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Temperature is All You Need for Generalization in Langevin Dynamics and other Markov Processes
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Shows that any Markov training process with a Gibbs-style stationary distribution has a generalization gap bound, at any time, of order sqrt((beta E L(theta_0) + ln(1/delta))/N), via a second-law divergence bound; applied to Langevin dynamics.
Problem
Generalization gap of over-parameterized models trained with stochastic Markov training dynamics (e.g., Langevin dynamics), where existing bounds depend on training time, mixing, dimensionality, or gradient statistics.
Approach
Bounds the KL and Rényi-infinity divergence of the marginal distribution at any time from a data-independent base measure using a generalized second law (data processing monotonicity relative to a Gibbs stationary distribution), then plugs into PAC-Bayes bounds. The symmetric divergence of a Gibbs distribution removes the partition function, so no mixing, spectral gap or time dependence is needed.
Key results
- For regularized or bounded Langevin dynamics with p_0 matching the stationary base measure, the generalization gap at any time is bounded by sqrt((beta E L(theta_0)+ln(N/delta))/(2N)) with no dependence on training time or dimension.
- Inverse temperature beta = O(N) can be tuned to give non-vacuous bounds (bound plus training error below 0.5) on small binary classification tasks with overparameterized networks.
- In linear regression with CLD, the bound is useful for d << beta << N, giving a vanishing gap since E_{p0}L=O(1).
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Add positive-temperature noise to the training dynamics | Langevin dynamics · Generalization gap (any training time) | generalization gap | Helped |
Surprising findings
- Generalization guarantees hold at every time step without mixing, and the bound does not depend on dimension, gradient norms or training time.
- Symmetrized divergence removes the partition function from the analysis, and the bound is insensitive to whether training converged.
Limitations
- Requires regularization or bounded domain matching the initialization; unregularized training with stationary probability measures is not covered.
- Requires beta = O(N) for non-vacuous bounds, and discrete-time SGD needs an explicit stationary distribution or Metropolis correction.
- Only the generalization gap is bounded, not the absolute error; bound is not very tight at noise levels allowing non-vacuous results.
Experimental setup
Datasets: binary MNIST Fashion MNIST SVHN parity problem synthetic linear regression
Benchmarks: binary MNIST Fashion MNIST SVHN parity problem
Metrics: generalization gap bound training error sum of bound and training error
Baselines: Chen et al. CLD stability bound Farghly et al. bounds for CLD Li et al. SGLD bound Raginsky et al. Gibbs-based bounds
Builds on: PAC-Bayes bounds Langevin dynamics Cover's second law / data processing inequality
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