SKG: A Law-Induced Engine from Inference to Induction
Abstract
This paper proposes the SKG (Symplectic-Kernel Gradient) reasoning engine for law-induced inference and induction. Laws are a priori; data provide instances. Inference is geometric evolution under law constraints. We organize symplectic geometry, GENERIC, kernel methods, RKHS, group-equivariant networks, and constrained mechanics into a unified, analyzable, implementable, verifiable framework. We propose the SKG octuple S = (M, g, omega, H, S, G, Delta, Pi), whose four components correspond to four levels of laws: conservation laws, constitutive relations, symmetry groups, and axiom systems. Main results: (1) Invariants enter metric construction via the Jacobian: g = J^T Sigma^-1 J + epsilon_G I. For constant cases, we establish inverse reconstruction theory: solvability rank condition (Thm 3.9), consistency criterion (Thm 3.11), and uniqueness theorem (Thm 3.14). (2) The kernel bandwidth matrix is uniquely determined by Fisher information and satisfies task-independence (Thm 3.19). (3) The metric reconstruction error decomposes into four terms (Thm 3.21), with squared condition number kappa(Sigma^*)^2 as the dominant amplification factor (Thm 3.22). (4) For state-dependent cases, we establish function-space reconstruction theory on matrix-valued RKHS (Thms 4.8, 4.9). (5) Three-layer projections handle axiom, symplectic-step, and conservation constraints. (6) The residual equation yields the observable formula, four-dimensional rank condition, and noise propagation, while g_qq is structurally unidentifiable. (7) Kernel parameterization yields the RKHS extrapolation bound (Thm 4.15) and strict OOD gain theorem in group directions (Thm 8.15). (8) The learning-decoupling theorem (Thm 9.1) proves the sole object of induction is the parameters of the task energy. Validation: 1D damped oscillator and 2D rotation-invariant system; 6 unit tests, 10 experiments (paired t-test, p < 0.01).
Figures & tables
| Law level | Mathematical object | SKG component | Task relevance |
|---|---|---|---|
| Symmetry group | Irrelevant | ||
| Axiom system | Irrelevant | ||
| Conservation laws | Irrelevant | ||
| Constitutive relations | Partially relevant |
| Aspect | Inference flow | Learning flow |
| Space | State space | Parameter space |
| Metric | (objective, task-independent) | (task-relevant) |
| Driving force | (energy gradient) | (loss gradient) |
| Dynamics | ||
| Learning object | None | (parameters of ) |
| Purpose | Reach target | Determine task energy |
| Dimension | PINN | SKG |
|---|---|---|
| Role of laws | Soft regularization | Hard structure |
| Violating laws | Tolerable (cost is loss) | Mathematically forbidden |
| OOD guarantee | None | RKHS bound |
| Constraint handling | Loss term | Three-layer projection |
| Equivariance | Data augmentation | Structural guarantee |
| Estimated part | All network parameters | Only parameters of |
| Component | Mathematical object | Law level | Function |
|---|---|---|---|
| Symplectic form | Conservation law | Geometry of conservative forces | |
| Scalar functions | Constitutive relation | Conservative quantity and dissipative drive | |
| Invariant map | Symmetry group | Physically important differences | |
| Projection operators | Axiom system | Allowed states |
| Status | Handling | |
|---|---|---|
| Numerically stable | Use least squares directly | |
| Regularization needed | Use ridge regression [ 51 , 50 ] | |
| Solution unreliable | Increase embeddings or reduce problem size |
| Condition | Recommended method |
|---|---|
| and small residual | Cholesky parameterization |
| and large residual | Switch to manifold optimization |
| Manifold optimization | |
| Cholesky parameterization + stochastic gradient |
| 1 | ||
|---|---|---|
| 10 | ||
| 100 |
| Question | Answer |
|---|---|
| How many samples are needed? | |
| What dominates the error? | Squared condition number |
| How to reduce the error? | Reduce condition number increase samples |
| When is transfer possible? | Metric is task-independent and distribution family matches |
| How to decouple? | Metric from Fisher, energy splits into objective and task |
