Rethinking Critic Learning in PPO: Understanding and Mitigating Value Flattening
Value Flattening is identified as an important yet overlooked failure mode of critic learning in standard PPO and a simple sparse supervision strategy can mitigate it; SParse Proximal Policy Optimization is introduced, which applies the value loss to only a few well-separated states in each response to mitigate both ef...
Yi-Zhuo Li, Jian-Hao Yan, Yun Luo et al.
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