Finite-step statistical mechanics of scale-invariant learning: spectral equations of state and curvature transport
Organizations: Radboud University, Nijmegen, The Netherlands · Independent researcher, Hamburg, Germany
Abstract
Stationary learning admits an ideal-gas description under restrictive noise assumptions. In neural networks whose gradient noise departs from these assumptions, however, an entropy-scaling relation resembling a Maxwell relation remains approximately valid. We ask which thermodynamic-looking relations follow from scale symmetry rather than equilibrium, and how departures from the ideal-gas description can be quantified, for discrete stochastic gradient dynamics with memory. An exact rescaling of trajectories explains the entropy relation without assuming thermal equilibrium. Within a local harmonic approximation, self-adjusting weight norms yield a spectral equation of state whose virial coefficients are set by moments of the curvature spectrum, and coupled parameter groups can sustain stationary probability currents. Our central result beyond this approximation is an exact curvature-transport identity. Together with a finite-step loss balance, it decomposes corrections to the harmonic fluctuation relation into measurable curvature changes, finite-step remainders, gradient-memory correlations and finite-window drift terms. A related displacement-weighted curvature change provides a diagnostic of the arrow of time; its mean and second moment give a lower bound on the relative entropy between forward and reversed state pairs. We also calculate the activation-boundary contribution to curvature for rectified teacher-student networks with Gaussian inputs. Tests in sphere models, teacher-student networks and convolutional networks on CIFAR-10 and CIFAR-100 support the transport description and identify limits of the harmonic and cubic-remainder approximations. These results separate symmetry-based relations from equilibrium assumptions and provide quantitative diagnostics of nonideal fluctuations in learning dynamics.
Figures & tables
| learning rate, weight decay, decay per step | mean-gradient power | ||
| memory parameter, ( 3 ) | curvature along | ||
| stability threshold of | noise power | ||
| ; | parameters; norm and direction of group | noise curvature | |
| angular step | update curvature | ||
| curvature and angular noise of mode | , | its linear value, ratio | |
| edge ratio | linear-FDR ratio, ( 15 ) |
| continuum | linear FDR | stiff var/pred | soft var/pred | |||
|---|---|---|---|---|---|---|
| 0.30 | 0.142 | 1.157 | 1.000 | 0.997 (1.091) | ||
| 0.10 | 0.307 | 1.419 | 0.999 | 0.999 (1.042) | ||
| 0.10 | 0.389 | 1.598 | 1.002 | 1.011 (1.114) | ||
| 0.30 | 0.316 | 1.431 | 1.004 | 1.034 (1.466) | ||
| 0.10 | 0.447 | 1.743 | 1.008 | 1.044 (1.351) | ||
| 0.30 | 0.399 | 1.595 | 1.015 | 1.106 (2.188) |
| SGD | EMA momentum | AdamW | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| SDE | Edge | SDE | SDE | |||||||
| – | 1.08 | 17% | 0.89 | 0.28 | 0.97 | 0.95 | 0.02 | 0.90 | 0.89 | 0.03 |
| – | 1.15 | 23% | 0.88 | 0.49 | 0.89 | 0.88 | 0.03 | 0.87 | 0.86 | 0.04 |
| – | 1.16 | 26% | 0.82 | 0.54 | 0.78 | 0.76 | 0.04 | 0.76 | 0.75 | 0.05 |
| 1.35 | 36% | 0.80 | 0.79 | 0.74 | 0.72 | 0.07 | 0.72 | 0.71 | 0.06 | |
| – | 1.50 | 50% | 0.64 | 1.22 | 0.64 | 0.61 | 0.13 | 0.63 | 0.61 | 0.13 |