| Level | Dependency | Origin |
|---|---|---|
| Embedding | Depends on | Jacobian of invariants with respect to state |
| Kernel bandwidth | Depends on | Covariance varies with position |
| Intrinsic metric | Depends on | Cholesky function or kernel expansion |
| Aspect | Constant | Function |
|---|---|---|
| Unknown | scalars | Infinite-dimensional function |
| Equation | Linear | Functional equation |
| Solution | Linear system | Function-space optimization |
| Solvability | Rank condition | Function-space rank condition |
| Basis function | Form | Suitable for |
|---|---|---|
| Gaussian kernel | Local variation | |
| Polynomial | Smooth variation | |
| Fourier | Periodic variation | |
| Neural network | General case |
| Operation | Complexity |
|---|---|
| evaluation | |
| computation | |
| computation | |
| Backpropagation |
| Projection | Symbol | Object | Constraint type |
|---|---|---|---|
| Axiom projection | State | Hard constraint | |
| Symplectic-step projection | Symplectic step | Degeneracy condition | |
| Conservation projection | State | Energy conservation |
| Operation | Kernel parameterization | MLP parameterization |
|---|---|---|
| Parameter count | ||
| Forward computation | ||
| Backpropagation | ||
| computation | ||
| Regularization | Analytic form | Requires autodiff |
| Aspect | Metric determination | Energy determination |
|---|---|---|
| Object | Parameters of | |
| Data | Domain data | Task data |
| Supervision | Unsupervised | Supervised |
| Task-relevant | No | Yes |
| Time | Offline | Online |
| Method | MLE + Fisher | Natural gradient flow |
| Aspect | Inference flow | Learning flow |
| Space | State space | Parameter space |
| Metric | (objective, task-independent) | (task-relevant) |
| Driving force | (energy gradient) | (loss gradient) |
| Dynamics | ||
| Learning object | None | (parameters of ) |
| Purpose | Reach target | Determine task energy |
| Object | Learned? | Task-relevant? |
|---|---|---|
| No | No | |
| No | Yes |
| Aspect | Standard ML | SKG learning flow |
|---|---|---|
| Metric | Learning object | Unsupervised determination |
| Estimated parameters | All network parameters | Parameters of |
| Training cost | Related to all parameters | Only related to |
| Transferability | Requires domain adaptation | Metric naturally transferable |
| Energy decomposition | None |
| Bayesian inference | SKG | Meaning |
|---|---|---|
| Prior | Metric | Knowledge before the task |
| Likelihood | Energy | Requirement of task data |
| Posterior | Learned | Induction after the task |
| Statistical physics | SKG | Meaning |
|---|---|---|
| Inertial mass | Metric | Physical property, not a learning object |
| Hamiltonian | Energy | System dynamics |
| Temperature | Learning rate | External parameter |
| Free energy | Loss | Optimization objective |
| Question | Answer |
|---|---|
| Is the metric learned? | No, objectively determined by Fisher |
| What is the learning object? | Parameters of |
| Is learned? | No, but task-relevant; estimated once |
| When is the metric determined? | Offline, before the task begins |
| How to transfer? | Share within the same domain |
| Training cost? | Only related to the parameter count of |
| Item | Setting |
|---|---|
| Training domain (1D) | , trajectories, 500 steps each |
| OOD domain (1D) | , , 200 test points |
| Training domain (2D) | , |
| OOD domain (2D) | (pure rotation), (radius extrapolation) |
| Quantity | Value |
|---|---|
| True | 1.5 |
| Mean observed | 1.5000000000 |
| Maximum error |
| Quantity | Value |
|---|---|
| shape | |
| 7 |
| Residual | |
|---|---|
| Non-diagonal |
| Quantity | Value |
|---|---|
| Expected | |
| Numerical | |
| Maximum error |
| Theoretical | Measured | |
|---|---|---|
| 0.05 | 2.000 | 2.001 |
| 0.10 | 1.000 | 1.002 |
| 0.20 | 0.500 | 0.500 |
| 0.50 | 0.200 | 0.200 |
| 1.00 | 0.100 | 0.100 |
| 2.00 | 0.050 | 0.050 |
| Quantity | Value |
| Maximum error between and numerical Hessian |
| Model | Structure | Parameter count |
|---|---|---|
| SKG | 1153 | |
| Black-box | 1129 |
| Model | OOD MSE | Standard deviation |
|---|---|---|
| SKG | ||
| Black-box | ||
| Ratio | — |
