Diverse Preference Optimization

Introduces Diverse Preference Optimization (DivPO), a novel training method that aims to address the lack of diversity in language model outputs while maintaining response quality. The key challenge is that current preference optimization techniques like RLHF tend to sharpen the output probability distribution, causing models to generate very similar responses. This is particularly problematic for creative tasks where varied outputs are desired. DivPO works by modifying how training pairs are selected during preference optimization. Rather than simply choosing the highest and lowest rewarded responses, DivPO selects the most diverse response that meets a quality threshold and contrasts it with the least diverse response below a threshold. The method introduces a diversity criterion that can be measured in different ways, including model probability, word frequency, or using an LLM as a judge. Experiments on persona generation and creative writing tasks show that DivPO achieves up to 45.6% more diverse outputs in structured tasks and an 81% increase in story diversity, while maintaining similar quality levels compared to baseline methods.