diff --git a/src/TensorFlowNET.Core/APIs/tf.math.cs b/src/TensorFlowNET.Core/APIs/tf.math.cs
index 8fd922d3..9df2f333 100644
--- a/src/TensorFlowNET.Core/APIs/tf.math.cs
+++ b/src/TensorFlowNET.Core/APIs/tf.math.cs
@@ -34,26 +34,7 @@ namespace Tensorflow
         /// <returns></returns>
         public static Tensor reduce_sum(Tensor input, int[] axis = null)
         {
-            Tensor rank;
-            string name;
-            using (var namescop = new ops.name_scope("", "Rank", new List<Tensor> { input }))
-            {
-                name = namescop;
-                rank = gen_array_ops.rank(input, namescop);
-            }
-
-            using (var namescope = new ops.name_scope("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 s;
+            return math_ops.reduce_sum(input);
         }
     }
 }
diff --git a/src/TensorFlowNET.Core/Gradients/gradients_impl.py.cs b/src/TensorFlowNET.Core/Gradients/gradients_impl.py.cs
index 456158e5..71801385 100644
--- a/src/TensorFlowNET.Core/Gradients/gradients_impl.py.cs
+++ b/src/TensorFlowNET.Core/Gradients/gradients_impl.py.cs
@@ -181,7 +181,11 @@ namespace Tensorflow
         {
             foreach(var x in _NonEagerInputs(op, xs))
             {
-                pending_count[x.op.Name] -= 1;
+                if (!pending_count.ContainsKey(x.op.Name))
+                    pending_count[x.op.Name] = 0;
+                else
+                    pending_count[x.op.Name] -= 1;
+
                 var ready = pending_count[x.op.Name] == 0;
 
                 if(loop_state != null && !ready)
@@ -440,22 +444,43 @@ namespace Tensorflow
                     reached_ops.Add(op);
                     foreach (var output in op.outputs)
                     {
-                        var c = _Consumers(output, func_graphs).ToList();
-                        c.ForEach(x => queue.Enqueue(x));
+                        if (_IsBackpropagatable(output))
+                        {
+                            var c = _Consumers(output, func_graphs).ToList();
+                            c.ForEach(x => queue.Enqueue(x));
+                        }
                     }
                 }
             }
         }
 
+        private static bool _IsTrainable(Tensor tensor)
+        {
+            var dtype = tensor.dtype.as_base_dtype();
+            return new TF_DataType[] {TF_DataType.TF_HALF, TF_DataType.TF_FLOAT, TF_DataType.TF_DOUBLE,
+                TF_DataType.TF_COMPLEX64, TF_DataType.TF_COMPLEX128, TF_DataType.TF_RESOURCE}.Contains(dtype);
+        }
+        private static bool _IsBackpropagatable(Tensor tensor)
+        {
+            if(_IsTrainable(tensor))
+            {
+                return true;
+            }
+            else
+            {
+                var dtype = tensor.dtype.as_base_dtype();
+                return new TF_DataType[] { TF_DataType.TF_BFLOAT16, TF_DataType.TF_VARIANT }.Contains(dtype);
+            }
+        }
+
         /// <summary>
         /// Returns the consumers of t, crossing closure boundaries where necessary.
         /// </summary>
         /// <param name="t"></param>
         /// <param name="func_graphs"></param>
-        private static List<Operation> _Consumers(Tensor t, List<object> func_graphs)
+        private static Operation[] _Consumers(Tensor t, List<object> func_graphs)
         {
-            var consumers = t.consumers();
-            return consumers;
+            return t.consumers();
         }
 
         private static List<Tensor> _AsList(object ys)
diff --git a/src/TensorFlowNET.Core/Gradients/math_grad.py.cs b/src/TensorFlowNET.Core/Gradients/math_grad.py.cs
index d6b78be6..f2b146a4 100644
--- a/src/TensorFlowNET.Core/Gradients/math_grad.py.cs
+++ b/src/TensorFlowNET.Core/Gradients/math_grad.py.cs
@@ -17,6 +17,22 @@ namespace Tensorflow
             return (grad, grad);
         }
 
