Scalable Verification of Neural Control Barrier Functions Using Linear Bound Propagation
Pith reviewed 2026-05-17 23:32 UTC · model grok-4.3
The pith
Linear bound propagation on network gradients yields scalable checks for neural control barrier functions.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
We present a novel framework for verifying neural CBFs based on piecewise linear upper and lower bounds on the conditions required for a neural network to be a CBF. Our approach is rooted in linear bound propagation for neural networks, which we extend to compute bounds on the gradients of the network. Combined with McCormick relaxation, we derive linear upper and lower bounds on the CBF conditions, thereby eliminating the need for computationally expensive verification procedures. Our approach applies to arbitrary control-affine systems and a broad range of nonlinear activation functions. To reduce conservatism, we develop a parallelizable refinement strategy that adaptively refines the
What carries the argument
Linear bound propagation extended to network gradients, combined with McCormick envelopes to produce linear bounds on the CBF Lie-derivative conditions.
Load-bearing premise
The upper and lower bounds obtained from gradient propagation and McCormick relaxations remain tight enough after adaptive refinement to certify the CBF conditions over the full state space without prohibitive conservatism.
What would settle it
Run the method on a neural CBF known to be valid by an exact but slower verifier; if it reports invalidity, or conversely certifies an invalid network, the claim fails.
Figures
read the original abstract
Control barrier functions (CBFs) are a popular tool for safety certification of nonlinear dynamical control systems. Recently, CBFs represented as neural networks have shown great promise due to their expressiveness and applicability to a broad class of dynamics and safety constraints. However, verifying that a trained neural network is indeed a valid CBF is a computational bottleneck that limits the size of the networks that can be used. To overcome this limitation, we present a novel framework for verifying neural CBFs based on piecewise linear upper and lower bounds on the conditions required for a neural network to be a CBF. Our approach is rooted in linear bound propagation (LBP) for neural networks, which we extend to compute bounds on the gradients of the network. Combined with McCormick relaxation, we derive linear upper and lower bounds on the CBF conditions, thereby eliminating the need for computationally expensive verification procedures. Our approach applies to arbitrary control-affine systems and a broad range of nonlinear activation functions. To reduce conservatism, we develop a parallelizable refinement strategy that adaptively refines the regions over which these bounds are computed. Our approach scales to larger neural networks than state-of-the-art verification procedures for CBFs, as demonstrated by our numerical experiments.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper introduces a verification framework for neural network control barrier functions (CBFs) on control-affine systems. It extends linear bound propagation (LBP) to obtain linear upper/lower bounds on both the network output and its gradient, then applies McCormick relaxations to the bilinear terms appearing in the Lie-derivative CBF condition. An adaptive, parallelizable partitioning scheme is used to tighten the bounds until the certified lower bound on sup_u (L_f h + L_g h u) + α(h) is non-negative over the entire domain. The central claim is that this procedure scales to larger networks than existing SMT-based or optimization-based CBF verifiers, as demonstrated by numerical experiments.
Significance. If the tightness and scalability claims hold, the method would remove a major computational obstacle to deploying expressive neural CBFs on higher-dimensional or more complex control-affine plants. The combination of established LBP primitives with McCormick envelopes and adaptive refinement is a natural and potentially practical advance over purely symbolic or SMT approaches. The numerical experiments provide initial evidence that the approach can handle networks larger than those verified by prior art.
major comments (3)
- [§4.2] §4.2 and Algorithm 1: the adaptive refinement procedure is described at a high level, but no explicit bound is given on the worst-case number of regions or the depth of the refinement tree as a function of state dimension or network width. Without such an analysis or a worst-case example, it is difficult to assess whether the claimed scalability advantage over SMT solvers persists when the McCormick envelopes or gradient bounds become loose.
- [§3.3] §3.3, Eq. (12)–(15): the McCormick relaxation is applied to the product L_g h(x)·u. The manuscript should state the precise interval bounds used for u and for the gradient components, and should quantify how the relaxation gap grows with the width of those intervals. If the intervals are not tightened during refinement, the certified lower bound may remain negative even when a valid CBF exists.
- [Experiments] Experiments section, Table 2: the reported verification times and network sizes are compared only against a single baseline (SMT-based verifier). A more informative comparison would include at least one additional relaxation-based or abstraction-refinement method to isolate the contribution of the LBP+McCormick combination.
minor comments (2)
- [§2] Notation for the control-affine dynamics f(x) and g(x) is introduced without an explicit statement of the assumed regularity (e.g., Lipschitz constants or boundedness of g).
