Hidden States as Value Gradients: The Pontryagin Structure of Recurrent Policies
A key capability of intelligent agents is to act effectively under incomplete state observations. Recurrent policies address this by compressing observation histories into a hidden state. In this work, we show that the hidden state of a recurrent policy admits a control-theoretic interpretation: it plays the role of the co-state in Pontryagin's minimum principle, and the readout that maps it to actions implements control-Hamiltonian minimization. The hidden state thus tracks the gradient of the value function, encoding the optimality structure of the underlying control problem. We formalize this correspondence through a class of policies we refer to as co-state policies (CPs) and show tha...
| Authors | David Leeftink, Max Hinne, Marcel van Gerven |
|---|---|
| Primary category | cs.LG |
| Published | 6 May 2026 |
| Last updated at source | 28 September 2026 |
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