src/llms/finetuning.qmd

# Fine-Tuning and Lora

Fine-tuning and LoRA (Low-Rank Adaptation) are two approaches commonly used to adapt Large Language Models (LLMs) to specific tasks or datasets. These methods are crucial for leveraging the power of pre-trained models and making them more effective for particular applications without needing to train a model from scratch.

## Fine-Tuning in LLMs

**Fine-tuning** is a process where a pre-trained model is further trained (or "fine-tuned") on a new dataset with a possibly different but related task. This approach leverages the learned features and knowledge the model has acquired during its initial training on a vast corpus of data, typically involving general tasks like language modeling.

### How Fine-Tuning Works
1. **Start with a Pre-trained Model**: Begin with a model that has been pre-trained on a large dataset to learn a wide range of language patterns and tasks.
2. **Continue Training**: The model is further trained on a smaller, specific dataset. This dataset is task-specific, meaning it directly relates to the tasks the model needs to perform in its deployment environment.
3. **Adjust Weights**: During fine-tuning, most or all of the neural network layers are adjusted. The learning rate is typically much lower during this phase to make smaller adjustments to the weights, which helps in refining the model’s capabilities without losing the generalized knowledge it has previously acquired.
4. **Task-Specific Adjustments**: The output layer often undergoes significant changes, especially if the new task differs in nature (e.g., from classification to regression).

Fine-tuning allows the model to specialize towards specific nuances of a new task or dataset, enhancing its performance on particular domains or problems.

## LoRA in LLMs

**LoRA (Low-Rank Adaptation)** is a more recent and less resource-intensive approach compared to traditional fine-tuning. It introduces task-specific trainable parameters while freezing most of the pre-trained parameters. This method is particularly useful for adapting large models efficiently with fewer trainable parameters.

### How LoRA Works
1. **Modify Architecture**: LoRA introduces low-rank matrices to the architecture of a pre-trained model. Instead of updating the original weight matrices of the model, LoRA adds trainable rank-decomposition matrices that capture the task-specific deviations from the pre-trained setup.
2. **Train Few Parameters**: In LoRA, you train these additional low-rank matrices while keeping the original high-dimensional weight matrices frozen. This reduces the number of trainable parameters significantly.
3. **Parameter Efficiency**: The key advantage of LoRA is that it allows for the efficient tuning of large models without the need to re-train or fine-tune millions of parameters. This makes it computationally cheaper and faster while still leveraging the power of large-scale pre-training.
4. **Integration**: The low-rank matrices are integrated into the model during the forward pass, modifying the model's behavior dynamically based on the learned task-specific adjustments.

## Comparison and Use Cases

- **Fine-Tuning**: More comprehensive and potentially more powerful as it adapts all model weights to the new task, but it is resource-intensive. Ideal for situations where you have sufficient computational resources and the task-specific dataset is large enough to warrant extensive re-training.
- **LoRA**: Best suited for scenarios where computational resources are limited, or you need to quickly adapt a large model to multiple specific tasks. LoRA is also beneficial when you need to maintain the original model’s integrity and avoid catastrophic forgetting that might occur during extensive fine-tuning.

Both fine-tuning and LoRA are vital tools in the adaptation of LLMs to specific tasks, offering a balance between leveraging massive pre-trained models and customizing them to meet particular needs effectively.