Train your first Deep Q learning-based RL agent: step by step guide | by smit kumbhani |: May, 2023

smit kumbhani
Become human.  Journal of Artificial Intelligence

Reinforcement Learning (RL) is a fascinating area of ​​Artificial Intelligence (AI) that enables machines to learn and make decisions through interactions with their environment. The training of an RL agent involves a trial and error process where the agent learns from its actions and the subsequent rewards or penalties it receives. In this blog, we’ll explore the steps involved in training your first RL agent, as well as code snippets to illustrate the process.

The first step in training an RL agent is to define the environment in which it will operate. The environment can be a simulation or a real-world scenario. It provides observations and rewards to the agent, allowing it to learn and make decisions. OpenAI Gym is a popular Python library that provides a wide variety of pre-built environments. Consider the classic CartPole environment for this example.

import gym

env = gym.make('CartPole-v1')

In RL, an agent interacts with the environment by taking actions based on its observations. It receives feedback in the form of rewards or punishments that are used to guide the learning process. The agent’s objective is to maximize cumulative rewards over time. To do this, the agent learns policies from observations to action mappings that help it make the best decisions.

Various RL algorithms are available, each with its own strengths and weaknesses. One popular algorithm is Q-Learning, which is suitable for discrete operation spaces. Another commonly used algorithm is Deep Q-Networks (DQN), which uses deep neural networks to handle complex environments. For this example, let’s use the DQN algorithm.

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To construct an RL agent with the DQN algorithm, we need to define a neural network as a function approximation. The network takes observations as input and outputs Q values ​​for each possible action. We also need to implement recurrent memory to store and sample experiences for training.

import torch
import torch.nn as nn
import torch.optim as optim

class DQN(nn.Module):
def __init__(self, input_dim, output_dim):
super(DQN, self).__init__()
self.fc1 = nn.Linear(input_dim, 64)
self.fc2 = nn.Linear(64, 64)
self.fc3 = nn.Linear(64, output_dim)

def forward(self, x):
x = torch.relu(self.fc1(x))
x = torch.relu(self.fc2(x))
x = self.fc3(x)
return x

# Create an instance of the DQN agent
input_dim = env.observation_space.shape[0]
output_dim = env.action_space.n
agent = DQN(input_dim, output_dim)

Step 5: Train the RL agent

Now we can train the RL agent using the DQN algorithm. An agent interacts with the environment, observes the current state, chooses an action based on its policy, receives a reward, and updates its Q values ​​accordingly. This process is repeated for a certain number of episodes or until the agent reaches a satisfactory level of performance.

optimizer = optim.Adam(agent.parameters(), lr=0.001)

def train_agent(agent, env, episodes):
for episode in range(episodes):
state = env.reset()
done = False
episode_reward = 0

while not done:
action = agent.select_action(state)
next_state, reward, done, _ = env.step(action)
agent.store_experience(state, action, reward, next_state, done)

In this blog, we explored the process of training your first RL agent. We started by defining the environment using OpenAI Gym, which provides a number of pre-built environments for RL tasks. We then discussed the agent-environment interaction and the agent’s goal of maximizing cumulative rewards.

Next, we selected the DQN algorithm as our RL algorithm of choice, which combines deep neural networks with Q-learning to handle complex environments. We built an RL agent using a neural network as a function approximator and implemented dual memory to store and sample experiences for training.

Finally, we trained the RL agent to interact with the environment, observing states, choosing actions based on its policies, receiving rewards, and updating its Q values. This process was repeated for a certain number of episodes, allowing the agent to learn and improve its decision-making abilities.

Reinforcement learning opens up a world of possibilities for training intelligent agents that can learn autonomously and make decisions in dynamic environments. By following the steps described in this blog, you can begin your journey by training RL agents and exploring different algorithms, environments, and applications.

Remember that learning RL requires experimentation, refinement, and patience. Delving deeper into RL, you can explore advanced techniques such as deep RL, policy gradients, and multiobjective systems. So keep learning, iterating, and pushing the boundaries of what your RL agents can achieve.

Happy training!

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