dqn_agent.DQNAgent

Class DQNAgent

An implementation of the DQN agent.

Methods

init

__init__(
    *args,
    **kwargs
)

Initializes the agent and constructs the components of its graph.

Args:

• sess: tf.Session, for executing ops.
• num_actions: int, number of actions the agent can take at any
  state.
• gamma: float, discount factor with the usual RL meaning.
• update_horizon: int, horizon at which updates are performed, the
  ‘n’ in n-step update.
• min_replay_history: int, number of transitions that should be
  experienced before the agent begins training its value function.
• update_period: int, period between DQN updates.
• target_update_period: int, update period for the target network.
• epsilon_fn: function expecting 4 parameters: (decay_period, step,
  warmup_steps, epsilon). This function should return the epsilon value used
  for exploration during training.
• epsilon_train: float, the value to which the agent’s epsilon is
  eventually decayed during training.
• epsilon_eval: float, epsilon used when evaluating the agent.
• epsilon_decay_period: int, length of the epsilon decay schedule.
• tf_device: str, Tensorflow device on which the agent’s graph is
  executed.
• use_staging: bool, when True use a staging area to prefetch the
  next training batch, speeding training up by about 30%.
• max_tf_checkpoints_to_keep: int, the number of TensorFlow
  checkpoints to keep.
• optimizer: tf.train.Optimizer, for training the value function.

begin_episode

begin_episode(observation)

Returns the agent’s first action for this episode.

Args:

• observation: numpy array, the environment’s initial observation.

Returns:

int, the selected action.

bundle_and_checkpoint

bundle_and_checkpoint(
    checkpoint_dir,
    iteration_number
)

Returns a self-contained bundle of the agent’s state.

This is used for checkpointing. It will return a dictionary containing all
non-TensorFlow objects (to be saved into a file by the caller), and it saves all
TensorFlow objects into a checkpoint file.

Args:

• checkpoint_dir: str, directory where TensorFlow objects will be
  saved.
• iteration_number: int, iteration number to use for naming the
  checkpoint file.

Returns:

A dict containing additional Python objects to be checkpointed by the
experiment. If the checkpoint directory does not exist, returns None.

end_episode

end_episode(reward)

Signals the end of the episode to the agent.

We store the observation of the current time step, which is the last observation
of the episode.

Args:

• reward: float, the last reward from the environment.

step

step(
    reward,
    observation
)

Records the most recent transition and returns the agent’s next action.

We store the observation of the last time step since we want to store it with
the reward.

Args:

• reward: float, the reward received from the agent’s most recent
  action.
• observation: numpy array, the most recent observation.

Returns:

int, the selected action.

unbundle

unbundle(
    checkpoint_dir,
    iteration_number,
    bundle_dictionary
)

Restores the agent from a checkpoint.

Restores the agent’s Python objects to those specified in bundle_dictionary, and
restores the TensorFlow objects to those specified in the checkpoint_dir. If the
checkpoint_dir does not exist, will not reset the agent’s state.

Args:

• checkpoint_dir: str, path to the checkpoint saved by tf.Save.
• iteration_number: int, checkpoint version, used when restoring
  replay buffer.
• bundle_dictionary: dict, containing additional Python objects owned
  by the agent.

Returns:

bool, True if unbundling was successful.