REVIEW 4 major objections 7 minor 39 references
Learning Hamiltonian Dynamics with Bayesian Data Assimilation
T0 review · 4 major / 7 minor · reviewed 2026-08-09 · deepseek-v4-flash
Pith's one-line read A Hamiltonian neural network trained on multi-step rollouts, coupled to an Unscented Kalman Filter, predicts long-horizon orbits while conserving energy.
desk verdict Useful combination of HNN+UKF for Molniya orbit prediction, but the evaluation needs error bars, a step-size check, and table cleanup before the claims are solid. 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 load-bearing object is the autoregressive Hamiltonian loss of Eq. (4), which treats the network as a map $F_\theta(x_k) = x_k + \int_{t_k}^{t_{k+1}} J\nabla H_\theta\,dt$ and trains it by unrolling $W$ composed copies of $F_\theta$ against the true trajectory segment. This makes the training objective match the closed-loop use of the model and penalizes error growth over exactly the horizon the model will be asked to predict. The second mechanism is the Unscented Kalman Filter, which propagates a set of $\sigma$ points through $F_\theta$, reconstructs mean and covariance, and corrects the state with measurements; this supplies both real-time refinement and uncertainty quantification. The paper also uses a Huber loss and a fourth-order Runge-Kutta integrator with a fixed 60-second step for the orbit experiments.
What would settle it
Re-run the orbit experiment on a test set where periapsis passages fall between the 60-second sample points, and compare AHNN5 predictions against a reference trajectory produced with an adaptive-step symplectic integrator; if the error spikes on those orbits or the energy drifts, the paper's claim that AHNN preserves invariants under its tested discretization fails.
Extended reading notes
Core claim
The paper's central claim is that the Hamiltonian structure of an unknown system can be learned from state sequences alone and then used as a predictive model that both conserves energy and maintains accuracy over long rollouts. The authors replace the standard HNN loss on state derivatives with an autoregressive loss, Eq. (4), that applies the learned flow $F_\theta$ recursively for $W$ steps and averages the distance between the predicted and observed states. They then insert this flow into an Unscented Kalman Filter that propagates $\sigma$ points through $F_\theta$ and assimilates noisy position measurements. In their numerical experiments, AHNN5 achieves the best RMSE among MLP, NODE, HNN, and AHNN variants, with the UKF version AHNNKF5 best overall, and the reported energy RMSE for AHNN5 is around two orders of magnitude smaller than for MLP and NODE. The paper thereby claims a practical recipe for learning Hamiltonian dynamics where derivative measurements such as accelerations are unavailable.
Load-bearing premise
The whole method rests on the assumption that a fixed 60-second Runge-Kutta step resolves the sharp periapsis acceleration of the Molniya orbit, so the learned Hamiltonian is not biased by the discretization.
Editorial extensions
If this is right
- If the central claim is correct, position-velocity telemetry alone is enough to train a prediction model that respects Hamiltonian structure, removing the need for noisy acceleration labels.
- The best-performing model, AHNNKF5, provides both a low-error state estimate and a covariance, which is what real orbit determination and collision-assessment pipelines need.
- Larger autoregressive windows improve prediction accuracy in the paper's ablations, at the cost of more expensive backpropagation through time; this gives practitioners a direct trade-off to tune.
- The reported energy conservation means predicted trajectories will not exhibit the artificial spiral-in or spiral-out seen with MLP and NODE baselines over long horizons.
Reading between the lines
- Editorial inference: the fixed 60-second Runge-Kutta step is part of what the network learns, so retraining with a symplectic or adaptive-step integrator is a direct test of whether the reported gains survive a different discretization.
- Editorial inference: the same AHNN-UKF recipe should transfer to other systems with known symplectic structure but unknown potentials, such as rigid-body rotation or charged-particle motion in a magnetic field, though the paper does not demonstrate this.
