Parameter-efficient fine-tuning (PEFT) is a popular method for tailoring pre-trained large language models (LLMs), especially as the models' scale and the diversity of tasks increase. Low-rank adaptation (LoRA) is based on the idea that the adaptation process is intrinsically low-dimensional, i.e., significant model changes can be represented with relatively few parameters. However, decreasing the rank encounters challenges with generalization errors for specific tasks when compared to full-parameter fine-tuning. We present MELoRA, a mini-ensemble low-rank adapters that uses fewer trainable parameters while maintaining a higher rank, thereby offering improved performance potential. The core idea is to freeze original pretrained weights and train a group of mini LoRAs with only a small number of parameters. This can capture a significant degree of diversity among mini LoRAs, thus promoting better generalization ability. We conduct a theoretical analysis and empirical studies on various NLP tasks. Our experimental results show that, compared to LoRA, MELoRA achieves better performance with 8 times fewer trainable parameters on natural language understanding tasks and 36 times fewer trainable parameters on instruction following tasks, which demonstrates the effectiveness of MELoRA.

MELoRA是一种采用较少可训练参数但保持较高秩的迷你低秩适配器，用于针对预训练大型语言模型进行性能优化的方法。实验证明，在自然语言理解和指令跟随任务上，相较于低秩适配器LoRA，MELoRA在拥有8倍较少可训练参数时表现更好，而在指令跟随任务上拥有36倍较少可训练参数时也表现更好，证明了MELoRA的有效性。

用于参数高效微调的Mini-Ensemble低秩适配器