REVIEW 5 major objections 5 minor 23 references
A Modified Adaptive Data-Enabled Policy Optimization Control to Resolve State Perturbations
T0 review · 5 major / 5 minor · reviewed 2026-08-15 · deepseek-v4-flash
Pith's one-line read A modified DeePO algorithm claims full-rank data and calm states without probing noise.
desk verdict A well-motivated heuristic for removing probing noise from DeePO, but the full-rank proof has a fatal gap and the stability theorem doesn't match the algorithm. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The central object is the data covariance Φ = (1/t)DD^T built from stacked input-state data; its full rank is exactly the persistency-of-excitation condition that lets DeePO invert Φ and update the gain. PFDeePO wraps this in two mechanisms: a pause rule keyed to ‖x_i‖ ≤ γ that prevents uninformative zero columns from entering the dataset, and a multiplicative random gain v_i on the control signal, triggered only when the gain update ‖ΔK‖ has fallen below δ. The stability guarantee rests on the interval [v,v] from Lemma 5 and the modified DARE (31), whose solution H yields the exponential bound ‖x_k‖ ≤ β^k $\sqrt$(λmax(H)/λmin(H))‖x_0‖ for any v_k in the interval.
What would settle it
Run Algorithm 2 on the paper's four-state system with zero initial gain, no process noise, and no external disturbance; if the state norm drops below γ before ‖K_i − K*‖ approaches zero, the gain error or σ(Φ_i) will plateau, showing that the pause rule can stop learning before convergence.
Extended reading notes
Core claim
The paper claims that PFDeePO resolves the DeePO excitation dilemma by separating two failure regimes. When states converge to the equilibrium, appending them to the data matrix drives the minimum singular value of the sample covariance Φ to zero; PFDeePO stops updating the gain in this regime. When the gain has already converged but states are still far from equilibrium, the algorithm multiplies the control signal by a random scalar v_i drawn from an interval [v,v] with v < 1 < v, ensuring newly appended columns keep the data matrix full rank. The paper proves in Theorem 1 that Φ_i stays full rank under Algorithm 2, and in Theorem 2 that any sequence v_i in that interval preserves exponential stability of the closed loop via a modified DARE and a quadratic Lyapunov function. Simulations on a four-state system show states remaining at equilibrium after a disturbance, while σ(Φ_i) stays bounded away from zero.
Load-bearing premise
The method assumes that in the noiseless pre-convergence phase, state-feedback data remain informative enough for the DeePO gradient update to make progress before the pause rule triggers; if a stable plant drives the state to equilibrium first, learning can stall before the optimal gain is reached.
Editorial extensions
If this is right
- Adaptive LQR can in principle run without continuous probing noise, eliminating the persistent dither that wears actuators and disturbs states.
- The inverse Φ^{-1} in the DeePO update remains well-defined at every iteration because σ(Φ_i) is kept positive by the pause-and-scale logic.
- When the random scaling is active, the closed loop stays exponentially stable for any sequence of gains in the allowed interval, so the added excitation does not sacrifice stability.
- Near equilibrium, the gain update is frozen, so the algorithm stops spending control effort on data points that carry no new information.
- The simulation comparison shows PFDeePO settling states after a disturbance while DeePO with probing noise keeps oscillating and increasing control effort.
Reading between the lines
- An immediate testable extension is to replace the threshold heuristics γ and δ with a direct monitor of σ(Φ_i), pausing only when the data actually lose informativeness; this could remove two hand-tuned parameters.
- If a stable open-loop plant drives the state to equilibrium before the gain has converged, the pause rule can stall learning altogether; the paper does not analyze that pre-convergence stall, and adding a bounded external disturbance or retaining a few persistently exciting offline columns would be a natural workaround.
- The interval [v,v] could be selected online from a data-driven estimate of B via the pseudoinverse formula in Remark 2, making the stability certificate adaptive rather than fixed, at the price of needing an accurate B estimate.
- The same pause-and-scale idea may carry over to output-feedback or nonlinear extensions of DeePO, but those settings would need their own Lyapunov or observability assumptions, not just the LTI DARE argument.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes PFDeePO, a modified version of the data-enabled policy optimization (DeePO) algorithm for adaptive LQR, with the goal of avoiding the state perturbations caused by probing noise. The algorithm combines a pause rule that stops gain updates when the state is near equilibrium with a multiplicative random gain applied once the controller has approximately converged. The paper claims two main theoretical results: Theorem 1 states that PFDeePO preserves the full rank of the data matrix Φ, and Theorem 2 establishes exponential stability of the closed loop under the random scaling. The claims are supported by a numerical example comparing PFDeePO with DeePO with and without probing noise.
