[BugFix] solve PDP tour issues #231

rl4co/envs/routing/pdp/env.py

@@ -42,6 +42,9 @@ class PDPEnv(RL4COEnvBase):
     Args:
         generator: PDPGenerator instance as the data generator
         generator_params: parameters for the generator
+        force_start_at_depot: whether to force the agent to start at the depot
+            If False (default), the agent won't consider the depot, which is added in the `get_reward` method
+            If True, the only valid action at the first step is to visit the depot (=0)
     """
 
     name = "pdp"
@@ -50,12 +53,14 @@ def __init__(
         self,
         generator: PDPGenerator = None,
         generator_params: dict = {},
+        force_start_at_depot: bool = False,
         **kwargs,
     ):
         super().__init__(**kwargs)
         if generator is None:
             generator = PDPGenerator(**generator_params)
         self.generator = generator
+        self.force_start_at_depot = force_start_at_depot
         self._make_spec(self.generator)
 
     @staticmethod
@@ -85,7 +90,7 @@ def _step(td: TensorDict) -> TensorDict:
 
         # The reward is calculated outside via get_reward for efficiency, so we set it to 0 here
         reward = torch.zeros_like(done)
-
+        
         # Update step
         td.update(
             {
@@ -122,12 +127,17 @@ def _reset(self, td: Optional[TensorDict] = None, batch_size=None) -> TensorDict
             dim=-1,
         )
 
-        # Cannot visit depot at first step # [0,1...1] so set not available
+        # Masking variables
         available = torch.ones(
             (*batch_size, self.generator.num_loc + 1), dtype=torch.bool
         ).to(device)
-        action_mask = ~available.contiguous()  # [batch_size, graph_size+1]
-        action_mask[..., 0] = 1  # First step is always the depot
+        action_mask = torch.ones_like(available) # [batch_size, graph_size+1]
+        if self.force_start_at_depot:
+            action_mask[..., 1:] = False # can only visit the depot at the first step
+        else:
+            action_mask = action_mask & to_deliver
+            available[..., 0] = False # depot is already visited (during reward calculation)
+            action_mask[..., 0] = False # depot is not available to visit
 
         # Other variables
         current_node = torch.zeros((*batch_size, 1), dtype=torch.int64).to(device)
@@ -194,13 +204,18 @@ def _get_reward(td, actions) -> TensorDict:
         return -get_tour_length(locs_ordered)
 
     def check_solution_validity(self, td, actions):
-        # assert (actions[:, 0] == 0).all(), "Not starting at depot"
+        if not self.force_start_at_depot:
+            actions = torch.cat((torch.zeros_like(actions[:, 0:1]), actions), dim=-1)
+
         assert (
-            torch.arange(actions.size(1), out=actions.data.new())
+            (torch.arange(actions.size(1), out=actions.data.new()))
             .view(1, -1)
             .expand_as(actions)
             == actions.data.sort(1)[0]
         ).all(), "Not visiting all nodes"
+
+        # make sure we don't go back to the depot in the middle of the tour
+        assert (actions[:, 1:-1] != 0).all(), "Going back to depot in the middle of the tour (not allowed)"
 
         visited_time = torch.argsort(
             actions, 1