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arxiv: 2605.24275 · v1 · pith:BXGQSS3Xnew · submitted 2026-05-22 · 📡 eess.SY · cs.SY

Learning regime-dependent governing equations: A symbolic decision tree approach

Pith reviewed 2026-06-30 14:14 UTC · model grok-4.3

classification 📡 eess.SY cs.SY
keywords symbolic decision treesregime-dependent governing equationsmixed-integer optimizationhybrid dynamical modelspolymer melts viscositydata-driven discoveryinterpretable modelschemical engineering systems
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The pith

Symbolic decision trees jointly learn regime partitions and local governing equations by solving a mixed-integer optimization problem.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

Chemical engineering systems often switch between different governing mechanisms depending on operating conditions. The paper develops symbolic decision trees that discover both the conditions splitting data into regimes and the equations holding inside each regime at the same time. Parametrizing the splits and the local equations with basis functions converts the task into a mixed-integer optimization problem solvable from data. The resulting models are intended to be more accurate than a single global equation and more interpretable than conventional decision trees, with demonstrations on hybrid dynamical systems and polymer-melt viscosity.

Core claim

Symbolic decision trees identify physically interpretable regimes and local governing equations while improving predictive accuracy relative to approaches that learn a single global model or use existing decision tree models. The method simultaneously learns interpretable splitting conditions to partition the input domain and local governing equations that describe each regime. Both the splitting conditions and governing equations are parametrized using basis functions, resulting in a mixed-integer optimization learning problem.

What carries the argument

Symbolic decision trees that parametrize splitting conditions for regime partitions and local governing equations with basis functions and solve the resulting mixed-integer optimization problem.

If this is right

  • The learned models support predictive modeling, optimization, and control in chemical engineering systems with regime switches.
  • The partitions and equations recovered are physically interpretable.
  • The same procedure applies to learning hybrid dynamical models.
  • The same procedure applies to learning constitutive equations such as zero-shear viscosity of polymer melts.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The framework could be tested on regime-switching data from domains outside chemical engineering where labeled regime data are scarce.
  • Changing the choice or number of basis functions might allow the same optimization structure to handle qualitatively different regime transitions without altering the algorithm.

Load-bearing premise

Parametrizing both splitting conditions and local governing equations with basis functions yields a tractable mixed-integer optimization problem whose solution correctly recovers the underlying regime partitions and equations from data.

What would settle it

Apply the method to data generated from a known regime-switching system with documented boundaries and equations; the recovered partitions or equations should match the known structure or at least reduce prediction error below that of a single global model.

Figures

Figures reproduced from arXiv: 2605.24275 by Gabriel E. Sanoja, Ilias Mitrai, Tongjia Liu.

Figure 1
Figure 1. Figure 1: Decision trees with nonlinear expressions in the leaves and splitting [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Mean absolute error on the testing set as a function of the number of [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Mean absolute error on the testing set as a function of the distance from the origin for the di [PITH_FULL_IMAGE:figures/full_fig_p005_3.png] view at source ↗
Figure 5
Figure 5. Figure 5: Schematic of the interacting two-tank system. [PITH_FULL_IMAGE:figures/full_fig_p005_5.png] view at source ↗
Figure 7
Figure 7. Figure 7: We simulate the system for t ∈ [0, 20] using [h1(0) h2(0)] = [0.1 1.2] as initial condition. From the results, we observe that the model discovered with the proposed approach tracks the evolution of height more accurately than the model discovered using sparse regression. Specifically, the root mean squared er￾ror with the proposed approach is 9.6 × 10−4 , whereas with the sparse regression model it is 2.5… view at source ↗
Figure 6
Figure 6. Figure 6: Inlet flow rates and liquid level evolution [PITH_FULL_IMAGE:figures/full_fig_p006_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: Evolution of the liquid level in the first tank using the model discovered with the proposed approach and with sparse regression. [PITH_FULL_IMAGE:figures/full_fig_p007_7.png] view at source ↗
Figure 8
Figure 8. Figure 8: Polymer viscosity as a function of molecular weight for [PITH_FULL_IMAGE:figures/full_fig_p007_8.png] view at source ↗
Figure 9
Figure 9. Figure 9: L2 error for the identified coefficients as a function of the noise level. 0.01 0.1 0.2 0.5 Noise level 10 3 10 2 10 1 Splitting condition coefficient recovery error [PITH_FULL_IMAGE:figures/full_fig_p008_9.png] view at source ↗
Figure 10
Figure 10. Figure 10: L2 error for the identified coefficients in the splitting conditions as a function of the noise level. 6. Conclusions In this paper, we propose a data-driven framework for dis￾covering regime-dependent governing equations. The major challenge in such learning tasks is the need to simultaneously identify distinct regimes and the governing equations within each regime. To address this challenge, we represen… view at source ↗
read the original abstract

