Reinforcement Learning

title: Reinforcement Learning

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Reinforcement Learning

Reinforcement Learning refers to a field of Machine Learning that applies to agents that you reinforce by giving them reward and punishment. It gives a nice gradual learning and can simplify the learning of agent in tasks where you cannot determine a proper error value.

Reinforcement learning lies in between supervised and unsupervised learning. While the former has a label and the latter does not, reinforcement learning has sparse time delay labels (rewards). It revolves around creating a mathematical framework that encapsulates the idea of an AI interacting with an environment and time acting as a dimension and learning through trial and error.

A bot is given a task to play Space Invaders, it tries to learn to play it by interacting with game and in return getting a reward for the points that it scored at end of the game. Greater the reward, greater are its chances of doing the similar gameplay. In that way, it learns how to play the game and perform in the best possible way.

In industries robot uses deep reinforcement learning to pick a device from one box and putting it in a container. Whether it succeeds or fails, it memorizes the object and gains knowledge and train’s itself to do this job with great speed and precision. Learning on its own is a kind of reinforcement learning provided the learning is in positive dimension.

The best example, and one which you will hear a lot in this field, is AlphaGo developed by Google. This uses reinforcement learning to learn the patterns, rules and semantics of the board game, Go. This bot defeated the World No. 1 Go player, Lee Sedol, in what was the first time a computer program defeated a professional player. AlphaGo won by 4-1 in a five game series. This was a huge victory for AI and kickstarted the field of Reinforcement learning.

Explore / Exploit:

An important theme in RL is the explore vs. exploit tradeoff. Exploring refers to looking for optimal actions outside of the current chosen action, whereas exploiting refers to maximizing our payoff using our known actions. This is commonly manifested in the “multi-armed bandit” problem. The problem presents a user with X slot machines with unknown payoff distributions and asks: how do you maximize your cumulative payoff over time, given a finite amount of time to pull the slot machines? “Greedy” approaches refer to strategies where the first attractive arm that is found is pursued until the end, but such approaches are theoretically inefficient. A clever balance of potentially costly exploring and efficient exploiting is the optimal solution.

List of Common Algorithms

  1. Temporal Difference (TD)
    • Q-Learning
    • SARSA
  2. Policy Gradient and Actor-Critic Methods
    • A3C
    • DDPG

Use cases:

Some applications of the reinforcement learning algorithms are computer played board games (Chess, Go), robotic hands, and self-driving cars.

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