Gradient Descent Happens in a Tiny Subspace
Not on the map. Why?
Abstract (arXiv)
We show that in a variety of large-scale deep learning scenarios the gradient dynamically converges to a very small subspace after a short period of training. The subspace is spanned by a few top eigenvectors of the Hessian (equal to the number of classes in the dataset), and is mostly preserved over long periods of training. A simple argument then suggests that gradient descent may happen mostly in this subspace. We give an example of this effect in a solvable model of classification, and we comment on possible implications for optimization and learning.
Key facts. Cited by 217 papers in the map (data through 14 Oct 2026). First posted on arXiv 12 Dec 2018.
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Citing papers per year: 2020: 1; 2021: 29; 2022: 29; 2023: 23; 2024: 41; 2025: 25; 2026: 69.
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- 2022Memorization Without Overfitting: Analyzing the Training Dynamics of Large Language Modelscited by 220
- 2021Fishr: Invariant Gradient Variances for Out-of-Distribution Generalizationcited by 186
- 2024LoRA-GA: Low-Rank Adaptation with Gradient Approximationcited by 141
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- 2021Large Scale Private Learning via Low-rank Reparametrizationcited by 88
- 2021Do Not Let Privacy Overbill Utility: Gradient Embedding Perturbation for Private Learningcited by 86
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- 2025ASGO: Adaptive Structured Gradient Optimizationcited by 57
- 2022Stop Wasting My Time! Saving Days of ImageNet and BERT Training with Latest Weight Averagingcited by 54
- 2021Analytic Insights into Structure and Rank of Neural Network Hessian Mapscited by 52
12 most cited of 203 All 203 (JSON)
- 2026A Refresh Interval Does Not Fully Specify a Refresh Schedule: Learning-Rate-Dependent Placement in Kronecker-Preconditioned Language Model Training13 Oct 2026
- 2026Scalable AI Uncertainty Quantification via Generalized Laplace Active Subspaces8 Oct 2026
- 2026Eigenvalues of the Hessian in Deep Learning: The Origin of Symmetry and Its Breaking7 Oct 2026
- 2026Task-Oriented Rank Adaptation for Continual Learning in Text Classification1 Oct 2026
- 2026Traversing the solution space of neural networks with Hessian Null Space Continuation29 Sep 2026
- 2026Neural Succession: A Mesoscopic Theory of Invasion, Coexistence, and Stabilization in Continual Learning28 Sep 2026
- 2026Early Learning Shapes Later Directions Of Representation Change In Continual Learning28 Sep 2026
- 2026AIM-ZO: Activation-Informed Subspace Maintenance for Zeroth-Order LLM Fine-Tuning28 Sep 2026
- 2026Understanding the Subspace Stabilization of the Hessian and Gradient Covariance Matrix25 Sep 2026
- 2026Communication-Efficient LLM Adaptation over Decentralized GPU Meshes13 Sep 2026
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- 2026The Multiple Timescales of Gradient Descent on the Edge of Stability: A Perturbative Derivation of the Central Flow1 Sep 2026
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