LoRA Methods in Large Language Models
LoRA Methods in Large Language Models Low-Rank Adaptation (LoRA) methods fine-tune large models by learning low-rank decompositions of weight updates, achieving full fine-tuning performance with fraction of trainable parameters. The engineering challenge involves selecting optimal ranks for different layers, managing multiple LoRA adaptations simultaneously, merging adaptations efficiently, scaling to extremely large models, and maintaining training stability while maximizing parameter efficiency. LoRA Methods in Large Language Models Explained for Beginners - LoRA methods are like adding thin transparent overlays to a printed map instead of reprinting the entire map - you place a clear sheet with just the new roads or changes on top of the original map. Similarly, LoRA adds small, lightweight modifications to AI model weights rather than changing all billions of parameters, achieving the same navigation updates with a tiny fraction of the effort and storage. What Is the LoRA Principle? LoRA decomposes weight updates into low-rank matrices dramatically reducing trainable parameters. Mathematical foundation: ΔW = BA where B ∈ R^(d×r), A ∈ R^(r×k) with rank r << min(d,k). Original weights frozen: W' = W + ΔW keeping pre-trained weights unchanged. Rank bottleneck: typical r = 4-64 creating information compression. Parameter reduction: from d×k to r×(d+k), often 10,000x fewer parameters. Linear reparameterization: maintaining model architecture without structural changes. Hypothesis: weight updates have low intrinsic rank during adaptation. How Does LoRA Training Work? Training LoRA involves updating only the low-rank matrices while keeping base model frozen. Initialization: A ~ N(0, σ²), B = 0 ensuring zero initial modification. Forward pass: h = (W + BA)x computing modified output. Gradient flow: backpropagation only through B and A matrices. Learning rate: higher than full fine-tuning, typically 1e-3 to 1e-4. Scaling factor: α/r controlling update magnitude, crucial hyperparameter. Memory efficiency: storing only gradients for BA not full W.