+        public static (Tensor, Tensor) _SumGrad(Operation op, Tensor grad)
+        {
+            if (op.inputs[0].NDims > -1)
+            {
+
+            }
+
+            var input_shape = array_ops.shape(op.inputs[0]);
+            ops.colocate_with(input_shape);
+            var output_shape_kept_dims = math_ops.reduced_shape(input_shape, op.inputs[1]);
+            //var tile_scaling = _safe_shape_div(input_shape, output_shape_kept_dims);
+            //var grad = array_ops.reshape(grad, output_shape_kept_dims);
+
+            return (grad, grad);
+        }
+
         public static (Tensor, Tensor) _RealDivGrad(Operation op, Tensor grad)
         {
             var x = op.inputs[0];
@@ -24,9 +40,17 @@ namespace Tensorflow
 
             var sx = array_ops.shape(x);
             var sy = array_ops.shape(y);
-           // rx, ry = gen_array_ops.broadcast_gradient_args(sx, sy)
+            var (rx, ry) = gen_array_ops.broadcast_gradient_args(sx, sy);
+            x = math_ops.conj(x);
+            y = math_ops.conj(y);
 
-            return (grad, grad);
+            var realdiv1 = gen_math_ops.real_div(grad, y);
+            var reduce_sum1 = math_ops.reduce_sum(realdiv1, rx);
+            var realdiv2 = gen_math_ops.real_div(-x, y);
+            var realdiv3 = gen_math_ops.real_div(realdiv2, y);
+            var reduce_sum2 = math_ops.reduce_sum(grad * realdiv3, ry);
+
+            return (gen_array_ops.reshape(reduce_sum1, sx), gen_array_ops.reshape(reduce_sum2, sy));
         }
     }
 }
diff --git a/src/TensorFlowNET.Core/Operations/array_ops.py.cs b/src/TensorFlowNET.Core/Operations/array_ops.py.cs
index 6da5ad2a..2753853e 100644
--- a/src/TensorFlowNET.Core/Operations/array_ops.py.cs
+++ b/src/TensorFlowNET.Core/Operations/array_ops.py.cs
@@ -53,6 +53,11 @@ namespace Tensorflow
             }
         }
 
+        public static Tensor rank(Tensor input, string name = "")
+        {
+            return math_ops.rank_internal(input, name, optimize: true);
+        }
+
         /// <summary>
         /// Returns the shape of a tensor.
         /// </summary>
@@ -68,11 +73,14 @@ namespace Tensorflow
             return shape_internal(input, name, optimize: true, out_type: out_type);
         }
 
-        private static Tensor shape_internal(Tensor input, string name = "", bool optimize = true, TF_DataType out_type = TF_DataType.TF_INT32)
+        public static Tensor size(Tensor input, string name = "", TF_DataType out_type = TF_DataType.TF_INT32)
         {
-            Tensor result = null;
+            return size_internal(input, name, optimize: true, out_type: out_type);
+        }
 
-            Python.with<ops.name_scope>(new ops.name_scope(name, "Shape", new Tensor[] { input }), scope =>
+        private static Tensor shape_internal(Tensor input, string name = "", bool optimize = true, TF_DataType out_type = TF_DataType.TF_INT32)
+        {
+            return Python.with<ops.name_scope, Tensor>(new ops.name_scope(name, "Shape", new Tensor[] { input }), scope =>
             {
                 name = scope;
 
@@ -83,16 +91,46 @@ namespace Tensorflow
                     if (optimize && input_shape.is_fully_defined())
                     {
                         var nd = np.array(input_tensor.shape, out_type.as_numpy_datatype());
-                        result = constant_op.constant(nd, name);
+                        return constant_op.constant(nd, name);
                     }
                 }
                 else
                 {
                     // result = gen_array_ops.shape();
                 }
+
+                return null;
             });
+        }
 
