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An Introduction to Reinforcement Learning for Beginners

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Harshini Bhat

Data Science Consultant at almaBetter

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Published on05 Jun, 2023

Have you ever wondered how machines learn to make decisions on their own? One way is through Reinforcement Learning, a subfield of Artificial Intelligence that allows machines to learn by trial and error. By rewarding desirable behavior and penalizing undesirable behavior, these machines can eventually learn to make decisions that lead to optimal outcomes. In this article, we will take a closer look at Reinforcement Learning in Machine Learning, its basic terminologies, algorithms, types, and practical applications. Whether you're a beginner or an experienced professional, join us as we explore the fascinating world of Reinforcement Learning

What is Reinforcement Learning?

Reinforcement learning in Machine Learning is a fascinating approach to teaching machines how to learn through trial and error. It's like how a baby takes its first steps, but instead of a baby, it's a computer agent learning to navigate a complex environment.

The technical aspect of reinforcement learning involves building an agent that can perceive and interpret its environment, take actions based on that interpretation, and receive feedback in the form of rewards or punishments.

Let's say you want to train an agent to play a game of chess. The agent's goal is to win the game, and it learns by playing against itself or other opponents. Each time it makes a move, the agent receives feedback in the form of points or rewards, depending on whether the move was good or bad. Over time, the agent learns to associate certain moves with positive rewards and others with negative rewards, and it adjusts its strategy accordingly.

Reinforcement Learning

Reinforcement Learning

This learning process is made possible by a mathematical model known as the Markov Decision Process (MDP), which provides a framework for representing and solving decision-making problems. MDPs use probability theory to model the uncertainty inherent in decision-making problems, and reinforcement learning algorithms use MDPs to learn the optimal policy for a given task.

Now Let us see, How does it work in more detail.

How Does Reinforcement Learning Work?

We will understand better with an example of a student learning in a classroom. Imagine a student who is trying to learn a subject but has no teacher to guide them. The student must learn through trial and error by experimenting with different approaches to the subject and seeing which ones yield positive results (better grades) and which ones yield negative results (worse grades).

In this scenario, the student is the agent, the subject is the environment, and the grades are the rewards. The student's goal is to maximize their grades, just as an agent in reinforcement learning seeks to maximize its reward. The student may try different study strategies, such as taking notes or working through practice problems, and will adjust their approach based on the feedback they receive (grades). Over time, the student learns what works and what doesn't and can apply this knowledge to future assignments and exams.

Similarly, in reinforcement learning, an agent tries different actions in an environment and receives feedback in the form of rewards or punishments. The agent adjusts its approach based on this feedback, learning over time how to take the actions that will yield the highest reward. With enough trial and error, the agent can become highly skilled at its task and make optimal decisions in complex environments.

Basic Terminologies Used in Reinforcement Learning:

Here are some basic terminologies that are used in reinforcement learning:

  1. Agent: The entity or system that takes actions in an environment to achieve a goal.
  2. Environment: The external system that interacts with the agent and provides feedback in the form of rewards.
  3. State: The current condition of the environment or the agent that includes all the relevant information necessary for decision-making.
  4. Action: The decision made by the agent in a particular state of the environment.
  5. Reward: The feedback or signal provided to the agent by the environment for a particular action in a particular state.
  6. Policy: The decision-making function of the agent that maps states to actions.
  7. Value Function: The expected long-term reward that an agent would receive from a particular state and policy.
  8. Q-value: The expected long-term reward that an agent would receive from a particular state and action.
  9. Exploration-Exploitation Tradeoff: The balance between trying out new actions to gain more information (exploration) and taking actions based on the current information available (exploitation).
  10. Discount Factor: A value that reduces the weightage of future rewards in comparison to immediate rewards, as future rewards are uncertain.

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Basics of Reinforcement Learning

Reinforcement Learning Workflow

The workflow for reinforcement learning can be broken down into several steps:

  1. Define the problem: Define the problem you want to solve and identify the goals or objectives you want to achieve.
  2. Design the environment: Create an environment where the agent will operate. The environment should include all the variables that will affect the agent's decision-making process.
  3. Define the reward function: Define the reward function that will be used to evaluate the agent's actions. The reward function should be designed to encourage the agent to take actions that will lead to achieving the defined goals or objectives.
  4. Define the agent: Design the agent that will operate in the environment. The agent should be able to observe the environment, take actions based on its observations, and receive feedback in the form of rewards.
  5. Train the agent: Train the agent using reinforcement learning techniques. The agent will interact with the environment, receive feedback in the form of rewards, and use that feedback to update its decision-making process.
  6. Test the agent: Test the agent in the environment to evaluate its performance. This will help you determine if the agent is making decisions that lead to achieving the defined goals or objectives.
  7. Deploy the agent: Deploy the trained agent in the real-world environment to solve the problem and achieve the goals or objectives.

