arXiv Machine Learning

Are Parameter-Efficient Fine-tuning Methods Really Different?

The paper investigates whether different parameter‑efficient fine‑tuning (PEFT) methods truly differ in their approach and impact. By comparing six methods on language and diffusion models, the authors find that many LoRA‑family techniques approximately preserve pretrained geometry, and that restoring slightly drifted singular‑value spectra largely maintains task performance, challenging the need for explicit geometric preservation. They also observe distinct adaptation–retention trade‑offs: LoRA limits forgetting best, DoRA scores higher on average, and PiSSA incurs more retention costs, with performance gains linked to modifications in specific spectral components.

arXiv Machine Learning
Oct 5

MuLoRA: Spectrally Balanced Low-Rank Adaptation for Continual Learning

MuLoRA introduces a spectrally balanced low‑rank adaptation method for continual learning, addressing the issue of spectral plasticity collapse where adaptation energy concentrates in few singular modes. It uses historical whitening to identify task‑adaptive input directions and approximate polar orthogonalization of momentum updates to reduce spectral concentration, ensuring effective utilization of the low‑rank space. Experiments on five class‑incremental benchmarks and eight incremental settings show MuLoRA achieving the highest mean accuracy in 15 of 16 metrics.

By Junkang Liu
arXiv Machine Learning
Sep 14

Rank-Efficient LoRA via Joint Tangent-Space Optimization under Isotropic Curvature

The paper introduces ISO-LoRA, an optimizer that improves rank utilization in Low‑Rank Adaptation (LoRA) by coupling factor updates through spectral descent on the induced tangent perturbation in weight space. Experiments on GPT‑2 adaptation show that standard optimizers like AdamW concentrate updates in a few singular directions, whereas ISO-LoRA distributes energy more evenly, leading to higher effective rank and better downstream performance across 0.1B‑7B models. The authors provide theoretical guarantees under a stylized spiked‑gradient model and demonstrate that ISO-LoRA consistently outperforms factor‑wise optimizers, especially at moderate‑to‑large LoRA ranks.

By Zihan Zhu, Zhehang Du, Xuyang Chen, Tim Tsz-Kit Lau, Jiayuan Wu, X. Y. Han, Qi Long, Weijie Su