-            return result;
+        private static Tensor size_internal(Tensor input, string name = "", bool optimize = true, TF_DataType out_type = TF_DataType.TF_INT32)
+        {
+            return Python.with<ops.name_scope, Tensor>(new ops.name_scope(name, "Size", new Tensor[] { input }), scope =>
+            {
+                name = scope;
+
+                if (!tf.context.executing_eagerly())
+                {
+                    var input_tensor = ops.convert_to_tensor(input);
+                    var input_shape = tensor_util.to_shape(input_tensor.shape);
+                    if (optimize)
+                    {
+                        if (input_shape.is_fully_defined())
+                        {
+                            var nd = np.array(input_tensor.shape, out_type.as_numpy_datatype());
+                            return constant_op.constant(nd, name);
+                        }
+                    }
+
+                    return gen_array_ops.size(input, name: name, out_type: out_type);
+                }
+                else
+                {
+                    // result = gen_array_ops.shape();
+                }
+
+                return null;
+            });
         }
     }
 }
diff --git a/src/TensorFlowNET.Core/Operations/gen_array_ops.cs b/src/TensorFlowNET.Core/Operations/gen_array_ops.cs
index 9acc7fe8..77e9136f 100644
--- a/src/TensorFlowNET.Core/Operations/gen_array_ops.cs
+++ b/src/TensorFlowNET.Core/Operations/gen_array_ops.cs
@@ -60,9 +60,30 @@ namespace Tensorflow
             return _op.outputs[0];
         }
 
+        /// <summary>
+        /// Return the reduction indices for computing gradients of s0 op s1 with broadcast.
+        /// </summary>
+        /// <param name="s0">A `Tensor`. Must be one of the following types: `int32`, `int64`.</param>
+        /// <param name="s1">A `Tensor`. Must have the same type as `s0`.</param>
+        /// <param name="name">A name for the operation (optional).</param>
+        /// <returns>A tuple of `Tensor` objects (r0, r1).</returns>
         public static (Tensor, Tensor) broadcast_gradient_args(Tensor s0, Tensor s1, string name = "")
         {
-            return (null, null);
+            var _op = _op_def_lib._apply_op_helper("BroadcastGradientArgs", name, new { s0, s1 });
+
+            return (_op.outputs[0], _op.outputs[1]);
+        }
+
+        public static Tensor reshape(Tensor tensor, Tensor shape, string name = "")
+        {
+            var _op = _op_def_lib._apply_op_helper("Reshape", name, new { tensor, shape });
+            return _op.outputs[0];
+        }
+
+        public static Tensor size(Tensor input, TF_DataType out_type = TF_DataType.TF_INT32, string name = "")
+        {
+            var _op = _op_def_lib._apply_op_helper("Size", name, new { input, out_type });
+            return _op.outputs[0];
         }
     }
 }
diff --git a/src/TensorFlowNET.Core/Operations/gen_math_ops.cs b/src/TensorFlowNET.Core/Operations/gen_math_ops.cs
index 2e38b798..140e8e29 100644
--- a/src/TensorFlowNET.Core/Operations/gen_math_ops.cs
+++ b/src/TensorFlowNET.Core/Operations/gen_math_ops.cs
@@ -17,9 +17,16 @@ namespace Tensorflow
             return _op.outputs[0];
         }
 
-        public static Tensor sub(Tensor x, Tensor y)
+        public static Tensor neg(Tensor x, string name = "")
         {
-            var _op = _op_def_lib._apply_op_helper("Sub", name: "sub", args: new { x, y });
+            var _op = _op_def_lib._apply_op_helper("Neg", name, args: new { x });
+
+            return _op.outputs[0];
+        }
+
+        public static Tensor sub(Tensor x, Tensor y, string name = "")
+        {
+            var _op = _op_def_lib._apply_op_helper("Sub", name, args: new { x, y });
 
             return _op.outputs[0];
         }
@@ -31,9 +38,9 @@ namespace Tensorflow
             return _op.outputs[0];
         }
 
-        public static Tensor real_div(Tensor x, Tensor y)
+        public static Tensor real_div(Tensor x, Tensor y, string name = "")
         {
-            var _op = _op_def_lib._apply_op_helper("RealDiv", name: "truediv", args: new { x, y });
+            var _op = _op_def_lib._apply_op_helper("RealDiv", name, args: new { x, y });
 
             return _op.outputs[0];
         }
@@ -61,9 +68,9 @@ namespace Tensorflow
             return _op.outputs[0];
         }
 