- Editorial inference: the paper's uncertainty bands come from the UKF's Gaussian approximation and may be optimistic under model mismatch; comparing the reported $3\sigma$ intervals against empirical error across many test orbits would quantify that.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes a Hamiltonian Neural Network (HNN) training objective that does not require state-derivative labels, an autoregressive extension (AHNN) that trains over multi-step rollouts, and a UKF-based Bayesian data assimilation scheme (AHNNKF) for state estimation and uncertainty quantification. The authors validate the approach on a frictionless mass-spring system and on highly elliptic, J2-perturbed Molniya orbits, reporting RMSE and energy-conservation metrics. The central claim is that AHNN5 and AHNNKF5 achieve the best long-term prediction accuracy while preserving physical invariants such as energy, and that the UKF integration improves robustness and provides uncertainty estimates. The paper does not ship code, and the empirical validation has several gaps that currently prevent full confidence in the central claim.
Significance. If the claims are substantiated, the paper makes a useful algorithmic contribution: it replaces derivative labels with one-step transitions, adds an autoregressive training objective that is particularly relevant to long-horizon prediction, and embeds the learned surrogate in a Bayesian filter to obtain state estimates with uncertainty. The orbital benchmark on highly elliptic Molniya orbits is a meaningful and nontrivial test case, and the energy-RMSE comparisons against MLP and NODE baselines are informative. However, the load-bearing empirical claims are not yet fully supported: the fixed 60-second RK4 step may alias the fast periapsis dynamics, no error bars are reported around the headline RMSE values, and the gravitational potential used for data generation is underspecified. The paper is potentially valuable, but it needs substantial additional validation and clarification before the main claims can be accepted.
major comments (4)
- [§5.2 and Eq. (3)] The fixed 60 s RK4 step used to define and train Fθ may alias the periapsis segment of the Molniya orbits, so the claim that the learned Hθ preserves the physical Hamiltonian is not established. Section 5.1.2 reports periapsis altitudes of 540–560 km and eccentricities 0.7–0.8, and Figure 1 notes speed variations of an order of magnitude; with h=60 s the RK4 local error near periapsis is uncontrolled, and because the training samples are exactly 60 s apart, Hθ can absorb the discretization error into an effective step-dependent Hamiltonian. The reported energy RMSE (Figure 7) therefore does not distinguish a physical Hamiltonian from a step-tuned discrete surrogate. I request an explicit discretization-convergence study: retrain and evaluate with h=30 s and h=120 s, or with an adaptive integrator at a fixed tolerance, and show that the induced energy error and test RMSE are stable across these choices.
- [§5.3, Tables 1–2] No error bars or variance information are reported for the central comparisons. Section 5.2 states that models are evaluated with three random seeds, but Tables 1 and 2 report single RMSE values; it is not stated whether these are the best, median, or mean of the seeds, and no standard deviation or confidence interval is given. This matters because several advertised improvements are small: for example, in Table 1, AHNNKF5 position RMSE (0.6596) is only about 10% below HNNKF (0.7261) in the true-initial mass-spring case. Please report the mean and standard deviation over seeds and over test orbits for all entries in Tables 1 and 2, and similarly for the energy RMSE values reported in the text.
- [§4.2, Eq. (13)] The gravitational potential used to generate the orbital data is underspecified. Equation (13) presents a full spherical-harmonic expansion with unspecified degrees Nz and Nt, defines longitude via arccos, and does not specify the rotation between the Earth-centered inertial frame in which (q,p) are expressed and the body-fixed frame in which the potential is evaluated; the text then states that only J2 is used, but does not say whether the training and evaluation data were generated with only J2 or with additional GGM05C terms. Please state precisely which potential was used for data generation and training, give the J2 value and frame conventions, and replace the arccos longitude definition with atan2(y,x) if any longitude-dependent tesseral terms are retained.