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Throughout the entire process, it is important to monitor the agent's performance and make adjustments as necessary to improve its decision-making process.

Characteristics of Reinforcement Learning.

The following are the features of Reinforcement Learning.

  • No supervision, only a real value or reward signal: Unlike in supervised learning, where the training data includes input-output pairs, in reinforcement learning, the agent only receives a scalar reward signal for each action it takes. This signal indicates how good or bad the action was but does not specify what the correct action should be.
  • Decision-making is sequential: Reinforcement learning involves making a sequence of decisions over time, where each decision affects the next state and reward signal.
  • Time: Since decisions in reinforcement learning affect future rewards, the timing of decisions can be critical to achieving optimal performance.
  • Feedback isn't prompt but delayed: In many reinforcement learning tasks, the reward signal is only received after a sequence of actions has been taken. This means that the agent must learn to associate its actions with future rewards that may be delayed in time.
  • The following data it receives is determined by the agent's actions: In reinforcement learning, the agent interacts with an environment and receives new data based on its own actions. This means that the agent must learn to balance exploration (trying out new actions to learn more about the environment) and exploitation (taking actions that are expected to yield high rewards based on previous experience).

Reinforcement Learning Algorithms

Reinforcement learning algorithms can be broadly categorized into two approaches to be implemented:

  1. Model-based Reinforcement Learning: In this type, the agent learns a model of the environment, including the possible states, actions, and rewards. This model is then used to plan the agent's future actions based on the predicted outcomes.
  2. Model-free Reinforcement Learning: In this type, the agent directly learns the optimal policy without explicitly modeling the environment. The agent learns by trial and error through interacting with the environment and receiving feedback in the form of rewards. The two subcategories of model-free RL are:
  • Value-based RL: In this approach, the agent learns to estimate the value of each state or state-action pair and then selects actions based on the maximum expected value.
  • Policy-based RL: In this approach, the agent learns a policy that maps states to actions directly without estimating the value of each state.

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Reinforcement learning algorithms

Types of Reinforcement Learning:

There are two types - Positive Reinforcement Learning and Negative Reinforcement Learning.

Positive reinforcement: It is a type of reinforcement learning where behavior is strengthened by rewarding it with something positive. This then increases the likelihood of the behavior being repeated in the future.

Advantages:

  • Increases the strength and frequency of desired behavior
  • Improves performance of an action
  • Creates sustained change over a longer period of time

Disadvantage:

  • Excessive reinforcement can lead to overload and diminish results

Negative Reinforcement: Negative reinforcement is a type of reinforcement learning where behavior is strengthened by removing or avoiding something negative, such as an unpleasant sensation or situation. This also increases the likelihood of the behavior being repeated in the future.

Advantages of negative reinforcement:

  • It maximizes the desired behavior.
  • It ensures a decent minimum standard of performance.

Disadvantage of negative reinforcement:

  • It only limits itself to meeting the minimum required behavior and may not encourage further improvement.

Applications of Reinforcement Learning

Some of the most widely used applications of reinforcement learning include:

  1. Robotics for industrial automation: Reinforcement learning is used to train robots for various tasks in industrial settings, such as picking and placing objects or assembly line tasks.
  2. Autonomous self-driving cars: Reinforcement learning is used to train autonomous cars to make decisions based on real-time traffic and environmental data.
  3. Game playing: Reinforcement learning algorithms have been used to create intelligent agents that can play games such as Chess, Go, and Atari games.
  4. Text summarization and dialogue agents: Reinforcement learning is used to create text summarization engines and dialogue agents for natural language processing applications.
  5. Recommendation systems: Reinforcement learning is used to optimize recommendation systems that give different users suggestions about products or services based on their past behavior and preferences.

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Applications of Reinforcement Learning

These are a few examples of the practical applications of reinforcement learning, and the field is rapidly expanding with new and innovative use cases.

Conclusion

Reinforcement learning is a type of machine learning that enables an agent to learn how to behave in an environment through trial and error. It uses feedback in the form of rewards or punishments to guide the agent's actions. Reinforcement learning algorithms can be categorized into three main approaches, including deep reinforcement learning. Positive and negative reinforcement are two types of reinforcement learning. Reinforcement Learning has practical applications in various fields, such as robotics, self-driving cars, and artificial intelligence. As technology advances, more innovative applications of Reinforcement Machine Learning in different industries are expected to emerge.

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