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Why Warmup the Learning Rate? Underlying Mechanisms and Improvements

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arxiv 2406.09405 v2 pith:KNA3GHAN submitted 2024-06-13 cs.LG cond-mat.dis-nnstat.ML

Why Warmup the Learning Rate? Underlying Mechanisms and Improvements

classification cs.LG cond-mat.dis-nnstat.ML
keywords warmuptextlearningtrgtadaminitinitializationlarger
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved
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It is common in deep learning to warm up the learning rate $\eta$, often by a linear schedule between $\eta_{\text{init}} = 0$ and a predetermined target $\eta_{\text{trgt}}$. In this paper, we show through systematic experiments using SGD and Adam that the overwhelming benefit of warmup arises from allowing the network to tolerate larger $\eta_{\text{trgt}}$ {by forcing the network to more well-conditioned areas of the loss landscape}. The ability to handle larger $\eta_{\text{trgt}}$ makes hyperparameter tuning more robust while improving the final performance. We uncover different regimes of operation during the warmup period, depending on whether training starts off in a progressive sharpening or sharpness reduction phase, which in turn depends on the initialization and parameterization. Using these insights, we show how $\eta_{\text{init}}$ can be properly chosen by utilizing the loss catapult mechanism, which saves on the number of warmup steps, in some cases completely eliminating the need for warmup. We also suggest an initialization for the variance in Adam which provides benefits similar to warmup.

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Cited by 4 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. Directional Curvature from Armijo Backtracking: A Low-Cost Sharpness Probe and a Calibration-Free Learning-Rate Safeguard for Adam

    cs.LG 2026-07 conditional novelty 6.0

    Armijo backtracking brackets directional curvature and tracks top Hessian eigenvalue; one init probe with fixed κ=2 along Adam's direction prevents Adam divergence across wide learning-rate grids.

  2. Directional Curvature from Armijo Backtracking: A Low-Cost Sharpness Probe and a Calibration-Free Learning-Rate Safeguard for Adam

    cs.LG 2026-07 conditional novelty 6.0

    Armijo backtracking brackets directional curvature and, used once along Adam's update direction with fixed κ=2, prevents Adam divergence from over-large initial learning rates at ~1% cost.

  3. Scale Weight Decay and Train Better

    cs.LG 2026-07 conditional novelty 5.0

    Muon with weight decay scaled by η/η_max reaches the same MoE validation loss ~30% faster than constant-decay Muon while preserving asymptotic stationarity of the unregularized objective.

  4. Directional Curvature from Armijo Backtracking: A Low-Cost Sharpness Probe and a Calibration-Free Learning-Rate Safeguard for Adam

    cs.LG 2026-07 conditional novelty 5.0

    A single Armijo backtracking line search at initialization estimates local Hessian sharpness and caps Adam's learning rate to prevent divergence, with fixed safety factor κ=2 across nine architectures.