Supervised Fine-Tuning (SFT) is a technique used to adapt a pre-trained Large Language Model (LLM) to a specific downstream task using labeled data. Let’s break it down:
Pre-Trained LLM:
- Initially, we have a pre-trained language model (like GPT-3 or Phi-3) that has learned from a large corpus of text data.
- This pre-trained model has already acquired knowledge about language, grammar, and context.
Adapting to a Specific Task:
- To make the model useful for a specific task (e.g., answering questions, generating code, or translating text), we fine-tune it.
- Fine-tuning involves training the model further on a smaller dataset specific to the task.
Labeled Dataset:
- We provide the model with a labeled dataset.
- Each example in this dataset consists of an input (e.g., a prompt or question) and its corresponding correct output (label).
Training Process:
- During fine-tuning, the model learns to predict the correct label for each input.
- It adjusts its parameters based on the labeled examples, effectively adapting its knowledge to the specific task.
SFTTrainer:
- The SFTTrainer class from libraries like Hugging Face’s Transformer Reinforcement Learning (TRL) facilitates the SFT process.
- It accepts a column in the training dataset CSV containing system instructions, questions, and answers (forming the prompt structure).
- Different models may require different prompt structures, but a standard approach is to use the dataset structure described in OpenAI’s InstructGPT paper.
In summary, SFT allows us to fine-tune a pre-trained model to perform well on a specific task by leveraging labeled data.
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