- [Table 2, NODE row] In Table 2, the NODE row reports perturbed-initial RMSE values of 14374 and 25121, which are two orders of magnitude larger than the true-initial values (124.66 and 84.067) and appear inconsistent with the scaling column header; the text discusses this only qualitatively as a lack of robustness. Please clarify how these values were computed, whether any divergent filtered trajectories were excluded or clipped, and whether the scaling of the table entries is the same for all models.
minor comments (7)
- [Tables 1–2] Tables 1 and 2 contain repeated digit strings such as '1.55281.55281.5528' and '1.73811.73811.7381'; if these are not formatting artifacts in the manuscript, the table entries need to be corrected.
- [§5.2] The sentence 'We use a fourth-order Runge-Kutta integrator with a fixed time step of 60 s' appears to apply to the orbital experiments, but the mass-spring experiment uses a 0.01 s sampling interval; clarify that the 60 s step applies only to the orbital experiments and specify the integration step used for the mass-spring system.
- [References] The reference for Brown (2004) is incomplete because it lacks a title, and the AdamW citation lists only Loshchilov; please provide the full references.
- [§5.2] The 'ExpHyperbolicLR' scheduler is cited to a preprint by the authors but is not described in the paper; either define the scheduler or remove the dependency on an unpublished external method.
- [Eq. (7)] In Eq. (7), Yk is described as the set of measurements 'until the time instant tk+1'; it should be tk, and the quantity δxk+1 should be defined before it is used in the covariance expression.
- [Algorithm 1] Algorithm 1 has no return statement; specify the outputs (x̂k+1, Pk+1) to make the pseudocode self-contained.
- [§3.2.2] The sigma-point generation is described as taking 'the i-th row of the matrix square root'; specify whether a Cholesky factor or a symmetric square root is used, since this affects the spread of the sigma points.
Circularity Check
No significant circularity: the neural surrogates are trained on external trajectory data and benchmarked against independent mass-spring and J2-perturbed orbit tests; the only self-citation is a peripheral learning-rate scheduler.
full rationale
The central derivation chain is self-contained. The surrogate Fθ in Eq. (3) is trained by minimizing the metric d(Fθ(xk), xk+1) in Eq. (2) and its autoregressive extension in Eq. (4) against externally generated trajectory pairs; no target output is reused to define the loss. The benchmarks are independent: the true mass-spring Hamiltonian (Eq. 11) and the J2-perturbed two-body Hamiltonian (Eqs. 12-13) are fixed simulation models, with training data produced by GL4/KahanLi8 symplectic integrators and test RMSE computed against true states and energies. Energy conservation is not a fitted target; it is a structural property of the J∇Hθ form, and the reported energy RMSE is evaluated against the known physical energy, so the HNN/AHNN conservation results are external evidence rather than reverse-engineered outputs. The autoregressive recursion appears in both the loss (Eq. 4) and the evaluation, but that is the intended multi-step training objective, not a hidden reuse of test labels. UKF tuning of (α,β,κ) on validation RMSE is standard hyperparameter selection, and the final comparisons are on held-out test trajectories. The only self-citation is the ExpHyperbolicLR scheduler (Kim, 2024), which is peripheral to the dynamics-learning claim and not load-bearing. No load-bearing step reduces to its own inputs, so the paper does not exhibit circularity.
Assumptions & free parameters
free parameters (5)
- Autoregressive window W =
5 (selected after ablation over {1,3,5})
- UKF sigma-point parameters (alpha, beta, kappa) =
not reported; tuned via TPE over 200 trials on validation RMSE
- Neural network architecture and optimizer hyperparameters =
not reported; chosen by search over layers, nodes, learning rates
- Fixed time step h for RK4 in Ftheta =
60 s
- Initial covariance P0 =
diag(10,10,1e-3,1e-3) for orbit; 1e-7*I for mass-spring
assumptions (5)
- domain assumption Hamilton's equations (1) with a time-independent Hamiltonian govern the unknown system; generalized coordinates q and conjugate momenta p are measured or inferred.
