REVIEW 1 major objections 1 minor 53 references
Reviewed by Pith at T0; open to challenge.
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T0 review · grok-4.3
Physics-informed neural networks perform similarly on shocks whether equations are written in conservative or non-conservative form.
2026-05-25 08:11 UTC pith:B2M5OOBF
load-bearing objection This is a straightforward empirical check on whether PINNs care about conservative vs non-conservative form for shocks, but the benchmarks stay inside the class where both forms exist. the 1 major comments →
Physics-Informed Neural Networks: Bridging the Divide Between Conservative and Non-Conservative Equations
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The work establishes that PINNs exhibit limited sensitivity to the conservative versus non-conservative formulation of the governing PDEs when applied to flows containing shocks and discontinuities, as demonstrated through systematic comparisons on the Burgers equation and both steady and unsteady Euler equations.
What carries the argument
Physics-Informed Neural Networks trained on residuals of the PDE in either conservative or non-conservative form, tested for shock-capturing accuracy on Burgers and Euler equations.
Load-bearing premise
The chosen benchmark problems sufficiently represent the numerical challenges posed by inherently non-conservative PDEs in complex physical phenomena such as multi-phase flows.
What would settle it
A clear and consistent drop in accuracy or increase in shock smearing when switching from conservative to non-conservative form on the Burgers or Euler test cases would falsify the claim of limited sensitivity.
If this is right
- PINNs could be applied directly to non-conservative formulations arising in multi-phase or other complex flows without needing to rewrite the equations.
- The usual restriction that standard numerical solvers impose on equation form would not apply to PINN-based solvers for these problems.
- Discontinuities in compressible flows could be handled by PINNs regardless of whether the underlying equations are presented in divergence or non-divergence form.
Where Pith is reading between the lines
- If the insensitivity holds, PINNs might reduce the need for specialized conservative-variable transformations that are common in traditional CFD codes.
- The same tests could be repeated on equations from other domains, such as non-conservative forms in magnetohydrodynamics or viscoelastic flows, to check generality.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript investigates the sensitivity of Physics-Informed Neural Networks (PINNs) to conservative versus non-conservative PDE formulations for problems involving shocks and discontinuities. It motivates the study by noting that many complex flows (e.g., multi-phase) are inherently non-conservative and conducts empirical tests on the Burgers equation together with steady and unsteady Euler equations.
Significance. If the empirical results were to show that PINNs are insensitive to formulation choice near discontinuities while traditional discretizations are not, the work would offer a practical route to handling non-conservative products without ad-hoc regularization. The current text, however, presents only the intent and benchmark list; no error metrics, loss curves, or comparative tables are supplied, so the significance cannot yet be evaluated.
major comments (1)
- [Abstract / Benchmark selection] The central claim that the chosen benchmarks 'provide a comprehensive understanding' of PINN behavior for inherently non-conservative systems rests on an untested assumption. Burgers and both Euler systems remain hyperbolic conservation laws that admit equivalent conservative and non-conservative forms; they therefore do not probe the structural difficulty of non-conservative products that cannot be rewritten in divergence form (the motivating case of multi-phase flows).
minor comments (1)
- [Abstract] The abstract states the investigative goal but supplies neither quantitative results nor error metrics; a results-oriented abstract would better convey the paper's contribution.
Simulated Author's Rebuttal
We thank the referee for their thoughtful comments. We address the major comment below and indicate where revisions will be made.
read point-by-point responses
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Referee: [Abstract / Benchmark selection] The central claim that the chosen benchmarks 'provide a comprehensive understanding' of PINN behavior for inherently non-conservative systems rests on an untested assumption. Burgers and both Euler systems remain hyperbolic conservation laws that admit equivalent conservative and non-conservative forms; they therefore do not probe the structural difficulty of non-conservative products that cannot be rewritten in divergence form (the motivating case of multi-phase flows).
Authors: We acknowledge that the referee's observation is correct. The Burgers equation and the Euler equations are hyperbolic conservation laws that admit mathematically equivalent conservative and non-conservative formulations. Our empirical tests therefore examine sensitivity to formulation choice within this class of problems rather than the stricter case of non-conservative products that cannot be expressed in divergence form. We will revise the abstract and introduction to remove the phrasing 'provide a comprehensive understanding' and to explicitly qualify the scope of the benchmarks, noting that they serve as an initial investigation into PINN behavior for shock-containing flows rather than a direct probe of inherently non-rewritable non-conservative systems. revision: yes
Circularity Check
No circularity: empirical benchmark study with no derivations or fitted predictions
full rationale
The paper presents an empirical investigation of PINN performance on Burgers and Euler equations in conservative vs. non-conservative forms. No derivation chain, fitted parameters renamed as predictions, self-citation load-bearing premises, or ansatz smuggling is present. The central claim rests on numerical experiments across stated benchmarks rather than any reduction of outputs to inputs by construction. The skeptic concern about benchmark representativeness is a question of external validity, not circularity.
Axiom & Free-Parameter Ledger
read the original abstract
In the realm of computational fluid dynamics, traditional numerical methods, which heavily rely on discretization, typically necessitate the formulation of partial differential equations (PDEs) in conservative form to accurately capture shocks and other discontinuities in compressible flows. Conversely, utilizing non-conservative forms often introduces significant errors near these discontinuities or results in smeared shocks. This dependency poses a considerable limitation, particularly as many PDEs encountered in complex physical phenomena, such as multi-phase flows, are inherently non-conservative. This inherent non-conservativity restricts the direct applicability of standard numerical solvers designed for conservative forms. This work aims to thoroughly investigate the sensitivity of Physics-Informed Neural Networks (PINNs) to the choice of PDE formulation (conservative vs. non-conservative) when solving problems involving shocks and discontinuities. We have conducted this investigation across a range of benchmark problems, specifically the Burgers equation and both steady and unsteady Euler equations, to provide a comprehensive understanding of PINNs capabilities in this critical area.
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