| Model | Parameterization | Parameter count |
|---|---|---|
| Kernel | 59 | |
| MLP | 61 |
| Model | OOD MSE | Standard deviation |
|---|---|---|
| Kernel | ||
| MLP | ||
| Ratio | — |
| Quantity | Value |
|---|---|
| Mean | |
| Mean | |
| Mean | |
| Mean bound | |
| Tightness ratio |
| Method | Structure | learning | learning |
|---|---|---|---|
| Joint | Simultaneous optimization of and | MLP | MLP |
| Independent | Two-stage | MLP (small ) | Constant |
| Method | OOD MSE | Standard deviation | RMSE relative error |
|---|---|---|---|
| Joint | |||
| Independent | |||
| Ratio | — | — |
| Steps | Model | ID MSE | OOD MSE | OOD/ID ratio |
|---|---|---|---|---|
| 1,000 | K | |||
| 1,000 | M | |||
| 3,000 | K | |||
| 3,000 | M | |||
| 10,000 | K | |||
| 10,000 | M |
| Check | Threshold | Result | Judgment |
| K’s OOD/ID ratio | – | PASS | |
| M’s OOD/ID ratio | – | PASS | |
| Yes | PASS | ||
| M ratio K ratio | Yes | – times | PASS |
| Lower bound holds | Yes | 0 violations | PASS |
| Lower bound meaningful | Yes | Trivial |
| Rotation angle | Error |
|---|---|
| 0.3 rad | |
| 0.7 rad | |
| 1.2 rad |
| Model | Intrinsic metric |
|---|---|
| Const | constant (Chapter 3 model) |
| Func | learned by MLP (Chapter 4 model) |
| MLP | Unstructured MLP control |
| Model | OOD MSE | Relative to Func |
|---|---|---|
| Const | ||
| Func | — | |
| MLP |
| Metric | Func | Const | Ratio |
|---|---|---|---|
| Interpolation error | |||
| Extrapolation error |
| Seed | bound | ratio | ||
|---|---|---|---|---|
| 0 | ||||
| 1 | ||||
| 2 |
| Seed | SKG learning flow (1 parameter) | Standard MLP (1185 parameters) |
|---|---|---|
| 0 | ||
| 1 | ||
| 2 | ||
| 3 | ||
| 4 |
| Method | Parameter count | OOD MSE (mean std) |
|---|---|---|
| SKG learning flow | 1 | |
| Standard MLP | 1185 | |
| Ratio |
| Experiment | Validation target | Result | Key value |
|---|---|---|---|
| T1 | Proposition 6.3 1D observable | PASS | Error |
| T2 | Proposition 6.4 4D rank condition | PASS | |
| T3 | Proposition 6.6 unidentifiable | PASS | Residual independent of |
| T4 | Proposition 6.7 Potential–metric coupling | PASS | Error |
| T5 | Proposition 6.5 Noise propagation | PASS | Max error |
| T6 | Theorem 3.4 Kernel Hessian metric | PASS | Error |
| Dimension | Existing methods | SKG |
|---|---|---|
| Role of laws | Soft regularization or architectural constraint | Hard structure |
| Violating laws | Tolerable (cost is loss) | Mathematically forbidden |
| OOD guarantee | None or partial | RKHS bound |
| Constraint handling | Loss term or architecture design | Three-layer projection |
| Equivariance | Data augmentation or architecture design | Structural guarantee |
| Learning object | All network parameters | Only parameters of |
| SKG component | General form | Application examples |
|---|---|---|
| Symplectic structure | Known conservation law | Mechanics, electromagnetism, quantum mechanics [ 16 , 18 ] |
| Energy | Known constitutive relation | Material models, potential functions |
| Invariants | Symmetry group representation | Rotation, translation, scale, permutation |
| Projections | Constraint handling | Hard constraints, conservation laws, gauge fixing [ 31 , 32 ] |
| Estimated metric | Unknown dissipation/source | Damping, friction, diffusion |
| Intrinsic metric | Coordinate-free form of | Transfer learning, OOD distance |
Appendix figures & tables3 assets
Supplementary material from the paper’s appendix.
Appendix
| Order | Expression | Geometric quantity |
|---|---|---|
| 0 | Kernel value | |
| 2 | Covariant metric | |
| 3 | Even function, zero | |
| 4 | Seed of curvature |
| Operation | Complexity |
|---|---|
| (number of components) |
| Concept | Existing literature | SKG’s advance |
|---|---|---|
| Kernel to metric | Standard Hessian metric [ 23 , 24 ] | Systematized for inference |
| Connection and curvature | Riemannian geometry standard [ 22 , 21 ] | Related to kernel higher-order derivatives |
| Curvature of Hessian metrics | Information geometry [ 23 , 24 ] | Applied to OOD analysis |
| Curvature and generalization | Partial work | Heuristic connection, unproven |
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