Pack/Unpack gradient. #847

Author: Oceania2018

src/TensorFlowNET.Core/Gradients/array_grad.cs

@@ -223,6 +223,22 @@ public static Tensor[] _ReshapeGrad(Operation op, Tensor[] grads)
             return new Tensor[] { array_ops.reshape(grads[0], array_ops.shape(op.inputs[0])), null };
         }
 
+        [RegisterGradient("Pack")]
+        public static Tensor[] _PackGrad(Operation op, Tensor[] grads)
+        {
+            var grad = grads[0];
+            var num = op.get_attr<int>("N");
+            var axis = op.get_attr<int>("axis");
+            return array_ops.unstack(grad, num: num, axis: axis);
+        }
+
+        [RegisterGradient("Unpack")]
+        public static Tensor[] _UnpackGrad(Operation op, Tensor[] grads)
+        {
+            var axis = op.get_attr<int>("axis");
+            return new[] { array_ops.stack(grads, axis: axis) };
+        }
+
         [RegisterGradient("Pad")]
         public static Tensor[] _PadGrad(Operation op, Tensor[] grads)
         {

src/TensorFlowNET.Core/Operations/array_ops.cs

@@ -494,20 +494,12 @@ public static Tensor stack(Tensor[] values, int axis = 0, string name = "stack")
                 return ops.convert_to_tensor(values, name: name);
             }
 
-            var value_shape = ops.convert_to_tensor(values[0], name: name).shape;
-
             return gen_array_ops.pack(values, axis: axis, name: name);
         }
 
         public static Tensor[] unstack(Tensor value, int? num = null, int axis = 0, string name = "unstack")
         {
-            if (num == null)
-            {
-                value = ops.convert_to_tensor(value);
-                var value_shape = value.shape;
-                num = (int)value_shape.dims[axis];
-            }
-
+            num = num ?? value.shape.as_int_list()[axis];
             return gen_array_ops.unpack(value, num: num.Value, axis: axis, name: name);
         }
 

src/TensorFlowNET.Core/Operations/gen_array_ops.cs

@@ -265,10 +265,8 @@ public static (Tensor, Tensor) unique(Tensor x, TF_DataType out_idx = TF_DataTyp
         }
 
         public static Tensor[] unpack(Tensor value, int num, int axis = 0, string name = null)
-        {
-            var _op = tf.OpDefLib._apply_op_helper("Unpack", name, new { value, num, axis });
-            return _op.outputs;
-        }
+            => tf.Context.ExecuteOp("Unpack", name, new ExecuteOpArgs(value, num)
+                    .SetAttributes(new { axis }));
 
         public static Tensor where(Tensor condition, string name = null)
         {