diff --git a/src/TensorFlowNET.Core/APIs/tf.math.cs b/src/TensorFlowNET.Core/APIs/tf.math.cs
index 5d74a4df..9c283bbf 100644
--- a/src/TensorFlowNET.Core/APIs/tf.math.cs
+++ b/src/TensorFlowNET.Core/APIs/tf.math.cs
@@ -35,13 +35,25 @@ namespace Tensorflow
         public static Tensor reduce_sum(Tensor input, int[] axis = null)
         {
             Tensor rank;
+            string name;
             using (var namescop = new ops.name_scope<Tensor>("", "Rank", new List<Tensor> { input }))
             {
-                string name = namescop;
-                rank = gen_array_ops.rank(input, name);
+                name = namescop;
+                rank = gen_array_ops.rank(input, namescop);
             }
+
+            using (var namescope = new ops.name_scope<Tensor>("range", "Range", new List<Tensor> { 0D, input, 1D }))
+            {
+                name = namescope;
+                var start = ops.convert_to_tensor(0D);
+                var limit = ops.convert_to_tensor(input);
+                var delta = ops.convert_to_tensor(1D);
+
+                var t = gen_math_ops.range(start, limit, delta, name);
+            }
+                
             var s = gen_math_ops.sum(input, rank);
-            return gen_math_ops.range(0, s);
+            return s;
         }
     }
 }
diff --git a/src/TensorFlowNET.Core/Gradients/gradients_impl.py.cs b/src/TensorFlowNET.Core/Gradients/gradients_impl.py.cs
index edcbd33f..597c4e21 100644
--- a/src/TensorFlowNET.Core/Gradients/gradients_impl.py.cs
+++ b/src/TensorFlowNET.Core/Gradients/gradients_impl.py.cs
@@ -57,6 +57,8 @@ namespace Tensorflow
                 // cluster ops for compilation.
                 var gradient_uid = ops.get_default_graph().unique_name("uid");
 
+                // Initialize the pending count for ops in the connected subgraph from ys
+                // to the xs.
                 var to_ops = ys1.Select(x => x.op).ToList();
                 var from_ops = xs1.Select(x => x.op).ToList();
                 var stop_gradient_ops = stop_gradients1.Select(x => x.op).ToList();
diff --git a/src/TensorFlowNET.Core/Operations/Operation.cs b/src/TensorFlowNET.Core/Operations/Operation.cs
index aad9c555..783a8ef7 100644
--- a/src/TensorFlowNET.Core/Operations/Operation.cs
+++ b/src/TensorFlowNET.Core/Operations/Operation.cs
@@ -163,7 +163,7 @@ namespace Tensorflow
 
         public override string ToString()
         {
-            return $"'{Name}' type={OpType}";
+            return _handle == IntPtr.Zero ? "Undefined" : $"'{Name}' type={OpType}";
         }
 
         public static implicit operator Operation(IntPtr handle) => new Operation(handle);
diff --git a/src/TensorFlowNET.Core/Operations/gen_math_ops.cs b/src/TensorFlowNET.Core/Operations/gen_math_ops.cs
index 91e7e629..8767d5ea 100644
--- a/src/TensorFlowNET.Core/Operations/gen_math_ops.cs
+++ b/src/TensorFlowNET.Core/Operations/gen_math_ops.cs
@@ -98,23 +98,16 @@ namespace Tensorflow
         /// <param name="delta"></param>
         /// <param name="name"></param>
         /// <returns></returns>
-        public static Tensor range(int start, Tensor limit, int delta = 1)
+        public static Tensor range(Tensor start, Tensor limit, Tensor delta, string name = "")
         {
-            using (var namescope = new ops.name_scope<Tensor>("", "Range", new List<Tensor> { start, limit, delta }))
-            {
-                var start1 = ops.convert_to_tensor(start, "start");
-                var limit1 = ops.convert_to_tensor(limit, "limit");
-                var delta1 = ops.convert_to_tensor(delta, "delta");
-
-                var keywords = new Dictionary<string, object>();
-                keywords.Add("start", start1);
-                keywords.Add("limit", limit1);
-                keywords.Add("delta", delta1);
+            var keywords = new Dictionary<string, object>();
+            keywords.Add("start", start);
+            keywords.Add("limit", limit);
+            keywords.Add("delta", delta);
 
-                var _op = _op_def_lib._apply_op_helper("Range", namescope, keywords);
+            var _op = _op_def_lib._apply_op_helper("Range", name, keywords);
 
-                return _op.outputs[0];
-            }
+            return _op.outputs[0];
         }
     }
 }
diff --git a/src/TensorFlowNET.Core/Variables/RefVariable.cs b/src/TensorFlowNET.Core/Variables/RefVariable.cs
index 01a354f0..aa02b5f3 100644
--- a/src/TensorFlowNET.Core/Variables/RefVariable.cs
+++ b/src/TensorFlowNET.Core/Variables/RefVariable.cs
@@ -91,9 +91,6 @@ namespace Tensorflow
                     _snapshot = gen_array_ops.identity(_variable, name = "read");
                 }
 
-                // clear g._name_stack
-                ops.get_default_graph().old_stack = "";
-
                 ops.add_to_collections(collections, this);
             }
         }
diff --git a/src/TensorFlowNET.Core/ops.name_scope.cs b/src/TensorFlowNET.Core/ops.name_scope.cs
index 3c7c124e..26b5e114 100644
--- a/src/TensorFlowNET.Core/ops.name_scope.cs
+++ b/src/TensorFlowNET.Core/ops.name_scope.cs
@@ -46,6 +46,8 @@ namespace Tensorflow
             {
                 var g = get_default_graph();
                 g._name_stack = g.old_stack;
+                // clear g._name_stack
+                g.old_stack = "";
             }
 
             /// <summary>
@@ -54,7 +56,10 @@ namespace Tensorflow
             /// <param name="ns"></param>
             public static implicit operator string(name_scope<T> ns)
             {
-                return ns.__enter__();
+                if (string.IsNullOrEmpty(ns._name_scope))
+                    return ns.__enter__();
+                else
+                    return ns._name_scope;
             }
         }
     }
diff --git a/src/TensorFlowNET.Core/ops.py.cs b/src/TensorFlowNET.Core/ops.py.cs
index 3cc5d18f..feda8bb6 100644
--- a/src/TensorFlowNET.Core/ops.py.cs
+++ b/src/TensorFlowNET.Core/ops.py.cs
@@ -47,8 +47,14 @@ namespace Tensorflow
 
         public static Tensor convert_to_tensor(object value, string name = "")
         {
-            var nd = tensor_util.convert_to_numpy_ndarray(value);
-            return tf.constant(nd, name);
+            switch (value)
+            {
+                case Tensor val:
+                    return val;
+                default:
+                    var nd = tensor_util.convert_to_numpy_ndarray(value);
+                    return tf.constant(nd, name);
+            }
         }
 
         public static unsafe IntPtr _create_c_op(Graph graph, NodeDef node_def, List<Tensor> inputs)
@@ -90,7 +96,7 @@ namespace Tensorflow
 
             var c_op = c_api.TF_FinishOperation(op_desc, status);
 
-            if (status.Code != TF_Code.TF_OK) throw new Exception(status.Message);
+            status.Check(true);
 
             return c_op;
         }