def _build_policy_loss(self, i):
"""Build policy loss and other output tensors.
Args:
i (namedtuple): Collection of variables to compute policy loss.
Returns:
tf.Tensor: Policy loss.
tf.Tensor: Mean policy KL divergence.
"""
# pylint: disable=too-many-statements
self._policy_network, self._encoder_network = (self.policy.build(
i.augmented_obs_var, i.task_var, name='loss_policy'))
self._old_policy_network, self._old_encoder_network = (
self._old_policy.build(i.augmented_obs_var,
i.task_var,
name='loss_old_policy'))
self._infer_network = self._inference.build(i.augmented_traj_var,
name='loss_infer')
self._old_infer_network = self._old_inference.build(
i.augmented_traj_var, name='loss_old_infer')
pol_dist = self._policy_network.dist
old_pol_dist = self._old_policy_network.dist
# Entropy terms
encoder_entropy, inference_ce, policy_entropy = (
self._build_entropy_terms(i))
# Augment the path rewards with entropy terms
with tf.name_scope('augmented_rewards'):
rewards = (i.reward_var -
(self.inference_ce_coeff * inference_ce) +
(self._policy_ent_coeff * policy_entropy))
with tf.name_scope('policy_loss'):
with tf.name_scope('advantages'):
adv = compute_advantages(self._discount,
self._gae_lambda,
self.max_episode_length,
i.baseline_var,
rewards,
name='advantages')
adv = tf.reshape(adv, [-1, self.max_episode_length])
# Optionally normalize advantages
eps = tf.constant(1e-8, dtype=tf.float32)
if self._center_adv:
adv = center_advs(adv, axes=[0], eps=eps)
if self._positive_adv:
adv = positive_advs(adv, eps)
# Calculate loss function and KL divergence
with tf.name_scope('kl'):
kl = old_pol_dist.kl_divergence(pol_dist)
pol_mean_kl = tf.reduce_mean(kl)
ll = pol_dist.log_prob(i.action_var, name='log_likelihood')
# Calculate surrogate loss
with tf.name_scope('surr_loss'):
old_ll = old_pol_dist.log_prob(i.action_var)
old_ll = tf.stop_gradient(old_ll)
# Clip early to avoid overflow
lr = tf.exp(
tf.minimum(ll - old_ll, np.log(1 + self._lr_clip_range)))
surrogate = lr * adv
surrogate = tf.debugging.check_numerics(surrogate,
message='surrogate')
# Finalize objective function
with tf.name_scope('loss'):
lr_clip = tf.clip_by_value(lr,
1 - self._lr_clip_range,
1 + self._lr_clip_range,
name='lr_clip')
surr_clip = lr_clip * adv
obj = tf.minimum(surrogate, surr_clip, name='surr_obj')
obj = tf.boolean_mask(obj, i.valid_var)
# Maximize E[surrogate objective] by minimizing
# -E_t[surrogate objective]
loss = -tf.reduce_mean(obj)
# Encoder entropy bonus
loss -= self.encoder_ent_coeff * encoder_entropy
encoder_mean_kl = self._build_encoder_kl()
# Diagnostic functions
self._f_policy_kl = tf.compat.v1.get_default_session(
).make_callable(pol_mean_kl,
feed_list=flatten_inputs(self._policy_opt_inputs))
self._f_rewards = tf.compat.v1.get_default_session().make_callable(
rewards, feed_list=flatten_inputs(self._policy_opt_inputs))
returns = discounted_returns(self._discount,
self.max_episode_length,
rewards,
name='returns')
self._f_returns = tf.compat.v1.get_default_session().make_callable(
returns, feed_list=flatten_inputs(self._policy_opt_inputs))
return loss, pol_mean_kl, encoder_mean_kl
def _build_policy_loss(self, i):
"""Build policy loss and other output tensors.
Args:
i (namedtuple): Collection of variables to compute policy loss.
Returns:
tf.Tensor: Policy loss.
tf.Tensor: Mean policy KL divergence.
"""
policy_entropy = self._build_entropy_term(i)
rewards = i.reward_var
if self._maximum_entropy:
with tf.name_scope('augmented_rewards'):
rewards = i.reward_var + (self._policy_ent_coeff *
policy_entropy)
with tf.name_scope('policy_loss'):
adv = compute_advantages(self._discount,
self._gae_lambda,
self.max_episode_length,
i.baseline_var,
rewards,
name='adv')
adv = tf.reshape(adv, [-1, self.max_episode_length])
# Optionally normalize advantages
eps = tf.constant(1e-8, dtype=tf.float32)
if self._center_adv:
adv = center_advs(adv, axes=[0], eps=eps)
if self._positive_adv:
adv = positive_advs(adv, eps)
old_policy_dist = self._old_policy_network.dist
policy_dist = self._policy_network.dist
with tf.name_scope('kl'):
kl = old_policy_dist.kl_divergence(policy_dist)
pol_mean_kl = tf.reduce_mean(kl)
# Calculate vanilla loss
with tf.name_scope('vanilla_loss'):
ll = policy_dist.log_prob(i.action_var, name='log_likelihood')
vanilla = ll * adv
# Calculate surrogate loss
with tf.name_scope('surrogate_loss'):
lr = tf.exp(ll - old_policy_dist.log_prob(i.action_var))
surrogate = lr * adv
# Finalize objective function
with tf.name_scope('loss'):
if self._pg_loss == 'vanilla':
# VPG uses the vanilla objective
obj = tf.identity(vanilla, name='vanilla_obj')
elif self._pg_loss == 'surrogate':
# TRPO uses the standard surrogate objective
obj = tf.identity(surrogate, name='surr_obj')
elif self._pg_loss == 'surrogate_clip':
lr_clip = tf.clip_by_value(lr,
1 - self._lr_clip_range,
1 + self._lr_clip_range,
name='lr_clip')
surr_clip = lr_clip * adv
obj = tf.minimum(surrogate, surr_clip, name='surr_obj')
if self._entropy_regularzied:
obj += self._policy_ent_coeff * policy_entropy
# filter only the valid values
obj = tf.boolean_mask(obj, i.valid_var)
# Maximize E[surrogate objective] by minimizing
# -E_t[surrogate objective]
loss = -tf.reduce_mean(obj)
# Diagnostic functions
self._f_policy_kl = tf.compat.v1.get_default_session(
).make_callable(pol_mean_kl,
feed_list=flatten_inputs(self._policy_opt_inputs))
self._f_rewards = tf.compat.v1.get_default_session().make_callable(
rewards, feed_list=flatten_inputs(self._policy_opt_inputs))
returns = discounted_returns(self._discount,
self.max_episode_length, rewards)
self._f_returns = tf.compat.v1.get_default_session().make_callable(
returns, feed_list=flatten_inputs(self._policy_opt_inputs))
return loss, pol_mean_kl