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arXiv 2602.01522cs.LGcs.CV
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何时秩-1足够?基于几何的初始化方法用于参数高效微调

When Is Rank-1 Enough? Geometry-Guided Initialization for Parameter-Efficient Fine-Tuning

School of Computing and Information Systems, University of Melbourne, Melbourne, Australia(计算机与信息系统学院,墨尔本大学,墨尔本,澳大利亚)

Haoran Zhao, Soyeon Caren Han, Eduard Hovy

AI总结:

本文提出Gap-Init方法,通过几何感知初始化稳定秩-1 LoRA微调,证明初始对齐对训练稳定性的重要性。

摘要:

参数高效微调(PEFT)是适应多模态大语言模型的标准方法,但极低秩设置——尤其是秩-1 LoRA——往往不稳定。我们表明,这种不稳定性不仅仅是因为容量有限:在秩-1范围内,优化对更新方向高度敏感。具体来说,预训练的视觉和文本特征形成不匹配的各向异性区域,产生一个主导的'间隙'方向,其作用如同翻译成分,并在秩-1约束下不成比例地引导早期梯度。分析预训练表示,我们识别出一个主导早期梯度流动的模态间隙轴,而随机的秩-1初始化不太可能与之对齐,导致梯度弱和训练崩溃。我们提出了Gap-Init,一种基于几何的初始化方法,它将秩-1 LoRA方向与从小校准集估计的模态间隙向量对齐,同时保持初始LoRA更新为零。在多个视觉-语言任务和主干网络上,Gap-Init一致地稳定了秩-1训练,并能匹配或优于强秩-8基线。我们的结果表明,在极低秩极限下,初始对齐可能与秩本身同样重要。

英文摘要:

Parameter-efficient fine-tuning (PEFT) is a standard way to adapt multimodal large language models, yet extremely low-rank settings -- especially rank-1 LoRA -- are often unstable. We show that this instability is not solely due to limited capacity: in the rank-1 regime, optimization is highly sensitive to the update direction. Concretely, pretrained vision and text features form mismatched anisotropic regions, yielding a dominant "gap" direction that acts like a translation component and disproportionately steers early gradients under rank-1 constraints. Analyzing pretrained representations, we identify a modality-gap axis that dominates early gradient flow, while a random rank-1 initialization is unlikely to align with it, leading to weak gradients and training collapse. We propose Gap-Init, a geometry-aware initialization that aligns the rank-1 LoRA direction with an estimated modality-gap vector from a small calibration set, while keeping the initial LoRA update zero. Across multiple vision-language tasks and backbones, Gap-Init consistently stabilizes rank-1 training and can match or outperform strong rank-8 baselines. Our results suggest that at the extreme low-rank limit, initial alignment can matter as much as rank itself.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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