Despite its huge number of variants, standard Low-Rank Adaptation (LoRA) is still a dominant technique for parameter-efficient fine-tuning (PEFT). Nonetheless, it faces persistent challenges, including the pre-selection of an optimal rank and rank-specific hyper-parameters, as well as the deployment complexity of heterogeneous-rank modules and more sophisticated LoRA derivatives. In this work, we introduce LoRA-Squeeze, a simple and efficient methodology that aims to improve standard LoRA learning by changing LoRA module ranks either post-hoc or dynamically during training}. Our approach posits that it is better to first learn an expressive, higher-rank solution and then compress it, rather than learning a constrained, low-rank solution directly. The method involves fine-tuning with a deliberately high(er) source rank, reconstructing or efficiently approximating the reconstruction of the full weight update matrix, and then using Randomized Singular Value Decomposition (RSVD) to create a new, compressed LoRA module at a lower target rank. Extensive experiments across 13 text and 10 vision-language tasks show that post-hoc compression often produces lower-rank adapters that outperform those trained directly at the target rank, especially if a small number of fine-tuning steps at the target rank is allowed. Moreover, a gradual, in-tuning rank annealing variant of LoRA-Squeeze consistently achieves the best LoRA size-performance trade-off.

翻译：尽管存在大量变体，标准的低秩自适应（LoRA）仍然是参数高效微调（PEFT）的主导技术。然而，它仍面临持续存在的挑战，包括最优秩及秩特定超参数的预选、异构秩模块的部署复杂性以及更复杂的LoRA衍生方法。本文提出LoRA-Squeeze，这是一种通过在训练后或训练期间动态调整LoRA模块秩来改进标准LoRA学习的简单高效方法。我们的方法主张，首先学习一个表达能力更强的高秩解再进行压缩，优于直接学习受约束的低秩解。该方法包括：使用刻意设定的较高源秩进行微调，重构或高效近似重构完整的权重更新矩阵，然后利用随机奇异值分解（RSVD）创建一个新的、压缩至更低目标秩的LoRA模块。在13项文本任务和10项视觉语言任务上的大量实验表明，后验压缩通常能产生比直接在目标秩上训练效果更优的低秩适配器，尤其是在允许少量目标秩微调步骤的情况下。此外，LoRA-Squeeze的一种渐进式动态秩退火变体始终能实现最佳的LoRA尺寸与性能权衡。