Robust Distributed Sub-Optimal Coordination of Linear Agents with Uncertain Input Nonlinearities
Pith reviewed 2026-05-10 04:23 UTC · model grok-4.3
The pith
A distributed control protocol steers linear agents with uncertain input nonlinearities to a neighborhood of the global optimizer by unifying nonlinearities and gradients through sector conditions.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
We study robust distributed sub-optimal coordination of linear agents subject to input nonlinearities. We formulate a bounded distributed sub-optimal coordination problem in which each agent converges to a neighborhood of the optimizer of a global optimization problem defined over a communication network. We propose a novel control protocol and analyze convergence by employing a robust control approach in which both the input nonlinearities and the gradients of the objective functions are treated in a unified manner via sector conditions. We derive sufficient conditions for the solvability of the considered problem and characterize them in terms of matrix inequalities.
What carries the argument
A novel distributed control protocol whose stability is certified by a robust-control analysis that treats input nonlinearities and objective gradients uniformly through sector conditions, yielding matrix-inequality solvability criteria.
If this is right
- The matrix inequalities supply a practical test that certifies whether a given network and set of sector bounds admit sub-optimal coordination.
- Convergence occurs to a neighborhood whose size is governed by the sector bounds rather than to the exact optimizer.
- The same sector-based treatment covers both actuator nonlinearities and the shape of the cost functions.
- The protocol remains distributed, using only neighbor information over the given communication graph.
Where Pith is reading between the lines
- The sector-condition approach could be reused for other bounded uncertainties, such as time delays or switching topologies, provided they also admit sector representations.
- The framework suggests a route to sub-optimal coordination for agents whose dynamics are themselves nonlinear, if those dynamics can be absorbed into enlarged sector bounds.
- Numerical verification of the matrix inequalities on realistic network sizes would indicate how conservative the sufficient conditions are in practice.
Load-bearing premise
Both the uncertain input nonlinearities and the gradients of the objective functions obey sector bounds that allow them to be handled together in a single robust-control framework.
What would settle it
A simulation or analytic counterexample in which the sector bounds hold and the matrix inequalities are satisfied yet the agents do not enter a neighborhood of the optimizer, or a case where the bounds are violated and the protocol still succeeds.
Figures
read the original abstract
In this paper, we study robust distributed sub-optimal coordination of linear agents subject to input nonlinearities. Inspired by the robust agreement literature, we formulate a bounded distributed sub-optimal coordination problem, in which each agent converges to a neighborhood of the optimizer of a global optimization problem defined over a communication network. We propose a novel control protocol, and analyze convergence by employing a robust control approach, in which both the input nonlinearities and the gradients of the objective functions are treated in a unified manner via sector conditions. In particular, we derive sufficient conditions for the solvability of the considered problem and characterize them in terms of matrix inequalities. The effectiveness of the proposed method is demonstrated through a numerical simulation.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper studies robust distributed sub-optimal coordination for linear agents subject to uncertain input nonlinearities. It formulates a bounded coordination problem where agents converge to a neighborhood of the global optimizer of a networked sum of local costs. A novel distributed protocol is proposed and convergence is analyzed via a robust-control Lyapunov approach that treats both the input nonlinearities and the cost gradients as sector-bounded uncertainties in a unified manner. Sufficient conditions for solvability are derived and expressed as linear matrix inequalities; effectiveness is illustrated by a numerical simulation.
Significance. If the LMI conditions are feasible, the unified sector-bound treatment provides a systematic LMI-based design method for distributed approximate optimization under actuator nonlinearities, extending ideas from robust agreement to optimization settings. This could be useful for networked systems with uncertain actuators. The approach is technically standard but the unification of nonlinearity and gradient sectors is a modest positive contribution; practical impact is limited by the requirement that sector parameters be known.
major comments (2)
- [Problem statement and main LMI conditions (likely §3–4)] Problem statement and main LMI conditions (likely §3–4): The sector bounds on the uncertain input nonlinearities are taken as known a priori and appear directly as parameters in the derived matrix inequalities. No procedure, over-bound, or data-driven method is supplied for obtaining or conservatively estimating these bounds when the nonlinearity (e.g., saturation level, dead-zone width) is truly uncertain. Because the feasibility of the LMIs and the size of the convergence neighborhood depend explicitly on these parameters, the sufficient conditions cannot be instantiated for real systems without an additional modeling step that the manuscript does not address.
- [Convergence analysis] Convergence analysis: The neighborhood radius to which agents converge is characterized in terms of the sector parameters and the sub-optimality tolerance, but the manuscript does not provide an explicit scaling law or sensitivity result showing how the radius grows with increasing uncertainty in the input nonlinearity. Adding such a remark or corollary after the main theorem would strengthen the claim that the method is robust.
minor comments (2)
- [Numerical simulation] The numerical example would be more informative if the specific LMI solver, feasibility margin, and condition number of the solved matrices were reported, allowing readers to assess numerical reliability.