- [Figure 3] Figure 3 caption should clarify whether the plotted lower bounds are the final certified values after refinement or intermediate values.
Simulated Author's Rebuttal
We thank the referee for their constructive and detailed comments on our manuscript. We have addressed each major comment below, making revisions where appropriate to improve clarity and completeness while maintaining the core contributions.
read point-by-point responses
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Referee: [§4.2] §4.2 and Algorithm 1: the adaptive refinement procedure is described at a high level, but no explicit bound is given on the worst-case number of regions or the depth of the refinement tree as a function of state dimension or network width. Without such an analysis or a worst-case example, it is difficult to assess whether the claimed scalability advantage over SMT solvers persists when the McCormick envelopes or gradient bounds become loose.
Authors: We agree that a formal worst-case analysis of the refinement tree would strengthen the presentation. Deriving a tight, general bound is challenging because the number of partitions depends on the initial bound tightness, the specific dynamics, and the network weights rather than solely on dimension or width. In the worst case the tree depth can grow exponentially with state dimension, similar to other adaptive abstraction-refinement schemes. We have added a new paragraph to Section 4.2 that explicitly states this limitation, provides a simple worst-case example on a one-dimensional system, and explains why the parallelizable adaptive stopping criterion still yields practical scalability on the networks tested in the experiments. revision: partial
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Referee: [§3.3] §3.3, Eq. (12)–(15): the McCormick relaxation is applied to the product L_g h(x)·u. The manuscript should state the precise interval bounds used for u and for the gradient components, and should quantify how the relaxation gap grows with the width of those intervals. If the intervals are not tightened during refinement, the certified lower bound may remain negative even when a valid CBF exists.
Authors: We thank the referee for highlighting this point. In the revised Section 3.3 we now explicitly state that the control set U is taken to be a compact hyper-rectangle (e.g., U = [-1,1]^m in all reported experiments) and that the interval bounds on each component of L_g h(x) are those returned by the extended linear bound propagation procedure over the current partition region. We have also added a short derivation showing that the McCormick relaxation gap for the bilinear term is bounded by (1/4)·w_a·w_b, where w_a and w_b are the widths of the intervals for L_g h and u, respectively. Because refinement partitions the state domain, the LBP-computed gradient bounds tighten monotonically, thereby reducing the gap; this dependence is now quantified in the text. revision: yes
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Referee: Experiments section, Table 2: the reported verification times and network sizes are compared only against a single baseline (SMT-based verifier). A more informative comparison would include at least one additional relaxation-based or abstraction-refinement method to isolate the contribution of the LBP+McCormick combination.
Authors: We acknowledge that a single baseline limits the ability to isolate the benefit of the LBP+McCormick combination. In the revised experiments section we have added two further baselines: (i) a pure interval-arithmetic + McCormick verifier without linear bound propagation on gradients, and (ii) a uniform-grid abstraction-refinement method. The updated Table 2 now reports verification times and success rates for all three methods on the same network suite, thereby highlighting the contribution of the gradient bounds obtained via LBP. revision: yes
Circularity Check
No significant circularity; derivation uses established external primitives
full rationale
The paper's core derivation extends linear bound propagation (LBP) to neural network gradients and combines it with McCormick envelopes on the bilinear terms arising in the Lie derivative of the neural CBF. These primitives are drawn from the independent literature on neural verification and convex relaxations rather than being defined in terms of the target CBF conditions or fitted to them. The adaptive partitioning step is a standard refinement heuristic to tighten bounds and does not presuppose the final certified result. No equation reduces by construction to a fitted parameter or to a self-citation whose validity depends on the present work; the method remains self-contained against external benchmarks for bound propagation.
Axiom & Free-Parameter Ledger
axioms (2)
- domain assumption The dynamical system is control-affine
- domain assumption The activation functions belong to a broad but fixed class for which LBP bounds exist
Forward citations
Cited by 1 Pith paper
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Efficient Verification of Neural Control Barrier Functions with Smooth Nonlinear Activations
LightCROWN computes tighter Jacobian bounds for neural networks with smooth nonlinear activations by exploiting their analytical properties, raising verification success rates for neural control barrier functions up t...
