Actor-Critic Method

Actor-Critic Method

The Actor-Critic Method is a reinforcement learning (RL) algorithm that combines the strengths of value-based and policy-based methods. It’s a type of model-free algorithm that uses two neural networks: the actor, which decides the action to take, and the critic, which evaluates the action taken by the actor.


The Actor-Critic Method is a powerful tool in the field of reinforcement learning. It’s a hybrid approach that leverages the strengths of both policy-based and value-based methods. The actor network is responsible for determining the optimal action given a state, while the critic network evaluates the quality of the action taken by the actor. This dual approach allows the algorithm to learn more efficiently and effectively.

How it Works

The Actor-Critic Method operates in a continuous loop of action and feedback. The actor network takes the current state of the environment as input and outputs a policy, which is a probability distribution over actions. The action is then chosen according to this policy.

The chosen action is applied to the environment, resulting in a new state and a reward. The critic network takes the new state and the reward as input and outputs a value, which is an estimate of the expected return from the current state.

The actor network is then updated to maximize the expected return, using the value output by the critic network as a baseline to reduce variance. The critic network is updated to minimize the difference between its value estimates and the actual returns.


The Actor-Critic Method has been used in a wide range of applications, from game playing to robotics. It’s particularly effective in environments with large state and action spaces, where traditional RL methods may struggle. For example, it has been used to train agents to play complex video games and to control robotic arms in simulation.

Advantages and Disadvantages

The main advantage of the Actor-Critic Method is its efficiency. By using a critic network to provide a baseline, it reduces the variance of the policy gradient, leading to faster and more stable learning. It also allows for continuous action spaces, which are common in many real-world problems.

However, the Actor-Critic Method also has some disadvantages. It requires two networks to be trained simultaneously, which can be computationally expensive. It’s also more complex than simpler RL methods, which can make it harder to implement and debug.

Key Takeaways

The Actor-Critic Method is a powerful reinforcement learning algorithm that combines the strengths of policy-based and value-based methods. It uses two networks, an actor and a critic, to learn more efficiently and effectively. Despite its complexity and computational cost, it’s a valuable tool for tackling complex RL problems.


  1. Sutton, R. S., & Barto, A. G. (2018). Reinforcement learning: An introduction. MIT press.
  2. Mnih, V., et al. (2016). Asynchronous methods for deep reinforcement learning. In International conference on machine learning (pp. 1928-1937). PMLR.
  3. Lillicrap, T. P., et al. (2015). Continuous control with deep reinforcement learning. arXiv preprint arXiv:1509.02971.