modify epsilon greedy exploration to add epsilon scheduling

Summary: Our current epsilon-greedy exploration module does not allow annealing epsilon. Add this.

Reviewed By: rodrigodesalvobraz

Differential Revision: D65923616

fbshipit-source-id: b3e280010e2adae22a6b428abc9e6e1af42cc0dc

pearl/policy_learners/exploration_modules/common/epsilon_greedy_exploration.py

@@ -26,9 +26,28 @@ class EGreedyExploration(UniformExplorationBase):
     epsilon Greedy exploration module.
     """
 
-    def __init__(self, epsilon: float) -> None:
+    def __init__(
+        self,
+        epsilon: float,
+        start_epsilon: Optional[float] = None,
+        end_epsilon: Optional[float] = None,
+        warmup_steps: Optional[int] = None,
+    ) -> None:
         super().__init__()
-        self.epsilon = epsilon
+        self.start_epsilon = start_epsilon
+        self.end_epsilon = end_epsilon
+        self.warmup_steps = warmup_steps
+        self.time_step = 0
+        self._epsilon_scheduling: bool = (
+            self.start_epsilon is not None
+            and self.end_epsilon is not None
+            and self.warmup_steps is not None
+        )
+        if self._epsilon_scheduling:
+            assert self.start_epsilon is not None
+            self.curr_epsilon: float = self.start_epsilon
+        else:
+            self.curr_epsilon = epsilon
 
     def act(
         self,
@@ -39,13 +58,24 @@ def act(
         action_availability_mask: torch.Tensor | None = None,
         representation: torch.nn.Module | None = None,
     ) -> Action:
+        if self._epsilon_scheduling:
+            assert self.warmup_steps is not None
+            if self.time_step < self.warmup_steps:
+                assert self.warmup_steps is not None
+                frac = self.time_step / self.warmup_steps
+                assert self.start_epsilon is not None
+                assert self.end_epsilon is not None
+                self.curr_epsilon = (
+                    self.start_epsilon + (self.end_epsilon - self.start_epsilon) * frac
+                )
+        self.time_step += 1
         if exploit_action is None:
             raise ValueError(
                 "exploit_action cannot be None for epsilon-greedy exploration"
             )
         if not isinstance(action_space, DiscreteActionSpace):
             raise TypeError("action space must be discrete")
-        if random.random() < self.epsilon:
+        if random.random() < self.curr_epsilon:
             return action_space.sample(action_availability_mask).to(
                 exploit_action.device
             )

pearl/policy_learners/sequential_decision_making/tabular_q_learning.py

@@ -209,7 +209,7 @@ def __str__(self) -> str:
         assert isinstance(exploration_module, EGreedyExploration)
         items = [
             "α=" + str(self.learning_rate),
-            "ε=" + str(exploration_module.epsilon),
+            "ε=" + str(exploration_module.curr_epsilon),
             "λ=" + str(self.discount_factor),
         ]
         return "Q-Learning" + (