fix a bug of sub() in layer_math.py

python/paddle/trainer_config_helpers/layer_math.py

@@ -75,7 +75,7 @@ LayerOutput.__add__ = add
 
 def sub(layeroutput, other):
     if is_compatible_with(other, float):
-        return slope_intercept_layer(input=layeroutput, intercept=other)
+        return slope_intercept_layer(input=layeroutput, intercept=-other)
     if not isinstance(other, LayerOutput):
         logger.fatal("LayerOutput can only be subtracted with"
                      " another Layeroutput or a number")

python/paddle/trainer_config_helpers/tests/configs/protostr/math_ops.protostr

@@ -230,7 +230,7 @@ layers {
     input_layer_name: "__mixed_1__"
   }
   slope: 1.0
-  intercept: 2
+  intercept: -2
 }
 layers {
   name: "__slope_intercept_layer_4__"
@@ -411,4 +411,3 @@ sub_models {
   output_layer_names: "__mixed_3__"
   is_recurrent_layer_group: false
 }
-