-        public static Tensor sum(Tensor input, Tensor axis = null)
+        public static Tensor sum(Tensor input, Tensor axis = null, bool keep_dims = false, string name = "")
         {
-            var _op = _op_def_lib._apply_op_helper("Sum", args: new { input, reduction_indices = axis, keep_dims = false });
+            var _op = _op_def_lib._apply_op_helper("Sum", name, args: new { input, reduction_indices = axis, keep_dims });
 
             return _op.outputs[0];
         }
diff --git a/src/TensorFlowNET.Core/Operations/math_ops.py.cs b/src/TensorFlowNET.Core/Operations/math_ops.py.cs
index 078de45c..05893d54 100644
--- a/src/TensorFlowNET.Core/Operations/math_ops.py.cs
+++ b/src/TensorFlowNET.Core/Operations/math_ops.py.cs
@@ -6,6 +6,104 @@ namespace Tensorflow
 {
     public class math_ops
     {
+        /// <summary>
+        /// Helper function for reduction ops.
+        /// </summary>
+        /// <param name="input_shape">1-D Tensor, the shape of the Tensor being reduced.</param>
+        /// <param name="axes">1-D Tensor, the reduction axes.</param>
+        /// <returns>A 1-D Tensor, the output shape as if keepdims were set to True.</returns>
+        public static Tensor reduced_shape(Tensor input_shape, Tensor axes)
+        {
+            input_shape = to_int32(input_shape);
+            axes = to_int32(axes);
+
+            var input_rank = array_ops.size(input_shape);
+            axes = (axes + input_rank) % input_rank;
+
+            return null;
+        }
+
+        /// <summary>
+        /// Casts a tensor to type `int32`.
+        /// </summary>
+        /// <param name="x">A `Tensor` or `SparseTensor` or `IndexedSlices`.</param>
+        /// <param name="name">A name for the operation (optional).</param>
+        /// <returns>A `Tensor` or `SparseTensor` or `IndexedSlices` with same shape as `x` with type `int32`.</returns>
+        private static Tensor to_int32(Tensor x, string name = "ToInt32")
+        {
+            return __case__(x, TF_DataType.TF_INT32, name: name);
+        }
+
+        /// <summary>
+        /// Casts a tensor to a new type.
+        /// </summary>
+        /// <param name="x"></param>
+        /// <param name="dtype"></param>
+        /// <param name="name"></param>
+        /// <returns>A `Tensor` or `SparseTensor` or `IndexedSlices` with same shape as `x` and same type as `dtype`.</returns>
+        public static Tensor __case__(Tensor x, TF_DataType dtype, string name = "")
+        {
+            var base_type = dtype.as_base_dtype();
+            if (x is Tensor && base_type == x.dtype)
+                return x;
+
+            // math_ops.py cast
+            throw new NotImplementedException();
+        }
+
+        public static Tensor reduce_sum(Tensor input_tensor, Tensor axis = null, bool keepdims = false)
+        {
+            var r = _ReductionDims(input_tensor, axis);
+            var m = gen_math_ops.sum(input_tensor, r);
+            return _may_reduce_to_scalar(keepdims, m);
+        }
+
+        private static Tensor _may_reduce_to_scalar(bool keepdims, Tensor output)
+        {
+            output.shape = new long[0];
+            return output;
+        }
+
+        private static Tensor _ReductionDims(Tensor x, Tensor axis)
+        {
+            if (axis != null)
+            {
+                return axis;
+            }
+            else
+            {
+                var rank = array_ops.rank(x);
+                return range(0, rank, 1);
+            }
+        }
+
+        public static Tensor range(object start, Tensor limit = null, object delta = null, TF_DataType dtype = TF_DataType.DtInvalid, string name = "range" )
+        {
+            return Python.with<ops.name_scope, Tensor>(new ops.name_scope(name, "Range", new object[] { start, limit, delta }), scope =>
+            {
+                name = scope;
+                var start1 = ops.convert_to_tensor(start, name: "start");
+                var limit1 = ops.convert_to_tensor(limit, name: "limit");
+                var delta1 = ops.convert_to_tensor(delta, name: "delta");
+
+                return gen_math_ops.range(start1, limit1, delta1, name);
+            });
+        }
+
+        public static Tensor rank_internal(Tensor input, string name = "", bool optimize = true)
+        {
+            return Python.with<ops.name_scope, Tensor>(new ops.name_scope(name, "Rank", new List<Tensor> { input }), scope =>
+            {
+                name = scope;
+                var input_tensor = ops.convert_to_tensor(input);
+                var input_shape = tensor_util.to_shape(input_tensor.shape);
+                if (optimize && input_shape.NDim == null)
+                    return constant_op.constant(input_shape.NDim);
+                else
+                    return gen_array_ops.rank(input, name);
+            });
+        }
+
         public static Tensor matmul(Tensor a, Tensor b,
             bool transpose_a = false, bool transpose_b = false,
             bool adjoint_a = false, bool adjoint_b = false,
@@ -31,5 +129,24 @@ namespace Tensorflow
 
