def sarsa(env,
estimator,
num_episodes,
statistics,
discount_factor=1.0,
epsilon=0.1,
epsilon_decay=1.0):
"""
sarsa algorithm for on-policy TD control using Function Approximation.
Args:
env: OpenAI environment.
estimator: Action-Value function estimator
num_episodes: Number of episodes to run for.
An EpisodeStats object with two numpy arrays for episode_lengths and episode_rewards.
discount_factor: Lambda time discount factor.
epsilon: Chance the sample a random action. Float betwen 0 and 1.
epsilon_decay: Each episode, epsilon is decayed by this factor
Returns:
"""
for i_episode in range(num_episodes):
# The policy we're following
e_greedy_policy = utility.make_epsilon_greedy_policy_with_fa(
estimator, epsilon * epsilon_decay**i_episode, env.action_space.n)
# Print out which episode we're on, useful for debugging.
# Also print reward for last episode
last_reward = statistics.episode_rewards[i_episode - 1]
sys.stdout.flush()
# Reset the environment and pick the first action
obvservation = env.reset()
action = utility.make_decision(e_greedy_policy, obvservation)
for t in itertools.count():
next_observation, reward, done, _ = env.step(action)
# Update statistics
statistics.episode_rewards[i_episode] += reward
statistics.episode_lengths[i_episode] = t
next_action = utility.make_decision(e_greedy_policy,
next_observation)
q_values_next = estimator.predict(next_observation, next_action)
td_target = reward + discount_factor * q_values_next
# Update the function approximator using our target
estimator.update(obvservation, action, td_target)
print("\rStep {} @ Episode {}/{} ({})".format(
t, i_episode + 1, num_episodes, last_reward),
end="")
if done:
break
action = next_action
obvservation = next_observation
def q_learning(env, num_episodes, statistics, discount_factor=1.0, alpha=0.5, epsilon=0.1):
"""
Q-Learning algorithm: Off-policy TD control. Finds the optimal greedy policy
while following an epsilon-greedy policy
Args:
env: OpenAI environment.
num_episodes: Number of episodes to run for.
discount_factor: Lambda time discount factor.
alpha: TD learning rate.
epsilon: Chance the sample a random action. Float betwen 0 and 1.
Returns:
Q is the optimal action-value function, a dictionary mapping state -> action values.
stats is an EpisodeStats object with two numpy arrays for episode_lengths and episode_rewards.
"""
# The final action-value function.
# A nested dictionary that maps state -> (action -> action-value).
Q = defaultdict(lambda: np.zeros(env.action_space.n))
# The policy we're following
e_greedy_policy = utility.make_epsilon_greedy_policy(Q, epsilon, env.action_space.n)
for i_episode in range(num_episodes):
# Print out which episode we're on, useful for debugging.
if (i_episode + 1) % 100 == 0:
print("\rEpisode {}/{}.".format(i_episode + 1, num_episodes), end="")
sys.stdout.flush()
# Reset the environment and pick the first action
state = env.reset()
# One step in the environment
# total_reward = 0.0
for t in itertools.count():
# Take a step
action = utility.make_decision(e_greedy_policy, state)
next_state, reward, done, _ = env.step(action)
# Update statistics
statistics.episode_rewards[i_episode] += reward
statistics.episode_lengths[i_episode] = t
# TD Update
best_next_action = np.argmax(Q[next_state])
td_target = reward + discount_factor * \
Q[next_state][best_next_action]
td_delta = td_target - Q[state][action]
Q[state][action] += alpha * td_delta
if done:
break
state = next_state
return Q
def run_episode(env, greedy_policy):
observation = env.reset()
for t in itertools.count():
env.render()
action = utility.make_decision(greedy_policy, observation)
ob, reward, done, info = env.step(action)
if done:
break
observation = ob
def mc_control_epsilon_greedy(env, num_episodes, statistics, discount_factor=1.0, epsilon=0.1):
"""
Monte Carlo Control using Epsilon-Greedy policies.
Finds an optimal epsilon-greedy policy.
Args:
env: OpenAI gym environment.
num_episodes: Nubmer of episodes to sample.
statistics: namedTuple of statistics informaiton
discount_factor: Lambda discount factor.
epsilon: Chance the sample a random action. Float betwen 0 and 1.
