middle-focused positional encoding
An Efficient Recipe for Long Context Extension via Middle-Focused Positional Encoding
Recently, many methods have been developed to extend the context length of pre-trained large language models (LLMs), but they often require fine-tuning at the target length ( \gg4K) and struggle to effectively utilize information from the middle part of the context. Apart from being simple, \texttt{CREAM} is training-efficient: it only requires fine-tuning at the pre-trained context window (e.g., Llama 2-4K) and can extend LLMs to a much longer target context length (e.g., 256K). To ensure that the model focuses more on the information in the middle, we introduce a truncated Gaussian to encourage sampling from the middle part of the context during fine-tuning, thus alleviating the ''Lost-in-the-Middle'' problem faced by long-context LLMs. Experimental results show that \texttt{CREAM} successfully extends LLMs to the target length for both Base and Chat versions of \texttt{Llama2-7B} with Never Miss A Beat''.