- ad hoc to paper The one-step map Ftheta computed by RK4 integration of J*grad(Htheta) over [t_k, t_{k+1}] is an accurate discrete-time surrogate of the true continuous flow.
- domain assumption Observation model H(.) is known and noise omega, eta are zero-mean Gaussian; state prior is Gaussian.
- domain assumption The J2-only gravitational potential adequately represents the training data and the test scenario.
- ad hoc to paper UKF covariance parameters (alpha, beta, kappa) selected by TPE yield a well-calibrated posterior.
Cite this review
Pith. "Pith review of Learning Hamiltonian Dynamics with Bayesian Data Assimilation." pith.science (2026). https://pith.science/paper/WABBFWML
@misc{pith2026250118808,
author = {Pith},
title = {Pith review of: Learning Hamiltonian Dynamics with Bayesian Data Assimilation},
year = {2026},
howpublished = {\url{https://pith.science/paper/WABBFWML}},
note = {Machine review of arXiv:2501.18808}
}
read the original abstract
In this paper, we develop a neural network-based approach for time-series prediction in unknown Hamiltonian dynamical systems. Our approach leverages a surrogate model and learns the system dynamics using generalized coordinates (positions) and their conjugate momenta while preserving a constant Hamiltonian. To further enhance long-term prediction accuracy, we introduce an Autoregressive Hamiltonian Neural Network, which incorporates autoregressive prediction errors into the training objective. Additionally, we employ Bayesian data assimilation to refine predictions in real-time using online measurement data. Numerical experiments on a spring-mass system and highly elliptic orbits under gravitational perturbations demonstrate the effectiveness of the proposed method, highlighting its potential for accurate and robust long-term predictions.
Figures
Figures from the paper (8 more)
Reference graph
Works this paper leans on
-
[1]
write newline
" write newline "" before.all 'output.state := FUNCTION n.dashify 't := "" t empty not t #1 #1 substring "-" = t #1 #2 substring "--" = not "--" * t #2 global.max substring 't := t #1 #1 substring "-" = "-" * t #2 global.max substring 't := while if t #1 #1 substring * t #2 global.max substring 't := if while FUNCTION format.date year duplicate empty "emp...
-
[2]
Iteration-free computation of gauss--legendre quadrature nodes and weights
Bogaert, I. Iteration-free computation of gauss--legendre quadrature nodes and weights. SIAM Journal on Scientific Computing, 36 0 (3): 0 A1008--A1026, 2014
work page 2014
-
[3]
Brown, R. G. Courier Corporation, 2004
work page 2004
-
[4]
Caldas, F. and Soares, C. Machine learning in orbit estimation: A survey. Acta Astronautica, 2024
work page 2024
-
[5]
T., Rubanova, Y., Bettencourt, J., and Duvenaud, D
Chen, R. T., Rubanova, Y., Bettencourt, J., and Duvenaud, D. K. Neural ordinary differential equations. Advances in neural information processing systems, 31, 2018
2018
-
[6]
Cheng, M., Ries, J. C., and Tapley, B. D. Variations of the earth's figure axis from satellite laser ranging and grace. Journal of Geophysical Research: Solid Earth, 116 0 (B1), 2011. doi:10.1029/2010JB000850
-
[7]
Structural schemes for hamiltonian systems
Clain, S., Franck, E., and Michel-Dansac, V. Structural schemes for hamiltonian systems, 2025. URL https://arxiv.org/abs/2501.13515