Reference graph
Works this paper leans on
-
[1]
Counterexample guided inductive synthesis modulo theories
Alessandro Abate, Cristina David, Pascal Kesseli, Daniel Kroening, and Elizabeth Polgreen. Counterexample guided inductive synthesis modulo theories. In CAV (1) , volume 10981 of Lecture Notes in Computer Science, pages 270--288. Springer, 2018. doi:10.1007/978-3-319-96145-3_15
-
[2]
Alessandro Abate, Daniele Ahmed, Alec Edwards, Mirco Giacobbe, and Andrea Peruffo. FOSSIL: a software tool for the formal synthesis of L yapunov functions and barrier certificates using neural networks. In HSCC , pages 24:1--24:11. ACM , 2021 a . doi:10.1145/3447928.3456646
-
[3]
Formal synthesis of lyapunov neural networks
Alessandro Abate, Daniele Ahmed, Mirco Giacobbe, and Andrea Peruffo. Formal synthesis of lyapunov neural networks. IEEE Control. Syst. Lett. , 5 0 (3): 0 773--778, 2021 b . doi:10.1109/LCSYS.2020.3005328
-
[4]
Ayush Agrawal and Koushil Sreenath. Discrete control barrier functions for safety-critical control of discrete systems with application to bipedal robot navigation. In Robotics: Science and Systems, 2017. doi:10.15607/RSS.2017.XIII.073
-
[5]
Aaron D. Ames, Jessy W. Grizzle, and Paulo Tabuada. Control barrier function based quadratic programs with application to adaptive cruise control. In CDC , pages 6271--6278. IEEE , 2014. doi:10.1109/CDC.2014.7040372
-
[6]
Aaron D. Ames, Xiangru Xu, Jessy W. Grizzle, and Paulo Tabuada. Control barrier function based quadratic programs for safety critical systems. IEEE Trans. Autom. Control. , 62 0 (8): 0 3861--3876, 2017. doi:10.1109/TAC.2016.2638961
-
[7]
Ames, Samuel Coogan, Magnus Egerstedt, Gennaro Notomista, Koushil Sreenath, and Paulo Tabuada
Aaron D. Ames, Samuel Coogan, Magnus Egerstedt, Gennaro Notomista, Koushil Sreenath, and Paulo Tabuada. Control barrier functions: Theory and applications. In ECC , pages 3420--3431. IEEE , 2019. doi:10.23919/ECC.2019.8796030
-
[8]
Policy verification in stochastic dynamical systems using logarithmic neural certificates
Thom Badings, Wietze Koops, Sebastian Junges, and Nils Jansen. Policy verification in stochastic dynamical systems using logarithmic neural certificates. In CAV (2) , volume 15932 of Lecture Notes in Computer Science, pages 349--375. Springer, 2025. doi:10.1007/978-3-031-98679-6_16
-
[9]
Barry, Anirudha Majumdar, and Russ Tedrake
Andrew J. Barry, Anirudha Majumdar, and Russ Tedrake. Safety verification of reactive controllers for UAV flight in cluttered environments using barrier certificates. In ICRA , pages 484--490. IEEE , 2012. doi:10.1109/ICRA.2012.6225351
-
[10]
Joseph Breeden and Dimitra Panagou. Robust control barrier functions under high relative degree and input constraints for satellite trajectories. Autom., 155: 0 111109, 2023. doi:10.1016/J.AUTOMATICA.2023.111109
-
[11]
In: 60th IEEE Conference on Decision and Control, pp
Andrew Clark. Verification and synthesis of control barrier functions. In CDC , pages 6105--6112. IEEE , 2021. doi:10.1109/CDC45484.2021.9683520
-
[12]
Clarke, Orna Grumberg, Somesh Jha, Yuan Lu, and Helmut Veith
Edmund M. Clarke, Orna Grumberg, Somesh Jha, Yuan Lu, and Helmut Veith. Counterexample-guided abstraction refinement for symbolic model checking. J. ACM , 50 0 (5): 0 752--794, 2003. doi:10.1145/876638.876643
-
[13]
Discrete differential geometry: An applied introduction
Keenan Crane. Discrete differential geometry: An applied introduction. Notices of the AMS, Communication, 1153, 2018
work page 2018
-
[14]
Charles Dawson, Sicun Gao, and Chuchu Fan. Safe control with learned certificates: A survey of neural lyapunov, barrier, and contraction methods for robotics and control. IEEE Trans. Robotics , 39 0 (3): 0 1749--1767, 2023. doi:10.1109/TRO.2022.3232542
-
[15]
Automatic abstraction refinement for timed automata
Henning Dierks, Sebastian Kupferschmid, and Kim Guldstrand Larsen. Automatic abstraction refinement for timed automata. In FORMATS , volume 4763 of Lecture Notes in Computer Science, pages 114--129. Springer, 2007. doi:10.1007/978-3-540-75454-1_10
