Trajectory-based Safety of Monotone Systems: Verification and Control Synthesis
Pith reviewed 2026-05-20 15:27 UTC · model grok-4.3
The pith
For monotone systems, dominance functions built from arbitrary trajectories serve as dissipative safety certificates.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
Dominance functions constructed from collected trajectories of monotone discrete-time systems are dissipative, meaning they decrease monotonically along system trajectories, and are sufficiently expressive to characterize safety certificates for both robust verification and safe control synthesis.
What carries the argument
Dominance functions, constructed from arbitrary collected trajectories and used as building blocks whose linear combinations yield safety certificates once monotonicity ensures dissipativity.
If this is right
- Safety certificates for verification can be found by optimizing over linear combinations of a small number of dominance functions.
- Safe control inputs can be synthesized by the same optimization while respecting the monotone structure.
- Formal guarantees hold even when the collected trajectories themselves violate the safety specification.
- Data requirements drop sharply compared with non-structural data-driven methods because monotonicity supplies the needed monotonic decrease property.
Where Pith is reading between the lines
- The same dominance-function construction may apply to continuous-time monotone systems if the dissipativity argument carries over to differential equations.
- Systems with other order-preserving properties, such as positive systems, could admit analogous trajectory-based certificates.
- The sampling-based search could be replaced by a convex program if the dominance functions are restricted to particular parametric families.
Load-bearing premise
The system dynamics must be monotone with respect to a partial order.
What would settle it
A single trajectory in a claimed monotone system along which a constructed dominance function increases would falsify the dissipativity property.
Figures
read the original abstract
This paper presents a novel data-driven framework for the robust safety verification and safe control synthesis of unknown monotone discrete-time systems. While existing data-driven safety analysis approaches are often either heuristic in nature or require large amounts of data to provide rigorous guarantees, we leverage the structural property of monotonicity to significantly reduce data requirements while still ensuring formal safety guarantees. Our approach is built upon a new class of certificates called dominance functions, constructed directly from collected system trajectories, which themselves need not be safe. By exploiting the monotone structure of the dynamics, we show that dominance functions are (i) dissipative, meaning that they decrease monotonically along system trajectories, and (ii) sufficiently \expressive to characterize safety certificates for monotone systems. Together, these properties establish dominance functions as principled building blocks for the systematic construction of formal safety certificates directly from trajectory data. For both robust safety verification and safe control synthesis, we develop an efficient sampling-based optimization framework that searches for safety certificates represented as linear combinations of dominance functions constructed from collected trajectories. We validate our data-driven framework on two monotone systems by successfully deriving safety certificates from a small number of trajectories.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper presents a data-driven framework for robust safety verification and safe control synthesis of unknown monotone discrete-time systems. Dominance functions are constructed directly from (possibly unsafe) collected trajectories; monotonicity of the dynamics is used to prove that these functions are dissipative (decrease monotonically along trajectories) and sufficiently expressive to serve as building blocks for formal safety certificates via linear combinations. An efficient sampling-based optimization is developed to search for such certificates, with validation on two monotone systems using small numbers of trajectories.
Significance. If the central claims hold, the work provides a principled way to obtain formal safety guarantees with substantially reduced data requirements by exploiting monotonicity, a structural property common in many application domains. This could advance data-driven methods in control theory by bridging trajectory data to rigorous certificates without relying on large datasets or purely heuristic approaches.
major comments (2)
- [§3.3, Theorem 1] §3.3, Theorem 1: The dissipativity proof for dominance functions constructed from arbitrary trajectories relies on the monotonicity assumption, but the argument does not explicitly address the case where the comparison trajectory used in the dominance definition is itself generated under the same monotone dynamics; a concrete counter-example or additional step would strengthen the claim that V decreases for all system trajectories.
- [§4.2, Eq. (12)] §4.2, Eq. (12): The optimization formulation for control synthesis searches over linear combinations of dominance functions, yet the feasibility guarantee from the expressiveness result in Theorem 2 is stated only for verification; it is unclear whether the same linear-span argument directly transfers to the synthesis case when the input set is constrained.
minor comments (3)
- [Notation] Notation: The dominance function is denoted differently across sections (e.g., D vs. V); a single consistent symbol and definition reference would improve readability.
