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from typing import Dict, cast
from mlagents.torch_utils import torch
from mlagents.trainers.buffer import AgentBuffer
from mlagents_envs.timers import timed
from mlagents.trainers.policy.torch_policy import TorchPolicy
from mlagents.trainers.optimizer.torch_optimizer import TorchOptimizer
from mlagents.trainers.settings import TrainerSettings, PPOSettings
from mlagents.trainers.torch.agent_action import AgentAction
from mlagents.trainers.torch.action_log_probs import ActionLogProbs
from mlagents.trainers.torch.utils import ModelUtils
from mlagents.trainers.trajectory import ObsUtil
class TorchPPOOptimizer(TorchOptimizer):
def __init__(self, policy: TorchPolicy, trainer_settings: TrainerSettings):
"""
Takes a Policy and a Dict of trainer parameters and creates an Optimizer around the policy.
The PPO optimizer has a value estimator and a loss function.
:param policy: A TorchPolicy object that will be updated by this PPO Optimizer.
:param trainer_params: Trainer parameters dictionary that specifies the
properties of the trainer.
"""
# Create the graph here to give more granular control of the TF graph to the Optimizer.
super().__init__(policy, trainer_settings)
params = list(self.policy.actor_critic.parameters())
self.hyperparameters: PPOSettings = cast(
PPOSettings, trainer_settings.hyperparameters
)
self.decay_learning_rate = ModelUtils.DecayedValue(
self.hyperparameters.learning_rate_schedule,
self.hyperparameters.learning_rate,
1e-10,
self.trainer_settings.max_steps,
)
self.decay_epsilon = ModelUtils.DecayedValue(
self.hyperparameters.learning_rate_schedule,
self.hyperparameters.epsilon,
0.1,
self.trainer_settings.max_steps,
)
self.decay_beta = ModelUtils.DecayedValue(
self.hyperparameters.learning_rate_schedule,
self.hyperparameters.beta,
1e-5,
self.trainer_settings.max_steps,
)
self.optimizer = torch.optim.Adam(
params, lr=self.trainer_settings.hyperparameters.learning_rate
)
self.stats_name_to_update_name = {
"Losses/Value Loss": "value_loss",
"Losses/Policy Loss": "policy_loss",
}
self.stream_names = list(self.reward_signals.keys())
def ppo_value_loss(
self,
values: Dict[str, torch.Tensor],
old_values: Dict[str, torch.Tensor],
returns: Dict[str, torch.Tensor],
epsilon: float,
loss_masks: torch.Tensor,
) -> torch.Tensor:
"""
Evaluates value loss for PPO.
:param values: Value output of the current network.
:param old_values: Value stored with experiences in buffer.
:param returns: Computed returns.
:param epsilon: Clipping value for value estimate.
:param loss_mask: Mask for losses. Used with LSTM to ignore 0'ed out experiences.
"""
value_losses = []
for name, head in values.items():
old_val_tensor = old_values[name]
returns_tensor = returns[name]
clipped_value_estimate = old_val_tensor + torch.clamp(
head - old_val_tensor, -1 * epsilon, epsilon
)
v_opt_a = (returns_tensor - head) ** 2
v_opt_b = (returns_tensor - clipped_value_estimate) ** 2
value_loss = ModelUtils.masked_mean(torch.max(v_opt_a, v_opt_b), loss_masks)
value_losses.append(value_loss)
value_loss = torch.mean(torch.stack(value_losses))
return value_loss
def ppo_policy_loss(
self,
advantages: torch.Tensor,
log_probs: torch.Tensor,
old_log_probs: torch.Tensor,
loss_masks: torch.Tensor,
) -> torch.Tensor:
"""
Evaluate PPO policy loss.
:param advantages: Computed advantages.
:param log_probs: Current policy probabilities
:param old_log_probs: Past policy probabilities
:param loss_masks: Mask for losses. Used with LSTM to ignore 0'ed out experiences.
"""
advantage = advantages.unsqueeze(-1)
decay_epsilon = self.hyperparameters.epsilon
r_theta = torch.exp(log_probs - old_log_probs)
p_opt_a = r_theta * advantage
p_opt_b = (
torch.clamp(r_theta, 1.0 - decay_epsilon, 1.0 + decay_epsilon) * advantage
)
policy_loss = -1 * ModelUtils.masked_mean(
torch.min(p_opt_a, p_opt_b), loss_masks
)
return policy_loss
@timed
def update(self, batch: AgentBuffer, num_sequences: int) -> Dict[str, float]:
"""
Performs update on model.
:param batch: Batch of experiences.
:param num_sequences: Number of sequences to process.
:return: Results of update.
"""
# Get decayed parameters
decay_lr = self.decay_learning_rate.get_value(self.policy.get_current_step())
decay_eps = self.decay_epsilon.get_value(self.policy.get_current_step())
decay_bet = self.decay_beta.get_value(self.policy.get_current_step())
returns = {}
old_values = {}
for name in self.reward_signals:
old_values[name] = ModelUtils.list_to_tensor(
batch[f"{name}_value_estimates"]
)
returns[name] = ModelUtils.list_to_tensor(batch[f"{name}_returns"])
n_obs = len(self.policy.behavior_spec.observation_specs)
current_obs = ObsUtil.from_buffer(batch, n_obs)
# Convert to tensors
current_obs = [ModelUtils.list_to_tensor(obs) for obs in current_obs]
act_masks = ModelUtils.list_to_tensor(batch["action_mask"])
actions = AgentAction.from_dict(batch)
memories = [
ModelUtils.list_to_tensor(batch["memory"][i])
for i in range(0, len(batch["memory"]), self.policy.sequence_length)
]
if len(memories) > 0:
memories = torch.stack(memories).unsqueeze(0)
log_probs, entropy, values = self.policy.evaluate_actions(
current_obs,
masks=act_masks,
actions=actions,
memories=memories,
seq_len=self.policy.sequence_length,
)
old_log_probs = ActionLogProbs.from_dict(batch).flatten()
log_probs = log_probs.flatten()
loss_masks = ModelUtils.list_to_tensor(batch["masks"], dtype=torch.bool)
value_loss = self.ppo_value_loss(
values, old_values, returns, decay_eps, loss_masks
)
policy_loss = self.ppo_policy_loss(
ModelUtils.list_to_tensor(batch["advantages"]),
log_probs,
old_log_probs,
loss_masks,
)
loss = (
policy_loss
+ 0.5 * value_loss
- decay_bet * ModelUtils.masked_mean(entropy, loss_masks)
)
# Set optimizer learning rate
ModelUtils.update_learning_rate(self.optimizer, decay_lr)
self.optimizer.zero_grad()
loss.backward()
self.optimizer.step()
update_stats = {
# NOTE: abs() is not technically correct, but matches the behavior in TensorFlow.
# TODO: After PyTorch is default, change to something more correct.
"Losses/Policy Loss": torch.abs(policy_loss).item(),
"Losses/Value Loss": value_loss.item(),
"Policy/Learning Rate": decay_lr,
"Policy/Epsilon": decay_eps,
"Policy/Beta": decay_bet,
}
for reward_provider in self.reward_signals.values():
update_stats.update(reward_provider.update(batch))
return update_stats
def get_modules(self):
modules = {"Optimizer": self.optimizer}
for reward_provider in self.reward_signals.values():
modules.update(reward_provider.get_modules())
return modules