Significance. If the central claims were established, the contribution would be practically useful: it would let DeePO-style adaptive LQR run without persistent input excitation after convergence, reducing state chattering and actuator wear. The paper correctly identifies a real limitation of DeePO, namely that LQR state feedback cannot generate persistently exciting inputs, and the simulation qualitatively illustrates the intended benefit. However, the two theoretical pillars are not sound as written. The proof of Theorem 1 contains an invalid inference that requires an unstated spanning condition, Lemma 4 points to a mechanism by which the first branch of Algorithm 2 can drive σ(Φ) to zero, and Theorem 2 conflates the standard LQR DARE gain with a different gain defined by a modified DARE. The stability analysis also relies on an interval [v,v] whose existence is asserted but not constructively verified for the actual system data. The paper does not provide reproducible code or machine-checked proofs, and the simulation alone does not compensate for the gaps in the theory.
major comments (5)
- [Theorem 1, Section III] The inference from equations (23)-(24) to equation (25) is invalid. From (24) one obtains, for each k, the relation ∑_i (λ_i - ∑_j μ_j K_{j,i}^{(k)}) x_i^{(k)} = 0, which implies λ = (K^{(k)})^T μ only if the vectors x^{(k)} span R^n. No such spanning condition is stated or proven, and for a stable open-loop plant the states typically decay and may lie near a low-dimensional subspace. Moreover, the row dependence (23) involves all columns of X0 and U0, including the initial offline persistently exciting columns, whereas the substitution U0_{j,k} = ∑_i K_{j,i}^{(k)} x_i^{(k)} applies only to online columns generated by state feedback. The contradiction in Theorem 1 therefore does not follow.
- [Lemma 4 and Algorithm 2, Section III] Lemma 4 shows that appending a rank-deficient block D2 drives σ(Φ) to zero. In Algorithm 2, whenever ∥ΔK∥ > δ and ∥x_i∥ > γ, the control is u_i = K_i x_i with no stochastic excitation, and the resulting column is appended to the dataset. By Lemma 3 these columns are rank-deficient, so σ(Φ_i) can be driven toward zero before the gain converges. Theorem 1 does not establish a positive lower bound on σ(Φ_i), and it cannot, because the first branch of Algorithm 2 is exactly the regime covered by Lemma 4. The pause rule does not fix this: it stops appending data only when ∥x_i∥ ≤ γ, not when ∥ΔK∥ > δ.
- [Theorem 2, Equations (26)-(31)] Theorem 2 defines the converged gain K through the modified DARE (31) with β ∈ (0,1), but the DeePO/LQR gain referenced in (26)-(27) solves the standard DARE, which corresponds to β = 1. Unless β = 1, these gains are different, so the key identity (37), on which the Lyapunov decrease (38) relies, does not hold for the actual DeePO gain. The statement that 'K is equal to a certainly equivalent LQR gain' is therefore inconsistent with (31) for β < 1. The existence and uniqueness of a positive definite solution H to the modified DARE (31) is also assumed without proof.
- [Algorithm 2, Remark 1, Section IV] The instruction 'Find v and v as in Theorem 2 for Ki' is not implementable as stated. It requires the solution H of the modified DARE (31) and verification of the matrix inequality (28), but no data-driven procedure is given to compute H or to certify (28) from measured data. Remark 1's iterative narrowing is not a concrete check, since no estimate of H is supplied. The simulation states that the interval [0.5,1.5] 'satisfies (28)' without presenting the verification, so the stability guarantee is not actually demonstrated for the reported experiment.
- [Section IV, simulation setup] For the open-loop stable plant with initial gain K_t = 0, the state decays toward the equilibrium. If ∥x_i∥ ≤ γ is reached while ∥ΔK∥ > δ, the second if-else block freezes the gain K_{i+1} = K_i and stops appending data, so learning stalls permanently before the gain converges. The simulation avoids this by injecting a disturbance at sample k = 15, but Algorithm 2 contains no mechanism that guarantees the gain converges before the state enters the γ-ball. This is a load-bearing gap because the paper's central claim is that PFDeePO works without probing noise.
minor comments (5)
- [Throughout] There are several language and typography issues: 'certainly equivalent' should be 'certainty-equivalent', 'Perturbations-free' should be 'Perturbation-free', and the author block contains a stray space in 'V .'.
- [Equation (15)] The notation in (15) is unclear: the bar notation for U0, X0, and X1 is introduced informally, and the relationship between Φ = (1/t)DD^T and the subsequent X1 = X1D^T/t is not defined cleanly. Please define all overlined quantities explicitly.
- [Section IV] The disturbance at sample k = 15 is described only as 'a uniform random value'; its dimension, range, and whether the reported results are from a single run or averaged over multiple runs should be specified.