- [Preliminaries] Notation for the communication graph (Laplacian, adjacency matrix) should be introduced once in the preliminaries and used consistently thereafter.
Simulated Author's Rebuttal
We thank the referee for the constructive comments, which help clarify the practical aspects of our robust control design. We address each major comment below and will revise the manuscript accordingly to improve its completeness.
read point-by-point responses
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Referee: Problem statement and main LMI conditions (likely §3–4): The sector bounds on the uncertain input nonlinearities are taken as known a priori and appear directly as parameters in the derived matrix inequalities. No procedure, over-bound, or data-driven method is supplied for obtaining or conservatively estimating these bounds when the nonlinearity (e.g., saturation level, dead-zone width) is truly uncertain. Because the feasibility of the LMIs and the size of the convergence neighborhood depend explicitly on these parameters, the sufficient conditions cannot be instantiated for real systems without an additional modeling step that the manuscript does not address.
Authors: We agree that the sector bounds are assumed known a priori, as is standard in the sector-bounded uncertainty framework used throughout the robust control literature. For common actuator nonlinearities such as saturation or dead-zones, these parameters are typically available from manufacturer specifications or can be conservatively over-estimated via simple experiments. To address the concern, we will insert a short remark in the problem statement section explaining how to select such bounds in practice, thereby providing the missing modeling guidance while preserving the LMI-based synthesis as the main contribution. revision: yes
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Referee: Convergence analysis: The neighborhood radius to which agents converge is characterized in terms of the sector parameters and the sub-optimality tolerance, but the manuscript does not provide an explicit scaling law or sensitivity result showing how the radius grows with increasing uncertainty in the input nonlinearity. Adding such a remark or corollary after the main theorem would strengthen the claim that the method is robust.
Authors: We concur that an explicit sensitivity result would better highlight the robustness properties. We will add a corollary right after the main theorem that derives an explicit upper bound on the convergence neighborhood radius and shows its linear scaling with the sector parameters of the input nonlinearities. This addition will make the dependence on uncertainty transparent without requiring changes to the proof technique. revision: yes
Circularity Check
No circularity: standard sector-bound robust control applied to new coordination problem
full rationale
The derivation begins from a standard problem formulation of distributed sub-optimal coordination, proposes a protocol, and applies existing robust-control sector conditions simultaneously to input nonlinearities and cost gradients to obtain LMI feasibility conditions. No equation reduces to a prior fitted parameter or self-definition; the matrix inequalities are obtained via standard Lyapunov analysis or S-procedure on the closed-loop dynamics. No self-citations are invoked as load-bearing uniqueness theorems, and the sector bounds are treated as given modeling assumptions rather than derived outputs. The chain is therefore self-contained against external robust-control benchmarks and does not collapse by construction.
Axiom & Free-Parameter Ledger
axioms (2)
- domain assumption Input nonlinearities and objective function gradients satisfy sector conditions.
- domain assumption The communication network is connected and permits distributed protocol implementation.
Reference graph
Works this paper leans on
-
[1]
T. Yang, X. Yi, J. Wu, Y. Yuan, D. Wu, Z. Meng, Y. Hong, H. Wang, Z. Lin, K. H. Johansson, A survey of distributed optimization, Annual Reviews in Control 47 (2019) 278–305
work page 2019
-
[2]
J. Wang, N. Elia, A control perspective for centralized and distributed convex optimization, in: Proceedings of the 50th Conference on Decision and Control and European Control Conference, 2011, pp. 3800–3805
work page 2011
-
[3]
G. Yu, Y. Shen, Event-triggered distributed optimisation for multi-agent systems with transmission delay , IET Control Theory & Applications 13 (2019) 2188–2196
work page 2019
-
[4]
Z. Deng, X. Wang, Y. Hong, Distributed optimisation design with triggers for disturbed continuous-time multi-agent systems, IET Control Theory & Applications 11 (2017) 282–290
work page 2017
-
[5]
C. Xian, Y. Zhao, G. Wen, G. Chen, Robust event-triggered distributed optimal coordination of heterogeneous systems over directed networks, IEEE Transactions on Automatic Control 69 (2024) 4522–4537