Many chemical engineering systems are governed by mechanisms that switch across operating regimes, making the data-driven discovery of regime-dependent governing equations essential for predictive modeling, optimization, and control. We propose symbolic decision trees for the data-driven discovery of regime-dependent governing equations. The method simultaneously learns interpretable splitting conditions to partition the input domain and local governing equations that describe each regime. To improve tractability, both the splitting conditions and governing equations are parametrized using basis functions, resulting in a mixed-integer optimization learning problem. We use the proposed approach to learn hybrid dynamical models and a constitutive equation for the zero-shear viscosity of polymer melts. Symbolic decision trees identify physically interpretable regimes and local governing equations while improving predictive accuracy relative to approaches that learn a single global model or use existing decision tree models. This framework provides an interpretable and generalizable route for discovering regime-dependent models in chemical engineering systems.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 1 minor

Summary. The paper proposes symbolic decision trees to discover regime-dependent governing equations by simultaneously learning interpretable splitting conditions and local governing equations. Both are parametrized with basis functions to yield a mixed-integer optimization problem, which is applied to hybrid dynamical models and a constitutive equation for zero-shear viscosity of polymer melts. The central claim is that this identifies physically interpretable regimes, recovers local equations, and improves predictive accuracy over single global models or existing decision-tree approaches.

Significance. If the mixed-integer program reliably recovers the true regime partitions and equations, the framework would offer a practical, interpretable route to hybrid models for switching systems in chemical engineering, with direct relevance to modeling, optimization, and control. The basis-function parametrization for tractability and the concrete applications to dynamical systems and polymer rheology are strengths.

major comments (2)
  1. [Methods and Results sections (formulation and validation)] The central claim requires that the mixed-integer program recovers the underlying physical regime boundaries and equations (not merely fits the data). The manuscript supplies no synthetic-data experiments with known ground-truth partitions, no recovery guarantees, and no analysis of multiple optima with comparable training loss; without these, improved predictive accuracy does not establish correct regime identification.
  2. [Methods (optimization formulation)] § on the mixed-integer formulation: the claim that parametrizing splits and local models with basis functions produces a tractable problem whose global solution recovers the regimes is load-bearing, yet no details on the exact MINLP, solver behavior, or sensitivity to initialization are provided to support that the recovered partitions are the physically correct ones rather than alternative partitions with similar loss.
minor comments (1)
  1. [Abstract and Results] The abstract states accuracy gains but supplies no quantitative error metrics, cross-validation details, or comparison baselines; these should be added to the results section for reproducibility.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their constructive comments, which highlight important aspects of validating the method's ability to recover true regimes. We address each point below and will make revisions to strengthen the paper accordingly.

read point-by-point responses
  1. Referee: [Methods and Results sections (formulation and validation)] The central claim requires that the mixed-integer program recovers the underlying physical regime boundaries and equations (not merely fits the data). The manuscript supplies no synthetic-data experiments with known ground-truth partitions, no recovery guarantees, and no analysis of multiple optima with comparable training loss; without these, improved predictive accuracy does not establish correct regime identification.

    Authors: We agree that demonstrating recovery of known regimes on synthetic data would strengthen the central claim. The current manuscript focuses on real-world applications where the learned regimes are interpretable and align with physical understanding in hybrid systems and polymer rheology, and shows superior predictive accuracy. However, to directly address this, we will add synthetic experiments with ground-truth partitions in the revised version. We will also include an analysis of multiple local optima by reporting results from different initializations or solver settings to assess consistency of the recovered partitions. revision: yes

  2. Referee: [Methods (optimization formulation)] § on the mixed-integer formulation: the claim that parametrizing splits and local models with basis functions produces a tractable problem whose global solution recovers the regimes is load-bearing, yet no details on the exact MINLP, solver behavior, or sensitivity to initialization are provided to support that the recovered partitions are the physically correct ones rather than alternative partitions with similar loss.

    Authors: The manuscript presents the mixed-integer optimization formulation in the Methods section, where both splitting conditions and local models are parametrized with basis functions to enable tractability. We acknowledge that additional details on the specific MINLP structure, the solver employed, and empirical sensitivity to initialization would be beneficial. In the revision, we will expand this section to include the full mathematical formulation, solver information, and results from multiple optimization runs to demonstrate robustness and that the identified regimes are consistent rather than arbitrary alternatives with similar loss. revision: yes

Circularity Check

0 steps flagged

No circularity: standard optimization-based learning procedure

full rationale

The paper formulates symbolic decision trees as a mixed-integer program that parametrizes splitting conditions and local governing equations via basis functions, then solves for regime partitions and models from data. The claimed outputs (improved predictive accuracy and interpretable regimes) are the direct numerical results of this optimization rather than quantities defined by construction to equal the inputs. No self-citation chains, uniqueness theorems, or ansatzes are invoked in the provided abstract or description to justify core steps; the method is presented as an empirical discovery tool whose validity rests on solver performance and data fit, not on internal redefinition. This is a conventional data-driven modeling pipeline with no load-bearing reduction of predictions to fitted inputs.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Only the abstract is available, so specific free parameters, axioms, and invented entities cannot be extracted or verified from the full text.

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