Frozen Factor or Spectral Band? Disentangling Two Choices in Low-Rank LoRA
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Abstract (arXiv)
Spectral variants of low-rank adaptation (LoRA) choose both a subspace and which factor to freeze. We separate these choices by freezing the input factor A or output factor B on the top or bottom singular directions of pretrained weights, with learning rates selected separately. At rank 2, the same-band advantage of freezing A is larger than either within-factor band difference on all four task-model pairs with complete comparisons. Freezing B also trails comparable-budget free LoRA by 8-18 percentage points on five pairs spanning a formatting task and OpenBookQA. The A-frozen advantage persists in a single-GPU-model replication and within individual MLP module groups, including controls with equal or greater trainable counts for B frozen, and when A is frozen on a random orthonormal basis. The factor contrast weakens with rank. On OpenBookQA / Qwen2.5-1.5B at rank 16, PEFT's MiCA implementation trails comparable-budget LoRA by 3.08 points under a shared training recipe transferred from the MiCA paper. A trained oracle output subspace largely removes the low-rank deficit; partial warm-up gains recur across three direction seeds. The factor-versus-band ordering is descriptive; an approximate multiplicity audit weakens several earlier significance claims. These results extend known factor asymmetry by showing how its magnitude depends on spectral placement, rank and training conditions.
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References · 30
- 2024The Llama 3 Herd of Modelscited by 14,715
- 2021LoRA: Low-Rank Adaptation of Large Language Modelscited by 14,380
- 2024Qwen2.5 Technical Reportcited by 4,942
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- 2023Mistral 7Bcited by 3,164
- 2017Decoupled Weight Decay Regularizationcited by 1,831
- 2024GaLore: Memory-Efficient LLM Training by Gradient Low-Rank Projectioncited by 463
- 2024LoRA+: Efficient Low Rank Adaptation of Large Modelscited by 377
- 2023VeRA: Vector-based Random Matrix Adaptationcited by 300
- 2024PiSSA: Principal Singular Values and Singular Vectors Adaptation of Large Language Modelscited by 269
- 2024LoRA-GA: Low-Rank Adaptation with Gradient Approximationcited by 141
18 more
- 2023LoRA-FA: Efficient and Effective Low Rank Representation Fine-tuningcited by 137
- 2024Flora: Low-Rank Adapters Are Secretly Gradient Compressorscited by 108
- 2024MiLoRA: Harnessing Minor Singular Components for Parameter-Efficient LLM Finetuningcited by 94
- 2024Asymmetry in Low-Rank Adapters of Foundation Modelscited by 86
- 2024LoRA-XS: Low-Rank Adaptation with Extremely Small Number of Parameterscited by 76
- 2024SVFT: Parameter-Efficient Fine-Tuning with Singular Vectorscited by 58
- 2024The Impact of Initialization on LoRA Finetuning Dynamicscited by 54
- 2024CorDA: Context-Oriented Decomposition Adaptation of Large Language Models for Task-Aware Parameter-Efficient Fine-tuningcited by 44
- 2025LoRA-One: One-Step Full Gradient Could Suffice for Fine-Tuning Large Language Models, Provably and Efficientlycited by 38
- 2024Initialization using Update Approximation is a Silver Bullet for Extremely Efficient Low-Rank Fine-Tuningcited by 22
- 2024Parameter Efficient Fine-tuning via Explained Variance Adaptationcited by 20
- 2025Sharp Generalization Bounds for Foundation Models with Asymmetric Randomized Low-Rank Adapterscited by 11
- 2025PiCa: Parameter-Efficient Fine-Tuning with Column Space Projectioncited by 6
- 2025SSVD: Structured SVD for Parameter-Efficient Fine-Tuning and Benchmarking under Domain Shift in ASRcited by 4
- 2026Beware of the Batch Size: Hyperparameter Bias in Evaluating LoRAcited by 4
- 2026Least but not Last: Fine-tuning Intermediate Principal Components for Better Performance-Forgetting Trade-Offscited by 2
- 2026MiCA Learns More Knowledge Than LoRA and Full Fine-Tuningcited by 1
- 2026Bilinear Optimization Divergence: Diagnosing Factor-Constrained LoRA Continual Learningcited by 1
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