| modes | var/theory, median | mean s.e. | var/continuum, median | |
|---|---|---|---|---|
| 46 | 1.07 | 1.32 | ||
| 47 | 0.98 | 1.68 | ||
| 24 | 0.82 | 1.96 | ||
| 11 | 0.50 | 2.39 |
| model | activation | flips | test acc. | |||||||
| thin | ReLU | 0.858 | 0.914 | 0.36 | 1.3% | – | 0.678 | |||
| Softplus 0.5 | 0.909 | 0.959 | 0.31 | 1.5% | 0.11 | 0.714 | ||||
| Softplus 0.05 | 0.963 | 0.971 | 0.31 | 1.4% | 1.02 | 0.680 | ||||
| ReLU | 0.881 | 0.895 | 0.48 | 2.1% | – | 0.706 | ||||
| Softplus 0.5 | 0.929 | 0.952 | 0.37 | 2.5% | 0.17 | 0.731 | ||||
| Softplus 0.05 | 1.017 | 0.977 | 0.33 | 2.4% | 1.71 | 0.703 |
| setting, | residual | gap | ||||||
|---|---|---|---|---|---|---|---|---|
| CIFAR-10 | ||||||||
| thin ReLU | ||||||||
| thin ReLU | ||||||||
| thin Softpl. | ||||||||
| thin Softpl. | ||||||||
| pract. ReLU | ||||||||
| Statement | Level | Evidence |
|---|---|---|
| Norm balance per invariant group ( Proposition 1 ) | exact (invariant group) | networks: median 1.004; per group 1.000 |
| Scaling symmetry, entropy relation ( Proposition 2 , Corollary 3 ) | exact (invariant groups; trained head at fixed hyperparameters) | sphere 4.000/16.007; networks 0.8–4.3%; trained head |
| Loss balance, finite-decay identity ( Proposition 4 , Theorem 5 ) | exact (any network; common for Theorem 5 ) | SGD networks: RMS 0.038 (20 runs); EMA networks, window form: , 12.5 (12 runs each); teacher–student (24 runs); trained head – |
| Curvature transport, arrow of time ( Propositions 6 and 7 ) | exact (any network; common ) | teacher–student: within 0.16%, at 13–277 s.e.; EMA networks: accounting , 21 (12 runs each), resolved in 16 of 22 runs |
| Activation-boundary remainder ( Lemma 14 ) | asymptotic (small steps, smooth pre-activation density) | thin ResNet profiles (all but one small, non-monotone Softplus profile) |
| Singular curvature of ReLU committees ( Proposition 15 ) | exact (Gaussian inputs) | fixed states within ; teacher–student vs |
Appendix figures & tables2 assets
Supplementary material from the paper’s appendix.
Appendix
| noise | /rhs ( 18 ) | ( 16 ) | ( 41 ) | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Gaussian | 0.3 | 0.10 | 1.0003 | 1.0002 | 1.0002 | 1.99 | 1.0037 | ||
| 0.76 | 1.0015 | 0.9998 | 1.0017 | 1.99 | 1.0292 | ||||
| 2.00 | 1.0042 | 0.9997 | 1.0045 | 1.99 | 1.0825 | ||||
| 4.00 | 1.0095 | 1.0001 | 1.0094 | 1.98 | 1.1886 | ||||
| Gaussian | 0 | 0.76 | 1.0025 | 0.9999 | 1.0026 | 2.00 | 1.0774 | ||
| 4.00 | 1.0144 | 1.0001 | 1.0143 | 2.00 | 1.6641 |
| noise | /( 15 ) | ratio | pred. | mem. (%) | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 0.5 | G | 0.9996 | 1.0040 | 0.9997/0.9998 | 0.9999 | 1.0045 | 1.0044 | +0.10 | 0.1/0.1 (0.1) | |
| nG | 0.9974 | 1.0017 | 0.9977/1.0005 | 1.0043 | 1.0015 | -0.05 | 0.1/0.2 (0.1) | |||
| 0.5 | G | 0.9989 | 1.0202 | 1.0001/1.0001 | 0.9990 | 1.0213 | 1.0217 | +0.30 | 1.3/1.5 (1.3) | |
| nG | 0.9974 | 1.0153 | 0.9990/1.0002 | 1.0180 | 1.0175 | +0.10 | 1.4/1.5 (1.3) | |||
| 0.9 | G | 0.9987 | 1.0027 | 0.9994/1.0009 | 0.9991 | 1.0040 | 1.0035 | +0.30 | 1.0/1.0 (0.9) | |
| nG | 0.9963 | 1.0000 | 0.9983/0.9999 | 1.0037 | 1.0015 | +0.12 | 1.0/1.0 (0.9) |
Statistical Physics of Learning
Statistical physics of learning uses tools from physics to explain how data, model structure, and training dynamics shape learning and generalization.
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