Add location sensitive attention

layers/attention.py

@@ -29,34 +29,50 @@ class BahdanauAttention(nn.Module):
 
         # (batch, max_time)
         return alignment.squeeze(-1)
-
-
-def get_mask_from_lengths(inputs, inputs_lengths):
-    """Get mask tensor from list of length
-
-    Args:
-        inputs: Tensor in size (batch, max_time, dim)
-        inputs_lengths: array like
-    """
-    mask = inputs.data.new(inputs.size(0), inputs.size(1)).byte().zero_()
-    for idx, l in enumerate(inputs_lengths):
-        mask[idx][:l] = 1
-    return ~mask
+    
+    
+class LocationSensitiveAttention(nn.Module):
+    """Location sensitive attention following
+    https://arxiv.org/pdf/1506.07503.pdf"""
+    def __init__(self, annot_dim, out_dim, hidden_dim):
+        loc_kernel_size = 31
+        loc_dim = 32
+        padding = int((loc_kernel_size -1) / 2)
+        self.loc_conv =  nn.Conv1d(2, loc_dim,
+                                   kernel_size=loc_kernel_size, stride=1,
+                                   padding=padding, bias=False)
+        self.loc_linear = nn.Linear(loc_dim, hidden_dim)
+        self.query_layer = nn.Linear(query_dim, hidden_dim, bias=True)
+        self.annot_layer = nn.Linear(annot_dim, hidden_dim, bias=True)
+        self.v = nn.Linear(hidden_dim, 1, bias=False)
+        
+    def forward(self, query, annot, loc):
+        """
+        Shapes:
+            - query: (batch, 1, dim) or (batch, dim)
+            - annots: (batch, max_time, dim)
+            - loc: (batch, 2, max_time)
+        """
+        loc_conv = self.loc_conv(loc)
+        loc_conv = loc_conv.transpose(1, 2)
+        processed_loc = self.loc_linear(loc_conv)
+        processed_query = self.query_layer(query)
+        processed_annots = self.annot_layer(annot)
+        alignment = self.v(nn.functional.tanh(
+            processed_query + processed_annots + processed_loc))
+        # (batch, max_time)
+        return alignment.squeeze(-1)
 
 
 class AttentionRNN(nn.Module):
-    def __init__(self, out_dim, annot_dim, memory_dim,
-                 score_mask_value=-float("inf")):
+    def __init__(self, out_dim, annot_dim, memory_dim):
         super(AttentionRNN, self).__init__()
         self.rnn_cell = nn.GRUCell(out_dim + memory_dim, out_dim)
-        self.alignment_model = BahdanauAttention(annot_dim, out_dim, out_dim)
+        self.alignment_model = LocationSensitiveAttention(annot_dim, out_dim, out_dim, 3, out_dim)
         self.score_mask_value = score_mask_value
 
     def forward(self, memory, context, rnn_state, annotations,
-                mask=None, annotations_lengths=None):
-
-        if annotations_lengths is not None and mask is None:
-            mask = get_mask_from_lengths(annotations, annotations_lengths)
+                attention_vec, mask=None, annotations_lengths=None):
 
         # Concat input query and previous context context
         rnn_input = torch.cat((memory, context), -1)
@@ -85,3 +101,4 @@ class AttentionRNN(nn.Module):
         context = torch.bmm(alignment.unsqueeze(1), annotations)
         context = context.squeeze(1)
         return rnn_output, context, alignment
+