             return result;
         }
+
+        /// <summary>
+        /// Returns the complex conjugate of a complex number.
+        /// </summary>
+        /// <param name="x">`Tensor` to conjugate.  Must have numeric or variant type.</param>
+        /// <param name="name">A name for the operation (optional).</param>
+        /// <returns>A `Tensor` that is the conjugate of `x` (with the same type).</returns>
+        public static Tensor conj(Tensor x, string name = "")
+        {
+            var dt = x.dtype;
+            if (dt.is_floating() || dt.is_integer())
+                return x;
+
+            return Python.with<ops.name_scope, Tensor>(new ops.name_scope(name, "Conj", new List<Tensor> { x }), scope =>
+            {
+
+                return x;
+            });
+        }
     }
 }
diff --git a/src/TensorFlowNET.Core/Tensors/Tensor.Implicit.cs b/src/TensorFlowNET.Core/Tensors/Tensor.Implicit.cs
index ada0c89a..aed5d4a1 100644
--- a/src/TensorFlowNET.Core/Tensors/Tensor.Implicit.cs
+++ b/src/TensorFlowNET.Core/Tensors/Tensor.Implicit.cs
@@ -6,15 +6,19 @@ namespace Tensorflow
 {
     public partial class Tensor
     {
-        public static implicit operator Tensor(double scalar)
+        /// <summary>
+        /// Issue unresolved, will cause name_scope problem.
+        /// </summary>
+        /// <param name="scalar"></param>
+        /*public static implicit operator Tensor(double scalar)
         {
             return constant_op.constant(scalar);
-        }
+        }*/
 
-        public static implicit operator Tensor(int scalar)
+        /*public static implicit operator Tensor(int scalar)
         {
             return constant_op.constant(scalar);
-        }
+        }*/
 
         public static implicit operator int(Tensor tensor)
         {
diff --git a/src/TensorFlowNET.Core/Tensors/Tensor.Operators.cs b/src/TensorFlowNET.Core/Tensors/Tensor.Operators.cs
index 9923bb48..2cf600f7 100644
--- a/src/TensorFlowNET.Core/Tensors/Tensor.Operators.cs
+++ b/src/TensorFlowNET.Core/Tensors/Tensor.Operators.cs
@@ -8,14 +8,24 @@ namespace Tensorflow
     {
         public static Tensor operator +(Tensor x, Tensor y)
         {
-            Tensor t = null;
+            return Python.with<ops.name_scope, Tensor>(new ops.name_scope("", "add", new Tensor[] { x, y }), scope =>
+            {
+                return gen_math_ops.add(x, y, scope);
+            });
+        }
 
-            Python.with<ops.name_scope>(new ops.name_scope("", "add", new Tensor[] { x, y }), scope =>
+        public static Tensor operator +(Tensor x, int y)
+        {
+            return Python.with<ops.name_scope, Tensor>(new ops.name_scope("", "add", new object[] { x, y }), scope =>
             {
-                t = gen_math_ops.add(x, y, scope);
+                var y1 = ops.convert_to_tensor(y, x.dtype.as_base_dtype(), name: "y");
+                return gen_math_ops.add(x, y1, scope);
             });
+        }
 
