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3.6 KiB
3.6 KiB
Sure! Below is an example script that demonstrates the SARSA (State-Action-Reward-State-Action) algorithm using a simple grid world environment:
import numpy as np
# Define the grid world environment
grid = [
[0, 0, 0, 0],
[0, -1, 0, -1],
[0, 0, 0, -1],
[0, -1, 0, 1]
]
# Initialize Q-table
Q = np.zeros((4, 4, 4)) # Q(s, a) - 4x4 grid, 4 actions (up, down, left, right)
# Define epsilon-greedy exploration
epsilon = 0.1
# Define learning parameters
alpha = 0.1 # Learning rate
gamma = 0.9 # Discount factor
# Define action mapping
actions = ['up', 'down', 'left', 'right']
# Get next action using epsilon-greedy exploration
def get_action(state):
if np.random.rand() < epsilon:
action = np.random.choice(actions)
else:
action = actions[np.argmax(Q[state[0], state[1]])]
return action
# Update Q-values using SARSA algorithm
def update_q_values(state, action, reward, next_state, next_action):
Q[state[0], state[1], actions.index(action)] += alpha * (
reward + gamma * Q[next_state[0], next_state[1], actions.index(next_action)] -
Q[state[0], state[1], actions.index(action)])
# Train the agent
def train_agent():
num_episodes = 1000
for episode in range(num_episodes):
state = [3, 0] # Start state
action = get_action(state)
while True:
# Perform selected action
if action == 'up':
next_state = [state[0] - 1, state[1]]
elif action == 'down':
next_state = [state[0] + 1, state[1]]
elif action == 'left':
next_state = [state[0], state[1] - 1]
else:
next_state = [state[0], state[1] + 1]
# Check if next state is valid
if next_state[0] < 0 or next_state[0] >= 4 or next_state[1] < 0 or next_state[1] >= 4:
next_state = state
# Get next action using epsilon-greedy exploration
next_action = get_action(next_state)
# Update Q-values
update_q_values(state, action, grid[next_state[0]][next_state[1]], next_state, next_action)
# Update current state and action
state = next_state
action = next_action
# Break if goal state reached
if grid[state[0]][state[1]] == 1:
break
# Test the trained agent
def test_agent():
state = [3, 0] # Start state
while True:
# Choose the best action based on Q-values
action = actions[np.argmax(Q[state[0], state[1]])]
# Perform selected action
if action == 'up':
next_state = [state[0] - 1, state[1]]
elif action == 'down':
next_state = [state[0] + 1, state[1]]
elif action == 'left':
next_state = [state[0], state[1] - 1]
else:
next_state = [state[0], state[1] + 1]
# Print the current state and action taken
print(f"Current state: {state}, Action: {action}")
# Update current state
state = next_state
# Break if goal state reached
if grid[state[0]][state[1]] == 1:
print("Reached the goal!")
break
# Train and test the agent
train_agent()
test_agent()
This script demonstrates SARSA algorithm in a simple grid world environment, where the agent has to navigate from the starting state [3, 0]
to the goal state [3, 3]
while avoiding obstacles represented by -1
. The agent uses the SARSA algorithm to learn optimal Q-values and then applies them to reach the goal state.