About alpha/rank in lora

[Vital1162]

How does $\alpha$ in Lora affect performance in training?
I usually see everyone set to $2r$. But why?
About the rank, I always set it to 128-256 if the dataset quantity is good.

[Erland366]

I think because in LoRA, you use alpha for the learning rate of the LoRA, which is defined by

$$ LR_{LoRA} = \frac{\alpha}{\sqrt{r}} \times LR $$

But in finetuning, you might want to aggresively update the adapter since your data is usually fewer than pretrain.

Probably my intuition is as long as the result of $\frac{\alpha}{\sqrt{r}}$ is more than one then you good to go

[Vital1162]

thank you for your response @Erland366, but does dataset size affect these parameters?

[Erland366]

I've heard in the Discord that if you have smaller dataset, then use smaller rank and alpha. But I haven't tested this a lot myself