-            return t;
+        public static Tensor operator -(Tensor t1)
+        {
+            return gen_math_ops.neg(t1);
         }
 
         public static Tensor operator -(Tensor t1, Tensor t2)
@@ -35,19 +45,41 @@ namespace Tensorflow
 
         public static Tensor operator *(Tensor x, Tensor y)
         {
-            Tensor t = null;
+            return Python.with<ops.name_scope, Tensor>(new ops.name_scope("", "mul", new Tensor[] { x, y }), scope =>
+            {
+                return gen_math_ops.mul(x, y, name: scope);
+            });
+        }
 
-            Python.with<ops.name_scope>(new ops.name_scope("", "mul", new Tensor[] { x, y }), scope =>
+        public static Tensor operator *(Tensor x, int y)
+        {
+            return Python.with<ops.name_scope, Tensor>(new ops.name_scope("", "mul", new object[] { x, y }), scope =>
             {
-                t = gen_math_ops.mul(x, y, name: scope);
+                var y1 = ops.convert_to_tensor(y, x.dtype.as_base_dtype(), name: "y");
+                return gen_math_ops.mul(x, y1, name: scope);
             });
+        }
 
-            return t;
+        public static Tensor operator /(Tensor x, Tensor y)
+        {
+            return Python.with<ops.name_scope, Tensor>(new ops.name_scope("truediv/", "truediv", new Tensor[] { x, y }), scope =>
+            {
+                return gen_math_ops.real_div(x, y, scope);
+            });
+        }
+
+        public static Tensor operator /(Tensor x, double y)
+        {
+            return Python.with<ops.name_scope, Tensor>(new ops.name_scope("truediv/", "truediv", new object[] { x, y }), scope =>
+            {
+                var y1 = ops.convert_to_tensor(y, dtype: x.dtype.as_base_dtype(), name: "y");
+                return gen_math_ops.real_div(x, y1, scope);
+            });
         }
 
-        public static Tensor operator /(Tensor t1, Tensor t2)
+        public static Tensor operator %(Tensor x, Tensor y)
         {
-            return gen_math_ops.real_div(t1, t2);
+            throw new NotImplementedException("math mod is not implemented");
         }
     }
 }
diff --git a/src/TensorFlowNET.Core/Tensors/Tensor.cs b/src/TensorFlowNET.Core/Tensors/Tensor.cs
index 65f3742d..90b7c2dc 100644
--- a/src/TensorFlowNET.Core/Tensors/Tensor.cs
+++ b/src/TensorFlowNET.Core/Tensors/Tensor.cs
@@ -38,6 +38,7 @@ namespace Tensorflow
         public ulong size => _handle == IntPtr.Zero ? 0 : bytesize / dataTypeSize;
         public IntPtr buffer => _handle == IntPtr.Zero ? IntPtr.Zero : c_api.TF_TensorData(_handle);
         public int num_consumers(TF_Output oper_out) => _handle == IntPtr.Zero ? 0 : c_api.TF_OperationOutputNumConsumers(oper_out);
+
         public long[] shape
         {
             get
@@ -60,7 +61,10 @@ namespace Tensorflow
 
             set
             {
-                // c_api.TF_GraphSetTensorShape_wrapper
+                if (value == null)
+                    c_api.TF_GraphSetTensorShape(this.Graph, this._as_tf_output(), null, -1, status);
+                else
+                    c_api.TF_GraphSetTensorShape(this.Graph, this._as_tf_output(), value, value.Length, status);
             }
         }
         
@@ -170,11 +174,12 @@ namespace Tensorflow
             _id = ops.uid();
         }
 
