set stop gradient for mask in dropout layer (#7390)

Author: QiJune

python/paddle/v2/fluid/layers/nn.py

@@ -14,7 +14,7 @@
     'chunk_eval', 'sequence_conv', 'conv2d', 'sequence_pool', 'pool2d',
     'batch_norm', 'beam_search_decode', 'conv2d_transpose', 'sequence_expand',
     'lstm_unit', 'reduce_sum', 'reduce_mean', 'reduce_max', 'reduce_min',
-    'sequence_first_step', 'sequence_last_step'
+    'sequence_first_step', 'sequence_last_step', 'dropout'
 ]
 
 
@@ -386,6 +386,21 @@ def cos_sim(X, Y, **kwargs):
     return out
 
 
+def dropout(x, dropout_prob, is_test=False, seed=0, **kwargs):
+    helper = LayerHelper('dropout', **kwargs)
+    out = helper.create_tmp_variable(dtype=x.dtype)
+    mask = helper.create_tmp_variable(dtype=x.dtype, stop_gradient=True)
+    helper.append_op(
+        type='dropout',
+        inputs={'X': [x]},
+        outputs={'Out': [out],
+                 'Mask': [mask]},
+        attrs={'dropout_prob': dropout_prob,
+               'is_test': is_test,
+               'seed': seed})
+    return out
+
+
 def cross_entropy(input, label, **kwargs):
     """
     **Cross Entropy Layer**

python/paddle/v2/fluid/layers/ops.py

@@ -1,23 +1,12 @@
 from ..registry import register_layer
 
 __activations__ = [
-    'abs',
-    'ceil',
-    'exp',
-    'floor',
-    'log',
-    'relu',
-    'round',
-    'sigmoid',
-    'sqrt',
-    'square',
-    'tanh',
+    'abs', 'tanh', 'sigmoid', 'relu', 'sqrt', 'ceil', 'floor', 'log', 'round'
 ]
 
 __all__ = [
     'mean',
     'mul',
-    'dropout',
     'reshape',
     'scale',
     'transpose',