change hlactivetype instead of act.name

Author: Haonan

paddle/utils/Util.cpp

@@ -378,7 +378,7 @@ hl_activation_mode_t hlActiveType(const std::string& type) {
     return HL_ACTIVATION_RELU;
   } else if (type == "tanh") {
     return HL_ACTIVATION_TANH;
-  } else if (type == "linear") {
+  } else if (type == "linear" || type == "") {
     return HL_ACTIVATION_LINEAR;
   } else {
     LOG(FATAL) << "Do not support activation type " << type;

python/paddle/trainer_config_helpers/activations.py

@@ -104,7 +104,7 @@ class IdentityActivation(BaseActivation):
     Just do nothing for output both forward/backward.
     """
 
-    def __init__(self): BaseActivation.__init__(self, 'linear', False)
+    def __init__(self): BaseActivation.__init__(self, '', False)
 
 
 LinearActivation = IdentityActivation