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The rapid development of large language model (LLM) alignment algorithms has resulted in a complex and fragmented landscape, with limited clarity on the effectiveness of different methods and their inter-connections. This paper introduces…

Proximal Policy Optimization (PPO) methods learn a policy by iteratively performing multiple mini-batch optimization epochs of a surrogate objective with one set of sampled data. Ratio clipping PPO is a popular variant that clips the…

Machine Learning · Computer Science 2022-02-02 Mingfei Sun , Vitaly Kurin , Guoqing Liu , Sam Devlin , Tao Qin , Katja Hofmann , Shimon Whiteson

Preference learning has garnered extensive attention as an effective technique for aligning diffusion models with human preferences in visual generation. However, existing alignment approaches such as Diffusion-DPO suffer from two…

Machine Learning · Computer Science 2026-05-19 Xiaomeng Yang , Mengping Yang , Junyan Wang , Zhijian Zhou , Zhiyu Tan , Hao Li

Policy optimization methods are popular reinforcement learning algorithms, because their incremental and on-policy nature makes them more stable than the value-based counterparts. However, the same properties also make them slow to converge…

Machine Learning · Computer Science 2021-07-01 Andrea Zanette , Ching-An Cheng , Alekh Agarwal

Although Large Language Models (LLMs) have made remarkable progress, current preference optimization methods still struggle to align directional consistency while preserving reasoning diversity. To address this limitation, we propose…

Computation and Language · Computer Science 2026-05-12 Mengyi Deng , Zhiwei Li , Xin Li , Tingyu Zhu , Yulan Yuan , Zhijiang Guo , Wei Wang

Predicting rare extreme events such as wildfires from meteorological data requires models that remain reliable under evolving environmental conditions. This problem is inherently long-tailed: wildfire events are rare but high-impact, while…

Machine Learning · Computer Science 2026-05-13 Enyi Jiang , Wu Sun

Recent advancements have established Reinforcement Learning (RL) as a pivotal paradigm for aligning generative models with human intent. However, group-based optimization frameworks (e.g., GRPO) face a critical limitation: the rapid decay…

Computer Vision and Pattern Recognition · Computer Science 2026-05-18 Sujie Hu , Chubin Chen , Jiashu Zhu , Jiahong Wu , Xiangxiang Chu , Xiu Li

We study model-based offline Reinforcement Learning with general function approximation without a full coverage assumption on the offline data distribution. We present an algorithm named Constrained Pessimistic Policy Optimization…

Machine Learning · Computer Science 2023-01-11 Masatoshi Uehara , Wen Sun

Direct Preference Optimization (DPO) is an efficient alignment technique that steers LLMs towards preferable outputs by training on preference data, bypassing the need for explicit reward models. Its simplicity enables easy adaptation to…

Recommender systems aim to predict personalized rankings based on user preference data. With the rise of Language Models (LMs), LM-based recommenders have been widely explored due to their extensive world knowledge and powerful reasoning…

Information Retrieval · Computer Science 2024-11-08 Yuxin Chen , Junfei Tan , An Zhang , Zhengyi Yang , Leheng Sheng , Enzhi Zhang , Xiang Wang , Tat-Seng Chua

Aligning large language models (LLMs) with human preferences in federated learning (FL) is challenging due to decentralized, privacy-sensitive, and highly non-IID preference data. Direct Preference Optimization (DPO) offers an efficient…

Machine Learning · Computer Science 2026-03-23 Kewen Zhu , Liping Yi , Zhiming Zhao , Zhuang Qi , Han Yu , Qinghua Hu

Current emotional text-to-speech (TTS) models predominantly conduct supervised training to learn the conversion from text and desired emotion to its emotional speech, focusing on a single emotion per text-speech pair. These models only…

Audio and Speech Processing · Electrical Eng. & Systems 2024-09-17 Xiaoxue Gao , Chen Zhang , Yiming Chen , Huayun Zhang , Nancy F. Chen

The rapid advancement of autonomous web navigation has significantly benefited from grounding pretrained Large Language Models (LLMs) as agents. However, current research has yet to fully leverage the redundancy of HTML elements for…

Computation and Language · Computer Science 2024-12-17 Jiarun Liu , Jia Hao , Chunhong Zhang , Zheng Hu

Recently, there has been significant interest in replacing the reward model in Reinforcement Learning with Human Feedback (RLHF) methods for Large Language Models (LLMs), such as Direct Preference Optimization (DPO) and its variants. These…

Computation and Language · Computer Science 2024-09-27 Jian Li , Haojing Huang , Yujia Zhang , Pengfei Xu , Xi Chen , Rui Song , Lida Shi , Jingwen Wang , Hao Xu

Multi-label classification (MLC) often suffers from performance disparities across labels. We propose \textbf{FairPO}, a framework combining preference-based loss and group-robust optimization to improve fairness by targeting…

Machine Learning · Computer Science 2025-12-01 Soumen Kumar Mondal , Prateek Chanda , Akshit Varmora , Ganesh Ramakrishnan

Direct Preference Optimization (DPO) is a method for enhancing model performance by directly optimizing for the preferences or rankings of outcomes, instead of traditional loss functions. This approach has proven effective in aligning Large…

Machine Learning · Computer Science 2024-09-18 Ruoyu Wang , Jiachen Sun , Shaowei Hua , Quan Fang

The ultimate goal of multi-objective optimisation is to help a decision maker (DM) identify solution(s) of interest (SOI) achieving satisfactory trade-offs among multiple conflicting criteria. This can be realised by leveraging DM's…

Neural and Evolutionary Computing · Computer Science 2019-10-01 Ke Li , Minhui Liao , Kalyanmoy Deb , Geyong Min , Xin Yao

Proximal Policy Optimization (PPO) is a highly popular policy-based deep reinforcement learning (DRL) approach. However, we observe that the homogeneous exploration process in PPO could cause an unexpected stability issue in the training…

Machine Learning · Computer Science 2022-12-14 Qisheng Zhang , Zhen Guo , Audun Jøsang , Lance M. Kaplan , Feng Chen , Dong H. Jeong , Jin-Hee Cho

Proximal Policy Optimization (PPO) is a popular deep policy gradient algorithm. In standard implementations, PPO regularizes policy updates with clipped probability ratios, and parameterizes policies with either continuous Gaussian…

Machine Learning · Computer Science 2020-09-24 Chloe Ching-Yun Hsu , Celestine Mendler-Dünner , Moritz Hardt

Direct Preference Optimization (DPO) has been proposed as an effective and efficient alternative to reinforcement learning from human feedback (RLHF). In this paper, we propose a novel and enhanced version of DPO based on curriculum…

Computer Vision and Pattern Recognition · Computer Science 2025-05-12 Florinel-Alin Croitoru , Vlad Hondru , Radu Tudor Ionescu , Nicu Sebe , Mubarak Shah