-
[16]
Fossil 2.0: Formal certificate synthesis for the verification and control of dynamical models
Alec Edwards, Andrea Peruffo, and Alessandro Abate. Fossil 2.0: Formal certificate synthesis for the verification and control of dynamical models. In HSCC , pages 26:1--26:10. ACM , 2024. doi:10.1145/3641513.3651398
-
[17]
Francisco Eiras, Adel Bibi, Rudy Bunel, Krishnamurthy Dj Dvijotham, Philip Torr, and M. Pawan Kumar. Efficient error certification for physics-informed neural networks. In ICML . OpenReview.net, 2024
work page 2024
-
[18]
Sicun Gao, Soonho Kong, and Edmund M. Clarke. dreal: An SMT solver for nonlinear theories over the reals. In CADE , volume 7898 of Lecture Notes in Computer Science, pages 208--214. Springer, 2013. doi:10.1007/978-3-642-38574-2_14
-
[19]
Kai - Chieh Hsu, Haimin Hu, and Jaime F. Fisac. The safety filter: A unified view of safety-critical control in autonomous systems. Annu. Rev. Control. Robotics Auton. Syst., 7 0 (1), 2024. doi:10.1146/ANNUREV-CONTROL-071723-102940
-
[20]
Verification of neural control barrier functions with symbolic derivative bounds propagation
Hanjiang Hu, Yujie Yang, Tianhao Wei, and Changliu Liu. Verification of neural control barrier functions with symbolic derivative bounds propagation. In CoRL, volume 270 of Proceedings of Machine Learning Research, pages 1797--1814. PMLR , 2024
work page 2024
-
[21]
Parameter synthesis for markov models: covering the parameter space
Sebastian Junges, Erika \' A brah \' a m, Christian Hensel, Nils Jansen, Joost - Pieter Katoen, Tim Quatmann, and Matthias Volk. Parameter synthesis for markov models: covering the parameter space. Formal Methods Syst. Des., 62 0 (1): 0 181--259, 2024. doi:10.1007/S10703-023-00442-X
-
[22]
H. Kimura and S. Kobayashi. Stochastic real-valued reinforcement learning to solve a nonlinear control problem. In IEEE SMC'99 Conference Proceedings. 1999 IEEE International Conference on Systems, Man, and Cybernetics (Cat. No.99CH37028), volume 5, pages 510--515 vol.5, 1999. doi:10.1109/ICSMC.1999.815604
-
[23]
Abstraction of elementary hybrid systems by variable transformation
Jiang Liu, Naijun Zhan, Hengjun Zhao, and Liang Zou. Abstraction of elementary hybrid systems by variable transformation. In FM , volume 9109 of Lecture Notes in Computer Science, pages 360--377. Springer, 2015. doi:10.1007/978-3-319-19249-9_23
-
[24]
Frederik Baymler Mathiesen, Simeon C. Calvert, and Luca Laurenti. Safety certification for stochastic systems via neural barrier functions. IEEE Control. Syst. Lett. , 7: 0 973--978, 2023. doi:10.1109/LCSYS.2022.3229865
-
[25]
Certified neural approximations of nonlinear dynamics
Frederik Baymler Mathiesen, Nikolaus Vertovec, Francesco Fabiano, Luca Laurenti, and Alessandro Abate. Certified neural approximations of nonlinear dynamics. CoRR, abs/2505.15497, 2025. doi:10.48550/ARXIV.2505.15497
-
[26]
Garth P. McCormick. Computability of global solutions to factorable nonconvex programs: Part I - convex underestimating problems. Math. Program., 10 0 (1): 0 147--175, 1976. doi:10.1007/BF01580665
-
[27]
Automated and formal synthesis of neural barrier certificates for dynamical models
Andrea Peruffo, Daniele Ahmed, and Alessandro Abate. Automated and formal synthesis of neural barrier certificates for dynamical models. In TACAS (1) , volume 12651 of Lecture Notes in Computer Science, pages 370--388. Springer, 2021. doi:10.1007/978-3-030-72016-2_20
-
[28]
Barrier certificates for nonlinear model validation
Stephen Prajna. Barrier certificates for nonlinear model validation. Autom., 42 0 (1): 0 117--126, 2006. doi:10.1016/J.AUTOMATICA.2005.08.007
-
[29]
Synthesizing barrier certificates of neural network controlled continuous systems via approximations
Meng Sha, Xin Chen, Yuzhe Ji, Qingye Zhao, Zhengfeng Yang, Wang Lin, Enyi Tang, Qiguang Chen, and Xuandong Li. Synthesizing barrier certificates of neural network controlled continuous systems via approximations. In DAC , pages 631--636. IEEE , 2021. doi:10.1109/DAC18074.2021.9586327
