[add-fire] Add learning rate and beta/epsilon decay to PyTorch (#4318)

ml-agents/mlagents/trainers/ppo/optimizer_torch.py

         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.stream_names = list(self.reward_signals.keys())
 
-    def ppo_value_loss(self, values, old_values, returns):
+    def ppo_value_loss(
+        self,
+        values: Dict[str, torch.Tensor],
+        old_values: Dict[str, torch.Tensor],
+        returns: Dict[str, torch.Tensor],
+        epsilon: float,
+    ) -> torch.Tensor:
         """
         Creates training-specific Tensorflow ops for PPO models.
         :param returns:
-
-        decay_epsilon = self.hyperparameters.epsilon
-
-                head - old_val_tensor, -decay_epsilon, decay_epsilon
+                head - old_val_tensor, -1 * epsilon, epsilon
             )
             v_opt_a = (returns_tensor - head) ** 2
             v_opt_b = (returns_tensor - clipped_value_estimate) ** 2
         :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:
             memories=memories,
             seq_len=self.policy.sequence_length,
         )
-        value_loss = self.ppo_value_loss(values, old_values, returns)
+        value_loss = self.ppo_value_loss(values, old_values, returns, decay_eps)
         policy_loss = self.ppo_policy_loss(
             ModelUtils.list_to_tensor(batch["advantages"]),
             log_probs,
-        loss = (
-            policy_loss
-            + 0.5 * value_loss
-            - self.hyperparameters.beta * torch.mean(entropy)
-        )
+        loss = policy_loss + 0.5 * value_loss - decay_bet * torch.mean(entropy)
+
+        # Set optimizer learning rate
+        ModelUtils.update_learning_rate(self.optimizer, decay_lr)
         self.optimizer.zero_grad()
         loss.backward()
 
             "Losses/Value Loss": value_loss.detach().cpu().numpy(),
+            "Policy/Learning Rate": decay_lr,
+            "Policy/Epsilon": decay_eps,
+            "Policy/Beta": decay_bet,
         }
 
         return update_stats

ml-agents/mlagents/trainers/sac/optimizer_torch.py

     def __init__(self, policy: TorchPolicy, trainer_params: TrainerSettings):
         super().__init__(policy, trainer_params)
         hyperparameters: SACSettings = cast(SACSettings, trainer_params.hyperparameters)
-        lr = hyperparameters.learning_rate
-        # lr_schedule = hyperparameters.learning_rate_schedule
-        # max_step = trainer_params.max_steps
         self.tau = hyperparameters.tau
         self.init_entcoef = hyperparameters.init_entcoef
 
-        # h_size = policy_network_settings.hidden_units
-        # num_layers = policy_network_settings.num_layers
-        # vis_encode_type = policy_network_settings.vis_encode_type
 
         self.tau = hyperparameters.tau
         self.burn_in_ratio = 0.0
         for param in policy_params:
             logger.debug(param.shape)
 
-        self.policy_optimizer = torch.optim.Adam(policy_params, lr=lr)
-        self.value_optimizer = torch.optim.Adam(value_params, lr=lr)
-        self.entropy_optimizer = torch.optim.Adam([self._log_ent_coef], lr=lr)
+        self.decay_learning_rate = ModelUtils.DecayedValue(
+            hyperparameters.learning_rate_schedule,
+            hyperparameters.learning_rate,
+            1e-10,
+            self.trainer_settings.max_steps,
+        )
+        self.policy_optimizer = torch.optim.Adam(
+            policy_params, lr=hyperparameters.learning_rate
+        )
+        self.value_optimizer = torch.optim.Adam(
+            value_params, lr=hyperparameters.learning_rate
+        )
+        self.entropy_optimizer = torch.optim.Adam(
+            [self._log_ent_coef], lr=hyperparameters.learning_rate
+        )
 
     def sac_q_loss(
         self,
 
         total_value_loss = q1_loss + q2_loss + value_loss
 
+        decay_lr = self.decay_learning_rate.get_value(self.policy.get_current_step())
+        ModelUtils.update_learning_rate(self.policy_optimizer, decay_lr)
+        ModelUtils.update_learning_rate(self.value_optimizer, decay_lr)
+        ModelUtils.update_learning_rate(self.entropy_optimizer, decay_lr)
         self.entropy_optimizer.zero_grad()
         entropy_loss.backward()
         self.entropy_optimizer.step()
             .detach()
             .cpu()
             .numpy(),
+            "Policy/Learning Rate": decay_lr,
         }
 
         return update_stats

ml-agents/mlagents/trainers/tests/torch/test_utils.py

 import torch
 import numpy as np
 
-from mlagents.trainers.settings import EncoderType
+from mlagents.trainers.settings import EncoderType, ScheduleType
 from mlagents.trainers.torch.utils import ModelUtils
 from mlagents.trainers.exception import UnityTrainerException
 from mlagents.trainers.torch.encoders import (
 
