[GitHub] piiswrong commented on a change in pull request #7067: variational dropout cell

[gi...@git.apache.org]

piiswrong commented on a change in pull request #7067: variational dropout cell
URL: https://github.com/apache/incubator-mxnet/pull/7067#discussion_r130945830
 
 

 ##########
 File path: python/mxnet/gluon/rnn/rnn_cell.py
 ##########
 @@ -719,6 +719,68 @@ def unroll(self, length, inputs, begin_state=None, layout='NTC', merge_outputs=N
         return outputs, states
 
 
+class VariationalDropoutCell(ModifierCell):
+    """
+    Applies Variational Dropout on base cell.
+    (https://arxiv.org/pdf/1512.05287.pdf,
+     https://www.stat.berkeley.edu/~tsmoon/files/Conference/asru2015.pdf).
+    """
+    def __init__(self, base_cell, vardrop_inputs=0., vardrop_outputs=0., vardrop_states=0.):
+        assert not isinstance(base_cell, BidirectionalCell), \
+            "BidirectionalCell doesn't support vardrop since it doesn't support step. " \
+            "Please add VariationalDropoutCell to the cells underneath instead."
+        assert not isinstance(base_cell, SequentialRNNCell) or not base_cell._bidirectional, \
+            "Bidirectional SequentialRNNCell doesn't support vardrop. " \
+            "Please add VariationalDropoutCell to the cells underneath instead."
+        super(VariationalDropoutCell, self).__init__(base_cell)
+        self.vardrop_inputs = vardrop_inputs
+        self.vardrop_states = vardrop_states
+        self.vardrop_outputs = vardrop_outputs
+        self.vardrop_inputs_mask = None
+        self.vardrop_states_mask = None
+        self.vardrop_outputs_mask = None
+
+    def _alias(self):
+        return 'vardrop'
+
+    def reset(self):
+        super(VariationalDropoutCell, self).reset()
+        self.vardrop_inputs_mask = None
+        self.vardrop_states_mask = None
+        self.vardrop_outputs_mask = None
+
+    def hybrid_forward(self, F, inputs, states):
+        cell = self.base_cell
+
+        if self.vardrop_states:
+            if self.vardrop_states_mask is None:
+                self.vardrop_states_mask = F.Dropout(F.ones_like(states[0]),
+                                                     p=self.vardrop_states)
+            states = list(states)
+            states[0] = states[0] * self.vardrop_states_mask
 
 Review comment:
   there can be multiple states
 
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