fix RefVariable substraction.

src/TensorFlowNET.Core/Variables/RefVariable.Operators.cs

@@ -14,6 +14,7 @@
    limitations under the License.
 ******************************************************************************/
 
+using System;
 using static Tensorflow.Binding;
 
 namespace Tensorflow
@@ -29,16 +30,29 @@ namespace Tensorflow
         public static Tensor operator -(RefVariable x, double y) => op_helper("sub", x, y);
         public static Tensor operator -(RefVariable x, Tensor y) => op_helper("sub", x, y);
 
-        public static Tensor operator <(RefVariable x, Tensor y) => op_helper("Less", x, y);
+        public static Tensor operator <(RefVariable x, Tensor y) => gen_math_ops.less(x.value(), y);
 
-        public static Tensor operator >(RefVariable x, Tensor y) => op_helper("Greater", x, y);
+        public static Tensor operator >(RefVariable x, Tensor y) => gen_math_ops.greater(x.value(), y);
 
         private static Tensor op_helper<T>(string default_name, RefVariable x, T y)
         {
-            var tensor1 = x.value();
-            return tf_with(ops.name_scope(null, default_name, new { tensor1, y }), scope => {
-                var tensor2 = ops.convert_to_tensor(y, tensor1.dtype.as_base_dtype(), "y");
-                return gen_math_ops.add(tensor1, tensor2, scope);
+            var xVal = x.value();
+            return tf_with(ops.name_scope(null, default_name, new { xVal, y }), scope => {
+                string name = scope;
+                var yTensor = ops.convert_to_tensor(y, xVal.dtype.as_base_dtype(), "y");
+                Tensor result = null;
+                switch (default_name)
+                {
+                    case "add":
+                        result = gen_math_ops.add(xVal, yTensor, name);
+                        break;
+                    case "sub":
+                        result = gen_math_ops.sub(xVal, yTensor, name);
+                        break;
+                    default:
+                        throw new NotImplementedException("");
+                }
+                return result;
             });
         }
     }