-
[30]
Control barrier functions for mechanical systems: Theory and application to robotic grasping
Wenceslao Shaw - Cortez, Denny Oetomo, Chris Manzie, and Peter Choong. Control barrier functions for mechanical systems: Theory and application to robotic grasping. IEEE Trans. Control. Syst. Technol. , 29 0 (2): 0 530--545, 2021. doi:10.1109/TCST.2019.2952317
-
[31]
Neural network verification with branch-and-bound for general nonlinearities
Zhouxing Shi, Qirui Jin, Zico Kolter, Suman Jana, Cho - Jui Hsieh, and Huan Zhang. Neural network verification with branch-and-bound for general nonlinearities. In TACAS (1) , volume 15696 of Lecture Notes in Computer Science, pages 315--335. Springer, 2025. doi:10.1007/978-3-031-90643-5_17
-
[32]
Series of abstractions for hybrid automata
Ashish Tiwari and Gaurav Khanna. Series of abstractions for hybrid automata. In HSCC , volume 2289 of Lecture Notes in Computer Science, pages 465--478. Springer, 2002. doi:10.1007/3-540-45873-5_36
-
[33]
Kim P. Wabersich, Andrew J. Taylor, Jason J. Choi, Koushil Sreenath, Claire J. Tomlin, Aaron D. Ames, and Melanie N. Zeilinger. Data-driven safety filters: Hamilton-jacobi reachability, control barrier functions, and predictive methods for uncertain systems. IEEE Control Systems Magazine, 43 0 (5): 0 137--177, 2023. doi:10.1109/MCS.2023.3291885
-
[34]
Assessing Safety for Control Systems Using Sum -of- Squares Programming
Han Wang, Kostas Margellos, and Antonis Papachristodoulou. Assessing Safety for Control Systems Using Sum -of- Squares Programming . In Polynomial Optimization , Moments , and Applications , volume 206, pages 207--234. Springer Nature Switzerland, Cham, 2023. ISBN 978-3-031-38658-9 978-3-031-38659-6. doi:10.1007/978-3-031-38659-6_7
-
[35]
Robust explanation constraints for neural networks
Matthew Wicker, Juyeon Heo, Luca Costabello, and Adrian Weller. Robust explanation constraints for neural networks. In ICLR . OpenReview.net, 2023
work page 2023
-
[36]
High-order control barrier functions
Wei Xiao and Calin Belta. High-order control barrier functions. IEEE Trans. Autom. Control. , 67 0 (7): 0 3655--3662, 2022. doi:10.1109/TAC.2021.3105491
-
[37]
Darboux-type barrier certificates for safety verification of nonlinear hybrid systems
Xia Zeng, Wang Lin, Zhengfeng Yang, Xin Chen, and Lilei Wang. Darboux-type barrier certificates for safety verification of nonlinear hybrid systems. In EMSOFT , pages 11:1--11:10. ACM , 2016. doi:10.1145/2968478.2968484
-
[38]
Exact verification of relu neural control barrier functions
Hongchao Zhang, Junlin Wu, Yevgeniy Vorobeychik, and Andrew Clark. Exact verification of relu neural control barrier functions. In NeurIPS, 2023
work page 2023
-
[39]
Efficient neural network robustness certification with general activation functions
Huan Zhang, Tsui - Wei Weng, Pin - Yu Chen, Cho - Jui Hsieh, and Luca Daniel. Efficient neural network robustness certification with general activation functions. In NeurIPS, pages 4944--4953, 2018
work page 2018
-
[40]
Synthesizing barrier certificates using neural networks
Hengjun Zhao, Xia Zeng, Taolue Chen, and Zhiming Liu. Synthesizing barrier certificates using neural networks. In HSCC , pages 25:1--25:11. ACM , 2020. doi:10.1145/3365365.3382222
-
[41]
Verifying neural network controlled systems using neural networks
Qingye Zhao, Xin Chen, Zhuoyu Zhao, Yifan Zhang, Enyi Tang, and Xuandong Li. Verifying neural network controlled systems using neural networks. In HSCC , pages 3:1--3:11. ACM , 2022. doi:10.1145/3501710.3519511
-
[42]
Henzinger, and Krishnendu Chatterjee
Dorde Zikelic, Mathias Lechner, Thomas A. Henzinger, and Krishnendu Chatterjee. Learning control policies for stochastic systems with reach-avoid guarantees. In AAAI , pages 11926--11935. AAAI Press, 2023. doi:10.1609/AAAI.V37I10.26407
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