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