-        public List<Operation> consumers()
+        public Operation[] Consumers => consumers();
+        public Operation[] consumers()
         {
             var output = _as_tf_output();
             var consumer_names = c_api.TF_OperationOutputConsumers_wrapper(output);
-            return consumer_names.Select(x => Graph.OperationByName(x)).ToList();
+            return consumer_names.Select(x => Graph.OperationByName(x)).ToArray();
         }
 
         public TF_Output _as_tf_output()
diff --git a/src/TensorFlowNET.Core/Tensors/TensorShape.cs b/src/TensorFlowNET.Core/Tensors/TensorShape.cs
index 15ff64eb..e63543d6 100644
--- a/src/TensorFlowNET.Core/Tensors/TensorShape.cs
+++ b/src/TensorFlowNET.Core/Tensors/TensorShape.cs
@@ -23,7 +23,7 @@ namespace Tensorflow
         /// <returns></returns>
         public bool is_fully_defined()
         {
-            return Dimensions != null; 
+            return Dimensions != null && Dimensions.Count(x => x > 0) > 0;
         }
     }
 }
diff --git a/src/TensorFlowNET.Core/Tensors/dtypes.cs b/src/TensorFlowNET.Core/Tensors/dtypes.cs
index 396fdd87..286ea603 100644
--- a/src/TensorFlowNET.Core/Tensors/dtypes.cs
+++ b/src/TensorFlowNET.Core/Tensors/dtypes.cs
@@ -82,5 +82,15 @@ namespace Tensorflow
         {
             return type == TF_DataType.TF_COMPLEX || type == TF_DataType.TF_COMPLEX64 || type == TF_DataType.TF_COMPLEX128;
         }
+
+        public static bool is_integer(this TF_DataType type)
+        {
+            return type == TF_DataType.TF_INT8 || type == TF_DataType.TF_INT16 || type == TF_DataType.TF_INT32 || type == TF_DataType.TF_INT64;
+        }
+
+        public static bool is_floating(this TF_DataType type)
+        {
+            return type == TF_DataType.TF_HALF || type == TF_DataType.TF_FLOAT || type == TF_DataType.TF_DOUBLE;
+        }
     }
 }
diff --git a/src/TensorFlowNET.Core/ops.py.cs b/src/TensorFlowNET.Core/ops.py.cs
index 84c7deff..823fc6fd 100644
--- a/src/TensorFlowNET.Core/ops.py.cs
+++ b/src/TensorFlowNET.Core/ops.py.cs
@@ -220,6 +220,11 @@ namespace Tensorflow
             _colocate_with_for_gradient(op, null, ignore_existing);
         }
 
+        public static void colocate_with(Tensor tensor, bool ignore_existing = false)
+        {
+            _colocate_with_for_gradient(tensor.op, null, ignore_existing);
+        }
+
         private static void _colocate_with_for_gradient(Operation op, int? gradient_uid, bool ignore_existing = false)
         {
             var default_graph = get_default_graph();
@@ -290,10 +295,12 @@ namespace Tensorflow
                 {
                     case "Add":
                         return math_grad._AddGrad(op, out_grads);
+                    case "Sum":
+                        return math_grad._SumGrad(op, out_grads);
                     case "RealDiv":
                         return math_grad._RealDivGrad(op, out_grads);
                     default:
-                        throw new NotImplementedException("get_gradient_function");
+                        throw new NotImplementedException($"get_gradient_function {oper.type}");
                 }
                 /*var result = typeof(math_grad).GetMethod($"_{op.type}Grad").Invoke(null, new object[] { op, out_grads });
                 var p1 = result.GetType().GetProperty("Item1");
diff --git a/test/TensorFlowNET.Examples/TensorFlowNET.Examples.csproj b/test/TensorFlowNET.Examples/TensorFlowNET.Examples.csproj
index b7436a2e..982acadb 100644
--- a/test/TensorFlowNET.Examples/TensorFlowNET.Examples.csproj
+++ b/test/TensorFlowNET.Examples/TensorFlowNET.Examples.csproj
@@ -14,4 +14,8 @@
     <ProjectReference Include="..\..\src\TensorFlowNET.Core\TensorFlowNET.Core.csproj" />
   </ItemGroup>
 