Returns:
A tuple (Q, policy).
Q is a dictionary mapping state -> action values.
policy is a function taht takes an observation as an argument and returns
action probabilities
"""
# Keeps track of sum and count of returns for each state
# to calculate an average. We could use an array to save all
# returns (like in the book) but that's memory inefficient.
returns_sum = defaultdict(float)
returns_count = defaultdict(float)
# The final action-value function.
# A nested dictionary that maps state -> (action -> action-value).
Q = defaultdict(lambda: np.zeros(env.action_space.n))
# The policy we're following
policy = utility.make_epsilon_greedy_policy(Q, epsilon, env.action_space.n)
for i_episode in range(num_episodes):
# Print out which episode we're on, useful for debugging.
if i_episode % 100 == 0:
print("\rEpisode {}/{}.".format(i_episode, num_episodes), end="")
sys.stdout.flush()
# Generate an episode.
# An episode is an array of (state, action, reward) tuples
episode = []
state = env.reset()
for t in itertools.count():
action = utility.make_decision(policy, state)
next_state, reward, done, _ = env.step(action)
# Update statistics
statistics.episode_rewards[i_episode] += reward
statistics.episode_lengths[i_episode] = t
episode.append((state, action, reward))
if done:
break
state = next_state
# Find all (state, action) pairs we've visited in this episode
# We convert each state to a tuple so that we can use it as a dict key
# the tuple is (state,action)
state_action_in_episode = set([(x[0], x[1]) for x in episode])
for state, action in state_action_in_episode:
state_action = (state, action)
# Find the first occurance of the (state, action) pair in the episode
first_occurence_idx = next(i for i, x in enumerate(episode)
if x[0] == state and x[1] == action)
# Sum up all rewards since the first occurance
G = sum([x[2] * (discount_factor**i)
for i, x in enumerate(episode[first_occurence_idx:])])
# Calculate average return for this state over all sampled episodes
returns_sum[state_action] += G
returns_count[state_action] += 1.0
Q[state][action] = returns_sum[state_action] / \
returns_count[state_action]
# The policy is improved implicitly by changing the Q dictionar
return Q
def expected_sarsa(env, num_episodes, statistics, discount_factor=1.0, alpha=0.5, epsilon=0.1):
"""
Q-expected_sarsa algorithm: on-policy TD control. Finds the optimal epsilon-greedy policy
Args:
env: OpenAI environment.
num_episodes: Number of episodes to run for.
statistics: An EpisodeStats object with two numpy arrays for episode_lengths and episode_rewards.
discount_factor: Lambda time discount factor.
alpha: TD learning rate.
epsilon: Chance the sample a random action. Float betwen 0 and 1.
Returns:
Q is the optimal action-value function, a dictionary mapping state -> action values.
stats is an EpisodeStats object with two numpy arrays for episode_lengths and episode_rewards.
"""
# The final action-value function.
# A nested dictionary that maps state -> (action -> action-value).
q = defaultdict(lambda: np.zeros(env.action_space.n))
# The policy we're following
e_greedy_policy = utility.make_epsilon_greedy_policy(q, epsilon, env.action_space.n)
for i_episode in range(num_episodes):
# Print out which episode we're on, useful for debugging.
if (i_episode + 1) % 100 == 0:
print("\rEpisode {}/{}.".format(i_episode + 1, num_episodes), end="")
sys.stdout.flush()
# Reset the environment and pick the first action
observation = env.reset()
# One step in the environment
for t in itertools.count():
# Take a step
action = utility.make_decision(e_greedy_policy, observation)
next_observation, reward, done, _ = env.step(action)
# Update statistics
statistics.episode_rewards[i_episode] += reward
statistics.episode_lengths[i_episode] = t
expected_next_q = 0
next_actions = e_greedy_policy(next_observation)
for action, action_prob in enumerate(next_actions):
expected_next_q += action_prob * q[next_observation][action]
td_target = reward + discount_factor * expected_next_q
td_delta = td_target - q[observation][action]
q[observation][action] += alpha * td_delta
if done:
break
observation = next_observation
return q