work page Pith review arXiv 2025
-
[8]
Galioto, N. and Gorodetsky, A. A. Bayesian identification of hamiltonian dynamics from symplectic data. In 2020 59th IEEE Conference on Decision and Control (CDC), pp.\ 1190--1195. IEEE, 2020
work page 2020
Show all 39 references
-
[9]
Hamiltonian neural networks
Greydanus, S., Dzamba, M., and Yosinski, J. Hamiltonian neural networks. Advances in neural information processing systems, 32, 2019
2019
-
[10]
K., et al
Gurfil, P., Seidelmann, P. K., et al. Celestial mechanics and astrodynamics: theory and practice, volume 436. Springer, 2016
2016
-
[11]
Hamilton, W. R. On a General Method of Expressing the Paths of Light, & of the Planets, by the Coefficients of a Characteristic Function. PD Hardy, 1833
-
[12]
Huber, P. J. Robust estimation of a location parameter. In Breakthroughs in statistics: Methodology and distribution, pp.\ 492--518. Springer, 1992
1992
-
[13]
Julier, S. J. and Uhlmann, J. K. New extension of the kalman filter to nonlinear systems. In Signal processing, sensor fusion, and target recognition VI, volume 3068, pp.\ 182--193. Spie, 1997
1997
-
[14]
and Li, R.-C
Kahan, W. and Li, R.-C. Composition constants for raising the orders of unconventional schemes for ordinary differential equations. Mathematics of computation, 66 0 (219): 0 1089--1099, 1997
1997
-
[15]
Kalman, R. E. A new approach to linear filtering and prediction problems. Transactions of the ASME--Journal of Basic Engineering, 82 0 (Series D): 0 35--45, 1960
1960
-
[16]
L., Scott, K
Kazemi, S., Azad, N. L., Scott, K. A., Oqab, H. B., and Dietrich, G. B. Orbit determination for space situational awareness: A survey. Acta Astronautica, 2024
2024
-
[17]
Hyperboliclr: Epoch insensitive learning rate scheduler
Kim, T.-G. Hyperboliclr: Epoch insensitive learning rate scheduler. arXiv preprint arXiv:2407.15200, 2024
2024 arXiv
-
[18]
and Waldherr, S
K \"u per, A. and Waldherr, S. Numerical gaussian process kalman filtering for spatiotemporal systems. IEEE Transactions on Automatic Control, 68 0 (5): 0 3131--3138, 2022
2022
-
[19]
Leonard, N. E. Mechanics and nonlinear control: Making underwater vehicles ride and glide. IFAC Proceedings Volumes, 31 0 (17): 0 1--6, 1998
1998
-
[20]
Decoupled weight decay regularization
Loshchilov, I. Decoupled weight decay regularization. arXiv preprint arXiv:1711.05101, 2017
2017 arXiv
-
[21]
E., Sood, R., and Su, W
Loshelder, G. E., Sood, R., and Su, W. Orbit determination using physics-informed neural networks. In AIAA SCITECH 2025 Forum, pp.\ 1931, 2025
2025
-
[22]
Beyond finite layer neural networks: Bridging deep architectures and numerical differential equations
Lu, Y., Zhong, A., Li, Q., and Dong, B. Beyond finite layer neural networks: Bridging deep architectures and numerical differential equations. In International Conference on Machine Learning, pp.\ 3276--3285. PMLR, 2018
2018
-
[23]
Hamiltonian mechanics and neural network technology for high stabilization of quadrotor uav on se (3)
Mohamed, B., Abdelkader, M., Mohammed, B., Lamaari, H., et al. Hamiltonian mechanics and neural network technology for high stabilization of quadrotor uav on se (3). In 2022 IEEE 3rd International Conference on Electronics, Control, Optimization and Computer Science (ICECOCS),...