+  <ItemGroup>
+    <Folder Include="python\" />
+  </ItemGroup>
+
 </Project>
diff --git a/test/TensorFlowNET.Examples/python/linear_regression.py b/test/TensorFlowNET.Examples/python/linear_regression.py
new file mode 100644
index 00000000..eb9bfc87
--- /dev/null
+++ b/test/TensorFlowNET.Examples/python/linear_regression.py
@@ -0,0 +1,94 @@
+'''
+A linear regression learning algorithm example using TensorFlow library.
+Author: Aymeric Damien
+Project: https://github.com/aymericdamien/TensorFlow-Examples/
+'''
+
+from __future__ import print_function
+
+import tensorflow as tf
+import numpy
+import matplotlib.pyplot as plt
+rng = numpy.random
+
+# Parameters
+learning_rate = 0.01
+training_epochs = 1000
+display_step = 50
+
+# Training Data
+train_X = numpy.asarray([3.3,4.4,5.5,6.71,6.93,4.168,9.779,6.182,7.59,2.167,
+                         7.042,10.791,5.313,7.997,5.654,9.27,3.1])
+train_Y = numpy.asarray([1.7,2.76,2.09,3.19,1.694,1.573,3.366,2.596,2.53,1.221,
+                         2.827,3.465,1.65,2.904,2.42,2.94,1.3])
+n_samples = train_X.shape[0]
+
+# tf Graph Input
+X = tf.placeholder("float")
+Y = tf.placeholder("float")
+
+# Set model weights
+W = tf.Variable(rng.randn(), name="weight")
+b = tf.Variable(rng.randn(), name="bias")
+
+# Construct a linear model
+mul = tf.multiply(X, W)
+pred = tf.add(mul, b)
+
+# Mean squared error
+sub = pred-Y
+pow = tf.pow(sub, 2)
+
+reduce = tf.reduce_sum(pow)
+cost = reduce/(2*n_samples)
+# Gradient descent
+#  Note, minimize() knows to modify W and b because Variable objects are trainable=True by default
+grad = tf.train.GradientDescentOptimizer(learning_rate)
+optimizer = grad.minimize(cost)
+
+# Initialize the variables (i.e. assign their default value)
+init = tf.global_variables_initializer()
+
+# Start training
+with tf.Session() as sess:
+
+    # Run the initializer
+    sess.run(init)
+
+    # Fit all training data
+    for epoch in range(training_epochs):
+        for (x, y) in zip(train_X, train_Y):
+            sess.run(optimizer, feed_dict={X: x, Y: y})
+
+        # Display logs per epoch step
+        if (epoch+1) % display_step == 0:
+            c = sess.run(cost, feed_dict={X: train_X, Y:train_Y})
+            print("Epoch:", '%04d' % (epoch+1), "cost=", "{:.9f}".format(c), \
+                "W=", sess.run(W), "b=", sess.run(b))
+
+    print("Optimization Finished!")
+    training_cost = sess.run(cost, feed_dict={X: train_X, Y: train_Y})
+    print("Training cost=", training_cost, "W=", sess.run(W), "b=", sess.run(b), '\n')
+
+    # Graphic display
+    plt.plot(train_X, train_Y, 'ro', label='Original data')
+    plt.plot(train_X, sess.run(W) * train_X + sess.run(b), label='Fitted line')
+    plt.legend()
+    plt.show()
+
+    # Testing example, as requested (Issue #2)
+    test_X = numpy.asarray([6.83, 4.668, 8.9, 7.91, 5.7, 8.7, 3.1, 2.1])
+    test_Y = numpy.asarray([1.84, 2.273, 3.2, 2.831, 2.92, 3.24, 1.35, 1.03])
+
+    print("Testing... (Mean square loss Comparison)")
+    testing_cost = sess.run(
+        tf.reduce_sum(tf.pow(pred - Y, 2)) / (2 * test_X.shape[0]),
+        feed_dict={X: test_X, Y: test_Y})  # same function as cost above
+    print("Testing cost=", testing_cost)
+    print("Absolute mean square loss difference:", abs(
+        training_cost - testing_cost))
+
+    plt.plot(test_X, test_Y, 'bo', label='Testing data')
+    plt.plot(train_X, sess.run(W) * train_X + sess.run(b), label='Fitted line')
+    plt.legend()
+    plt.show()
\ No newline at end of file