initial conditions of the individual agents are forgotten as time goes on, and thus, the behavior of the synthesized multi-agent system is initialization-free and is suitable for plug-and-play operation. As a showcase, we apply the proposed tool to four application problems; distributed state estimation for linear systems, practical synchronization of heterogeneous van der Pol oscillators, estimation of the number of nodes in a network, and a problem of distributed optimization.},

keywords = {Blended dynamics, Heterogeneous multi-agents, Singular perturbation, Synchronization},

pubstate = {published},

tppubtype = {article}

}

@article{Lee20b,

title = {Fully distributed resilient state estimation based on distributed median solver},

author = {Jin Gyu Lee and Junsoo Kim and Hyungbo Shim},

doi = {https://doi.org/10.1109/TAC.2020.2989275},

issn = {0018-9286},

year  = {2020},

date = {2020-04-01},

journal = {IEEE Transactions on Automatic Control},

volume = {65},

number = {9},

pages = {3935-3942},

abstract = {In this article, we present a scheme of fully distributed resilient state estimation for linear dynamical systems under sensor attacks. The proposed state observer consists of a network of local observers, where each of them utilizes local measurements and information transmitted from the neighbors. As a fully distributed scheme, it does not necessarily collect a majority of sensing data for the sake of attack identification, whereas the compromised sensors are eventually identified by the distributed network and excluded from the observers. For this, the overall network (not the individual local observer) is assumed to have redundant sensors and assumed to be connected. The proposed scheme is based on a novel design of a distributed median solver, which approximately recovers the median value of local estimates.},

keywords = {Analytical redundancy, Attack detection, Attack resilience, Blended dynamics, Cyber-physical systems, Heterogeneous multi-agents, Resilient state estimation, Strong coupling},

pubstate = {published},

tppubtype = {article}

}

@article{LeeShim19,

title = {Distributed Algorithm for Economic Dispatch Problem With Separable Losses},

author = {Seungjoon Lee and Hyungbo Shim},

doi = {10.1109/LCSYS.2019.2916250},

year  = {2019},

date = {2019-06-22},

journal = {IEEE Control Systems Letters},

volume = {3},

number = {3},

pages = {685-690},

keywords = {Blended dynamics, Distributed optimization},

pubstate = {published},

tppubtype = {article}

}

@article{YunShimAhn19,

title = {Initialization-free Privacy-guaranteed Distributed Algorithm for Economic Dispatch Problem},

author = {Hyeonjun Yun and Hyungbo Shim and Hyo-Sung Ahn},

url = {https://post.cdsl.kr/archives/615

https://arxiv.org/abs/1801.01658},

doi = {10.1016/j.automatica.2018.12.033},

year  = {2019},

date = {2019-04-01},

journal = {Automatica},

volume = {102},

pages = {86-93},

abstract = {This paper considers the economic dispatch problem for a network of power generators and customers. In particular, our aim is to minimize the total generation cost under the power supply-demand balance and the individual generation capacity constraints. This problem is solved in a distributed manner, i.e., a dual gradient-based continuous-time distributed algorithm is proposed in which only a single dual variable is communicated with the neighbors and no private information of the node is disclosed. The proposed algorithm is simple and no specific initialization is necessary, and this in turn allows on-line change of network structure, demand, generation constraints, and even the participating nodes. The algorithm also exhibits a special behavior when the problem becomes infeasible so that each node can detect over-demand or under-demand situation of the power network. Simulation results on IEEE 118 bus system confirm robustness against variations in power grids.},

keywords = {Blended dynamics, Synchronization},

pubstate = {published},

tppubtype = {article}

}

@article{KimYangShimKimSeo16,

title = {Robustness of Synchronization of Heterogeneous Agents by Strong Coupling and a Large Number of Agents},

author = {Jaeyong Kim and Jongwook Yang and Hyungbo Shim and Jung-Su Kim and Jin Heon Seo},

doi = {10.1109/TAC.2015.2498138},

year  = {2016},

date = {2016-10-01},

journal = {IEEE Transactions on Automatic Control},

volume = {61},

number = {10},

pages = {3096-3102},

abstract = {This technical note studies robustness of synchronization against heterogeneity of multi-agent systems. Here, heterogeneity also includes uncertainties and external disturbances in each agent. In order to effectively deal with the heterogeneous agents, we introduce the concept of the averaged dynamics which is the average of all agents’ dynamics, and then claim that two sources enhance the robustness of synchronized behavior against heterogeneity of agents’ dynamics. First, in spite of the heterogeneity of agents’ dynamics, we show that strong coupling among agents makes the trajectories of all agents arbitrarily close to the averaged dynamics. Second, in the averaged dynamics, the effect of variations in each agent gets smaller as the number of agents increases. Simulation results confirm the claim that a large number of agents with strong couplings have robust synchronization.},

keywords = {Blended dynamics, Heterogeneity, Multi-agent system, Synchronization},

pubstate = {published},

tppubtype = {article}

}