Stop gradient when pool_type=='max'

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

@@ -759,6 +759,11 @@ def sequence_pool(input, pool_type, **kwargs):
                  "MaxIndex": max_index},
         attrs={"pooltype": pool_type.upper()})
 
+    # when pool_type is max, variable max_index is initialized,
+    # so we stop the gradient explicitly here
+    if pool_type == 'max':
+        max_index.stop_gradient = True
+
     return pool_out