- [Figure 2] The curve labeled 'DeePO without e' is not covered by Algorithm 1, since Algorithm 1 requires a probing noise signal and Φ may become singular without it. The implementation of this benchmark should be described, particularly the matrix inversion step.
- [Theorem 2, Equation (32)] The closed-loop stability result is stated for the estimated matrices (Â,B̂), but the relationship between these estimates and the true system (1) is not discussed. The practical relevance of the bound (33) for the true plant is therefore unclear.
Circularity Check
No significant circularity: PFDeePO's rank and stability arguments do not reduce to their own inputs or to load-bearing self-citations.
full rationale
The paper's central claims are that Algorithm 2 preserves the full rank of Φ and that the multiplicative-noise control v_k K_k x_k preserves closed-loop stability. Neither claim is circular. The rank preservation argument in Theorem 1 is a attempted proof by contradiction on rank(D); although the step from (24) to (25) requires the state samples to span R^n, which is not stated or proven, this is a proof gap and a correctness risk, not a definitional equivalence or a fitted input renamed as a prediction. The stability argument in Theorem 2 is a standard Lyapunov argument using the modified DARE (31) and the sufficient interval condition (28); the interval [v,v] is not fitted to simulation outcomes but is presented as satisfying a matrix inequality, and the theorem's conclusion does not coincide with its assumptions. The citation to the DeePO equivalence result (Lemma 1 of [16]) is to work by different authors (Zhao, Dörfler, Chiuso, You), not to the present authors, so it is not a load-bearing self-citation. The self-citations in the paper ([14], [18]) are contextual references to prior bicycle work and are not used to supply assumptions to the central theorems. The simulation parameters (γ=0.1, δ=0.1, v=0.5, v=1.5) are asserted to satisfy (28) without a shown verification, and the role of β in Algorithm 2 is unclear, but these are reproducibility and correctness concerns rather than instances where an output is equivalent to an input by construction. Therefore the circularity score is 0.
Assumptions & free parameters
free parameters (6)
- gamma =
0.1
- delta =
0.1
- v and v (multiplicative scaling interval) =
0.5 and 1.5
- eta (learning rate) =
10^-4
- sigma_e (probing noise std for DeePO baseline) =
0.1
- beta (discount factor in Theorem 2)
assumptions (5)
- ad hoc to paper There exists a unique positive definite solution H to the modified DARE (31) for the chosen beta in (0,1).
- ad hoc to paper The interval [v,v] used in Algorithm 2 satisfies the matrix inequality (28) for the actual system data.
- domain assumption The pre-convergence phase of Algorithm 2, with u_i = K_i x_i and no probing noise, preserves the conditioning of Phi and the descent property of the DeePO update.
- standard math The offline data (U0, X0, X1) are generated by a persistently exciting input of order n+1, so that rank(D)=n+m initially.
- domain assumption The pair (A,B) is controllable and the noise omega_k is bounded.
Cite this review
Pith. "Pith review of A Modified Adaptive Data-Enabled Policy Optimization Control to Resolve State Perturbations." pith.science (2026). https://pith.science/paper/RODWGGK5
@misc{pith2026250720580,
author = {Pith},
title = {Pith review of: A Modified Adaptive Data-Enabled Policy Optimization Control to Resolve State Perturbations},
year = {2026},
howpublished = {\url{https://pith.science/paper/RODWGGK5}},
note = {Machine review of arXiv:2507.20580}
}
abstract
This paper proposes modifications to the data-enabled policy optimization (DeePO) algorithm to mitigate state perturbations. DeePO is an adaptive, data-driven approach designed to iteratively compute a feedback gain equivalent to the certainty-equivalence LQR gain. Like other data-driven approaches based on Willems' fundamental lemma, DeePO requires persistently exciting input signals. However, linear state-feedback gains from LQR designs cannot inherently produce such inputs. To address this, probing noise is conventionally added to the control signal to ensure persistent excitation. However, the added noise may induce undesirable state perturbations. We first identify two key issues that jeopardize the desired performance of DeePO when probing noise is not added: the convergence of states to the equilibrium point, and the convergence of the controller to its optimal value. To address these challenges without relying on probing noise, we propose Perturbation-Free DeePO (PFDeePO) built on two fundamental principles. First, the algorithm pauses the control gain updating in DeePO process when system states are near the equilibrium point. Second, it applies a multiplicative noise, scaled by a mean value of $1$ as a gain for the control signal, when the controller converges. This approach minimizes the impact of noise as the system approaches equilibrium while preserving stability. We demonstrate the effectiveness of PFDeePO through simulations, showcasing its ability to eliminate state perturbations while maintaining system performance and stability.
Figures
Reference graph
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Reviewed August 15, 2026 · model on record in the stance chip above.
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