work page 2024
-
[6]
C. Xian, Y. Liu, Y. Zhao, G. Chen, Distributed optimal coordination of multiple heterogeneous linear systems over unbalanced directed communication networks, Systems and Control Letters 183 (2024) 105967
work page 2024
-
[7]
L. An, G. H. Yang, Distributed optimal coordination for heterogeneous linear multiagent systems, IEEE Transactions on Automatic Control 67 (2022) 6850–6857
work page 2022
-
[8]
Z. Li, Z. Wu, Z. Li, Z. Ding, Distributed optimal coordination for heterogeneous linear multiagent systems with event-triggered mechanisms, IEEE Transactions on Automatic Control 65 (2020) 1763–1770. T. Namba:Preprint Page 12 of 13 Robust Distributed Sub-Optimal Coordination of Linear Agents with Uncertain Input Nonlinearities
work page 2020
-
[9]
Y. Yu, X. Li, L. Li, L. Xie, Distributed online optimization for heterogeneous linear multi-agent systems with coupled constraints, Automatica 159 (2024) 111407
work page 2024
-
[10]
Z. Deng, J. Luo, Fully distributed algorithms for constrained nonsmooth optimization problems of general linear multiagent systems and their application, IEEE Transactions on Automatic Control 69 (2024) 1377–1384
work page 2024
-
[11]
L. Li, Y. Yu, X. Li, L. Xie, Exponential convergence of distributed optimization for heterogeneous linear multi-agent systems over unbalanced digraphs, Automatica 141 (2022) 110259
work page 2022
- [12]
- [13]
-
[14]
A. Wang, X. Liao, T. Dong, Event-triggered gradient-based distributed optimisation for multi-agent systems with state consensus constraint, IET Control Theory & Applications 12 (2018) 1515–1519
work page 2018
- [15]
- [16]
-
[17]
A. R. Romano, L. Pavel, Game-theoretic steady-state control, in: Proceedings of the 61st IEEE Conference on Decision and Control (CDC’22), 2022, pp. 2493–2499
work page 2022
-
[18]
A. R. Romano, L. Pavel, Controller design for game theoretic steady-state control: An lmi approach, in: IFAC PapersOnLine, 2023, pp. 5101–5106
work page 2023
-
[19]
H. L. Trentelman, K. Takaba, N. Monshizadeh, Robust synchronization of uncertain linear multi-agent systems, IEEE Transactions on Automatic Control 58 (2013) 1511–1523
work page 2013
-
[20]
D. H. Nguyen, T. Narikiyo, M. Kawanishi, Robust consensus analysis and design under relative state constraints or uncertainties, IEEE Transactions on Automatic Control 63 (2018) 1694–1700
work page 2018
-
[21]
K. Takaba, Local synchronization of linear multi-agent systems subject to input saturation, SICE Journal of Control, Measurement, and System Integration 8 (2015) 334–340
work page 2015
-
[22]
K. Takaba, Synchronization of linear agents with sector-bounded input nonlinearities, in: Proceedings of the 15th International Conference on Control, Automation and Systems (ICCAS2015), 2015, pp. 1–6
work page 2015
- [23]
-
[24]
H. Yu, T. Chen, A new Zeno-free event-triggered scheme for robust distributed optimal coordination, Automatica 129 (2021) 109639
work page 2021
-
[25]
Z. Zhao, J. Ding, J.-X. Zhang, T. Yang, Y. Shi, Fully distributed sub-optimal coordination for nonlinear multi-agent systems, IEEE Transactions on Automation Science and Engineering 23 (2026) 5212–5224
work page 2026
-
[26]
T. Namba, Dynamics-aware distributed optimization over a network of input-saturated linear agents, IFAC-PapersOnLine 59 (2025) 55–60. 19th IFAC Workshop on Control Applications of Optimisation CAO 2025
work page 2025
- [27]
-
[28]
W. Han, Z. Wang, Y. Shen,ℎ ∞ consensus of directed Lur’e networks with incremental nonlinearities, Asian Journal of Control 22 (2020) 536–546
work page 2020
-
[29]
D. P. Bertsekas, Convex Optimization Theory , Athena Scientific, 2009
work page 2009
-
[30]
Bullo, Lectures on Network Systems, 1.7 ed., Kindle Direct Publishing, 2024
F. Bullo, Lectures on Network Systems, 1.7 ed., Kindle Direct Publishing, 2024. URL:https://fbullo.github.io/lns
work page 2024
- [31]
-
[32]
Khalil, Nonlinear Systems, third ed., Prentice-Hall, Upper Saddle River, NJ, USA, 2002
H. Khalil, Nonlinear Systems, third ed., Prentice-Hall, Upper Saddle River, NJ, USA, 2002
work page 2002
-
[33]
Q. T. Dinh, W. Michiels, M. Diehl, An inner convex approximation algorithm for BMI optimization and applications in control,
- [34]
-
[35]
S. Boyd, L. El Ghaoui, E. Feron, V. Balakrishnan, Linear matrix inequalities in system and control theory , SIAM, 1994
work page 1994
-
[36]
J. Lofberg, YALMIP: A toolbox for modeling and optimization in MATLAB, in: 2004 IEEE International conference on robotics and automation, IEEE, 2004, pp. 284–289
work page 2004
-
[37]
M. ApS, MOSEK optimization toolbox for MATLAB, User’s Guide and Reference Manual, Release 11.1.10 (2026)
work page 2026
-
[38]
Z. Li, Z. Duan, F. L. Lewis, Distributed robust consensus control of multi-agent systems with heterogeneous matching uncertainties, Automatica 50 (2014) 883–889. T. Namba:Preprint Page 13 of 13
work page 2014
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