2022
-
[24]
Initial orbit determination methods for track-to-track association
Pastor, A., Sanjurjo-Rivo, M., and Escobar, D. Initial orbit determination methods for track-to-track association. Advances in Space Research, 68 0 (7): 0 2677--2694, 2021
2021
-
[25]
Pytorch: An imperative style, high-performance deep learning library
Paszke, A., Gross, S., Massa, F., Lerer, A., Bradbury, J., Chanan, G., Killeen, T., Lin, Z., Gimelshein, N., Antiga, L., et al. Pytorch: An imperative style, high-performance deep learning library. Advances in neural information processing systems, 32, 2019
2019
-
[26]
and Bai, X
Peng, H. and Bai, X. Artificial neural network--based machine learning approach to improve orbit prediction accuracy. Journal of Spacecraft and Rockets, 55 0 (5): 0 1248--1260, 2018
2018
-
[27]
and Bai, X
Peng, H. and Bai, X. Comparative evaluation of three machine learning algorithms on improving orbit prediction accuracy. Astrodynamics, 3 0 (4): 0 325--343, 2019
2019
-
[28]
and Karniadakis, G
Raissi, M. and Karniadakis, G. E. Hidden physics models: Machine learning of nonlinear partial differential equations. Journal of Computational Physics, 357: 0 125--141, 2018
2018
-
[29]
Raissi, M., Perdikaris, P., and Karniadakis, G. E. Multistep neural networks for data-driven discovery of nonlinear dynamical systems. arXiv preprint arXiv:1801.01236, 2018
2018 arXiv
-
[30]
Raissi, M., Perdikaris, P., and Karniadakis, G. E. Physics-informed neural networks: A deep learning framework for solving forward and inverse problems involving nonlinear partial differential equations. Journal of Computational physics, 378: 0 686--707, 2019
2019
-
[31]
and Haber, E
Ruthotto, L. and Haber, E. Deep neural networks motivated by partial differential equations. Journal of Mathematical Imaging and Vision, 62 0 (3): 0 352--364, 2020
2020
-
[32]
Salleh, N., Yuhaniz, S., and Azmi, N. M. Modeling orbital propagation using regression technique and artificial neural network. Int. J. Adv. Sci. Eng. Inf. Technol, 12 0 (3): 0 1279, 2022
2022
-
[33]
A physic-informed neural network approach to orbit determination
Scorsoglio, A., Ghilardi, L., and Furfaro, R. A physic-informed neural network approach to orbit determination. The Journal of the Astronautical Sciences, 70 0 (4): 0 25, 2023
2023
-
[34]
S., V \"a lisuo, P., Bhuiyan, M
Selvan, K., Siemuri, A., Prol, F. S., V \"a lisuo, P., Bhuiyan, M. Z. H., and Kuusniemi, H. Precise orbit determination of leo satellites: a systematic review. GPS Solutions, 27 0 (4): 0 178, 2023
2023
-
[35]
Orbit propagation from historical data using physics-informed neural odes
Subramanian, S., Ramnani, R., Sengupta, S., and Yadav, S. Orbit propagation from historical data using physics-informed neural odes. In 2023 International Conference on Machine Learning and Applications (ICMLA), pp.\ 1643--1648. IEEE, 2023
2023
-
[36]
Wan, E. A. and Van Der Merwe, R. The unscented kalman filter for nonlinear estimation. In Proceedings of the IEEE 2000 adaptive systems for signal processing, communications, and control symposium (Cat. No. 00EX373), pp.\ 153--158. Ieee, 2000
2000
-
[37]
M., Wiese, D
Watkins, M. M., Wiese, D. N., Yuan, D.-N., Boening, C., and Landerer, F. W. Improved methods for observing earth's time variable mass distribution with grace using spherical cap mascons. Journal of Geophysical Research: Solid Earth, 120 0 (4): 0 2648--2671, 2015
2015
-
[38]
and Belda, K
Z \'a da, V. and Belda, K. Mathematical modeling of industrial robots based on hamiltonian mechanics. In 2016 17th International Carpathian Control Conference (ICCC), pp.\ 813--818. IEEE, 2016
2016
-
[39]
A lstm assisted orbit determination algorithm for spacecraft executing continuous maneuver
Zhou, X., Qin, T., Ji, M., and Qiao, D. A lstm assisted orbit determination algorithm for spacecraft executing continuous maneuver. Acta Astronautica, 204: 0 568--582, 2023
2023
Reviewed August 9, 2026 · model on record in the stance chip above.
Discussion (0). Continue with ORCID to comment.