Fine-tune Language Models to Approximate Unbiased In-context Learning
Timothy Chu Zhao Song Chiwun Yang
In-context learning (ICL) is an astonishing emergent ability of large
language models (LLMs). By presenting a prompt that includes multiple
input-output pairs as examples and introducing a new query input, models can
generate the corresponding output. However, the performance of models heavily
relies on the quality of the input prompt when implementing in-context
learning. Biased or imbalanced input prompts can significantly degrade the
performance of language models. To address this issue, we introduce a
reweighted algorithm called RICL (Reweighted In-context Learning). This
algorithm fine-tunes language models using an unbiased validation set to
determine the optimal weight for each input-output example to approximate
unbiased in-context learning. Furthermore, we also introduce a low-cost
reweighted algorithm, a linear optimal weight approximation algorithm called
LARICL (Linear Approximation of Reweighted In-context Learning). This algorithm
requires minimal training cost while providing effective results. We prove the
convergence of our algorithm and validate its performance through experiments
conducted on a numerical dataset. The experimental findings reveal a
substantial improvement in comparison to benchmarks including the performance
of casual prompt-based in-context learning and the performance of a classic
fine-tuning method.