     for enc in vis_enc:
         assert isinstance(enc, ModelUtils.get_encoder_for_type(encoder_type))
+
+
+def test_decayed_value():
+    test_steps = [0, 4, 9]
+    # Test constant decay
+    param = ModelUtils.DecayedValue(ScheduleType.CONSTANT, 1.0, 0.2, test_steps[-1])
+    for _step in test_steps:
+        _param = param.get_value(_step)
+        assert _param == 1.0
+
+    test_results = [1.0, 0.6444, 0.2]
+    # Test linear decay
+    param = ModelUtils.DecayedValue(ScheduleType.LINEAR, 1.0, 0.2, test_steps[-1])
+    for _step, _result in zip(test_steps, test_results):
+        _param = param.get_value(_step)
+        assert _param == pytest.approx(_result, abs=0.01)
+
+    # Test invalid
+    with pytest.raises(UnityTrainerException):
+        ModelUtils.DecayedValue(
+            "SomeOtherSchedule", 1.0, 0.2, test_steps[-1]
+        ).get_value(0)
+
+
+def test_polynomial_decay():
+    test_steps = [0, 4, 9]
+    test_results = [1.0, 0.7, 0.2]
+    for _step, _result in zip(test_steps, test_results):
+        decayed = ModelUtils.polynomial_decay(
+            1.0, 0.2, test_steps[-1], _step, power=0.8
+        )
+        assert decayed == pytest.approx(_result, abs=0.01)
 
 
 def test_list_to_tensor():

ml-agents/mlagents/trainers/torch/utils.py

     VectorEncoder,
     VectorAndUnnormalizedInputEncoder,
 )
-from mlagents.trainers.settings import EncoderType
+from mlagents.trainers.settings import EncoderType, ScheduleType
 from mlagents.trainers.exception import UnityTrainerException
 from mlagents.trainers.torch.distributions import DistInstance, DiscreteDistInstance
 
     def swish(input_activation: torch.Tensor) -> torch.Tensor:
         """Swish activation function. For more info: https://arxiv.org/abs/1710.05941"""
         return torch.mul(input_activation, torch.sigmoid(input_activation))
+
+    @staticmethod
+    def update_learning_rate(optim: torch.optim.Optimizer, lr: float) -> None:
+        """
+        Apply a learning rate to a torch optimizer.
+        :param optim: Optimizer
+        :param lr: Learning rate
+        """
+        for param_group in optim.param_groups:
+            param_group["lr"] = lr
+
+    class DecayedValue:
+        def __init__(
+            self,
+            schedule: ScheduleType,
+            initial_value: float,
+            min_value: float,
+            max_step: int,
+        ):
+            """
+            Object that represnets value of a parameter that should be decayed, assuming it is a function of
+            global_step.
+            :param schedule: Type of learning rate schedule.
+            :param initial_value: Initial value before decay.
+            :param min_value: Decay value to this value by max_step.
+            :param max_step: The final step count where the return value should equal min_value.
+            :param global_step: The current step count.
+            :return: The value.
+            """
+            self.schedule = schedule
+            self.initial_value = initial_value
+            self.min_value = min_value
+            self.max_step = max_step
+
+        def get_value(self, global_step: int) -> float:
+            """
+            Get the value at a given global step.
+            :param global_step: Step count.
+            :returns: Decayed value at this global step.
+            """
+            if self.schedule == ScheduleType.CONSTANT:
+                return self.initial_value
+            elif self.schedule == ScheduleType.LINEAR:
+                return ModelUtils.polynomial_decay(
+                    self.initial_value, self.min_value, self.max_step, global_step
+                )
+            else:
+                raise UnityTrainerException(f"The schedule {self.schedule} is invalid.")
+
+    @staticmethod
+    def polynomial_decay(
+        initial_value: float,
+        min_value: float,
+        max_step: int,
+        global_step: int,
+        power: float = 1.0,
+    ) -> float:
+        """
+        Get a decayed value based on a polynomial schedule, with respect to the current global step.
+        :param initial_value: Initial value before decay.
+        :param min_value: Decay value to this value by max_step.
+        :param max_step: The final step count where the return value should equal min_value.
+        :param global_step: The current step count.
+        :param power: Power of polynomial decay. 1.0 (default) is a linear decay.
+        :return: The current decayed value.
+        """
+        global_step = min(global_step, max_step)
+        decayed_value = (initial_value - min_value) * (
+            1 - float(global_step) / max_step
+        ) ** (power) + min_value
+        return decayed_value
 
     @staticmethod
     def get_encoder_for_type(encoder_type: EncoderType) -> nn.Module: