gradients_impl. not finish yet.

src/TensorFlowNET.Core/Gradients/AggregationMethod.cs

@@ -0,0 +1,15 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace Tensorflow
+{
+    public class AggregationMethod
+    {
+        public static int ADD_N = 0;
+        public static int DEFAULT = ADD_N;
+        // The following are experimental and may not be supported in future releases.
+        public static int EXPERIMENTAL_TREE = 1;
+        public static int EXPERIMENTAL_ACCUMULATE_N = 2;
+    }
+}

src/TensorFlowNET.Core/Gradients/gradients_impl.py.cs

@@ -0,0 +1,32 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace Tensorflow
+{
+    public class gradients_impl
+    {
+        public static void gradients(object ys,
+            object xs, 
+            List<Tensor> grad_ys = null,
+            string name = "gradients",
+            bool colocate_gradients_with_ops = false,
+            bool gate_gradients = false,
+            int? aggregation_method = null)
+        {
+            _GradientsHelper(ys, xs, grad_ys, name, colocate_gradients_with_ops, gate_gradients);
+        }
+
+        public static void _GradientsHelper(object ys,
+            object xs,
+            List<Tensor> grad_ys = null,
+            string name = "gradients",
+            bool colocate_gradients_with_ops = false,
+            bool gate_gradients = false,
+            Graph src_graph = null)
+        {
+            if (src_graph == null)
+                src_graph = ops.get_default_graph();
+        }
+    }
+}

src/TensorFlowNET.Core/Tensors/Tensor.cs

@@ -222,7 +222,7 @@ namespace Tensorflow
                 }
             }
 
-            return "";
+            return $"{name} {dtype} {rank} {string.Join(",", shape)}";
         }
 
         public void Dispose()

src/TensorFlowNET.Core/Train/Optimizer.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Linq;
 using System.Text;
 using distribute_lib = Tensorflow.Distribute;
 
@@ -48,8 +49,10 @@ namespace Tensorflow
         /// <param name="gate_gradients"></param>
         public List<KeyValuePair<object, object>> compute_gradients(Tensor loss,
             List<RefVariable> var_list = null,
+            int? aggregation_method = null,
             GateGradientType gate_gradients = GateGradientType.GATE_OP,
-            bool colocate_gradients_with_ops = false)
+            bool colocate_gradients_with_ops = false,
+            List<Tensor> grad_loss = null)
         {
             int num_towers = 1;
             if(distribute_lib.get_loss_reduction() == VariableAggregationType.MEAN)
@@ -65,10 +68,13 @@ namespace Tensorflow
                     break;
             }
 
-            foreach(var v in var_list)
-            {
+            var processors = var_list.Select(v => optimizer._get_processor(v));
+            var var_refs = processors.Select(x => x.target()).ToList();
 
-            }
+            gradients_impl.gradients(loss, var_refs, grad_ys: grad_loss,
+                gate_gradients: (gate_gradients == GateGradientType.GATE_OP),
+                aggregation_method: aggregation_method,
+                colocate_gradients_with_ops: colocate_gradients_with_ops);
 
             return null;
         }

src/TensorFlowNET.Core/Train/_OptimizableVariable.cs

@@ -0,0 +1,12 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace Tensorflow
+{
+    public interface _OptimizableVariable
+    {
+        Tensor target();
+        void update_op(Graph g);
+    }
+}

src/TensorFlowNET.Core/Train/optimizer.py.cs

@@ -0,0 +1,34 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace Tensorflow
+{
+    public class optimizer
+    {
+        public static _OptimizableVariable _get_processor(RefVariable v)
+        {
+            return new _RefVariableProcessor(v);
+        }
+    }
+
+    public class _RefVariableProcessor : _OptimizableVariable
+    {
+        private RefVariable _v;
+
+        public _RefVariableProcessor(RefVariable v)
+        {
+            _v = v;
+        }
+
+        public Tensor target()
+        {
+            return _v._ref();
+        }
+
+        public void update_op(Graph g)
+        {
+            
+        }
+    }
+}

src/TensorFlowNET.Core/Variables/RefVariable.cs

@@ -78,6 +78,11 @@ namespace Tensorflow
             ops.add_to_collections(collections, this);
         }
 
+        public Tensor _ref()
+        {
+            return _variable;
+        }
+
         public static implicit operator _VariableScopeStore(RefVariable variable)
         {
             return null;