- [§5] §5, experimental section: The validation uses a small number of trajectories, but lacks a direct comparison table against non-monotone data-driven baselines to quantify the claimed reduction in data requirements.
- [References] References: Consider adding a citation to standard results on monotone dynamical systems (e.g., Smith 1995 or Hirsch & Smith 2005) to contextualize the structural assumption.
Simulated Author's Rebuttal
We thank the referee for the careful reading and constructive comments on our manuscript. We address each major comment below.
read point-by-point responses
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Referee: [§3.3, Theorem 1] The dissipativity proof for dominance functions constructed from arbitrary trajectories relies on the monotonicity assumption, but the argument does not explicitly address the case where the comparison trajectory used in the dominance definition is itself generated under the same monotone dynamics; a concrete counter-example or additional step would strengthen the claim that V decreases for all system trajectories.
Authors: We thank the referee for this observation. The definition of a dominance function in §3.3 is constructed from a pair of trajectories of the system, so the comparison trajectory is necessarily generated by the same dynamics. Monotonicity then guarantees that if x(0) ≼ y(0) then x(k) ≼ y(k) for every k, which is the key step used to establish that V decreases along any trajectory. To make the argument fully explicit we will insert a short clarifying sentence immediately after the statement of Theorem 1, noting that both trajectories satisfy the monotone dynamics. This is a minor clarification that does not change the result. revision: yes
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Referee: [§4.2, Eq. (12)] The optimization formulation for control synthesis searches over linear combinations of dominance functions, yet the feasibility guarantee from the expressiveness result in Theorem 2 is stated only for verification; it is unclear whether the same linear-span argument directly transfers to the synthesis case when the input set is constrained.
Authors: The referee is right that Theorem 2 is stated for the verification setting. In the synthesis formulation (12) the linear combination is still taken from the same span of dominance functions, but the search is now performed jointly with admissible control sequences that respect the input constraints. Because the dominance functions themselves are independent of the particular control law, the same density argument used in Theorem 2 continues to guarantee that a suitable combination exists whenever a control-invariant safety certificate exists; the input constraints are enforced directly by the optimizer rather than by the span. We will add a brief remark after Theorem 2 that explicitly notes this extension to the synthesis case. This is a partial revision consisting of one clarifying paragraph. revision: partial
Circularity Check
No significant circularity
full rationale
The central derivation establishes dissipativity and expressiveness of dominance functions from the external structural assumption of monotonicity in the system dynamics, which is not defined in terms of the safety certificates or dominance functions themselves. Trajectory data is used to construct the functions, but the key properties (i) and (ii) are proven by exploiting monotonicity rather than by fitting or self-referential construction. No load-bearing steps reduce by definition or self-citation to the inputs; the claims remain independent of the target safety certificates.
Axiom & Free-Parameter Ledger
axioms (1)
- domain assumption The unknown discrete-time system dynamics are monotone.
invented entities (1)
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dominance functions
no independent evidence
Lean theorems connected to this paper
-
IndisputableMonolith/Cost/FunctionalEquation.leanwashburn_uniqueness_aczel (J-cost uniqueness) unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
By exploiting the monotone structure of the dynamics, we show that dominance functions are (i) dissipative, meaning that they decrease monotonically along system trajectories, and (ii) sufficiently expressive to characterize safety certificates for monotone systems.
-
IndisputableMonolith/Foundation/RealityFromDistinction.leanreality_from_one_distinction unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
Theorem 1 (Properties of Dominance functions) … (Dissipation) … P̃x(f(x,w)) ≤ P̃x(x) …
What do these tags mean?
- matches
- The paper's claim is directly supported by a theorem in the formal canon.
- supports
- The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
- extends
- The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
- uses
- The paper appears to rely on the theorem as machinery.
- contradicts
- The paper's claim conflicts with a theorem or certificate in the canon.
- unclear
- Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.
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discussion (0)
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