#
Glossary

This is a community-created glossary. Contributions are welcome!

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Agent

An agent learns to make decisions by trial and error, with rewards and punishments from the surroundings.

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Environment

An environment is a simulated world where an agent can learn by interacting with it.

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Markov Property

It implies that the action taken by our agent is conditional solely on the present state and independent of the past states and actions.

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Observations/State

- State: Complete description of the state of the world.
- Observation: Partial description of the state of the environment/world.

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Actions

- Discrete Actions: Finite number of actions, such as left, right, up, and down.
- Continuous Actions: Infinite possibility of actions; for example, in the case of self-driving cars, the driving scenario has an infinite possibility of actions occurring.

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Rewards and Discounting

- Rewards: Fundamental factor in RL. Tells the agent whether the action taken is good/bad.
- RL algorithms are focused on maximizing the cumulative reward.
- Reward Hypothesis: RL problems can be formulated as a maximisation of (cumulative) return.
- Discounting is performed because rewards obtained at the start are more likely to happen as they are more predictable than long-term rewards.

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Tasks

- Episodic: Has a starting point and an ending point.
- Continuous: Has a starting point but no ending point.

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Exploration v/s Exploitation Trade-Off

- Exploration: It’s all about exploring the environment by trying random actions and receiving feedback/returns/rewards from the environment.
- Exploitation: It’s about exploiting what we know about the environment to gain maximum rewards.
- Exploration-Exploitation Trade-Off: It balances how much we want to explore the environment and how much we want to exploit what we know about the environment.

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Policy

- Policy: It is called the agent’s brain. It tells us what action to take, given the state.
- Optimal Policy: Policy that maximizes the expected return when an agent acts according to it. It is learned through training.

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Policy-based Methods:

- An approach to solving RL problems.
- In this method, the Policy is learned directly.
- Will map each state to the best corresponding action at that state. Or a probability distribution over the set of possible actions at that state.

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Value-based Methods:

- Another approach to solving RL problems.
- Here, instead of training a policy, we train a value function that maps each state to the expected value of being in that state.

Contributions are welcome 🤗

If you want to improve the course, you can open a Pull Request.

This glossary was made possible thanks to:

- @lucifermorningstar1305
- @daspartho
- @misza222

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