REINFORCE

REINFORCE is a Monte Carlo variant of a policy gradient algorithm in reinforcement learning. The agent collects samples of an episode using its current policy, and uses it to update the policy parameter $\theta$. Since one full trajectory must be completed to construct a sample space, it is updated as an off-policy algorithm.

$\nabla\_{\theta}J\left(\theta\right) = \mathbb{E}\_{\pi}\left[G\_{t}\nabla\_{\theta}\ln\pi\_{\theta}\left(A\_{t}\mid{S\_{t}}\right)\right]$

Image Credit: Tingwu Wang