Merge branch 'master' of https://github.com/SciSharp/TensorFlow.NET

Author: Oceania2018

src/TensorFlowNET.Core/Gradients/nn_grad.cs

@@ -111,14 +111,26 @@ public static Tensor[] _SparseSoftmaxCrossEntropyWithLogitsGrad(Operation op, Te
               "implementation's interaction with tf.gradients()");
 
             var grad_0 = grads[0];
-
+            
             return new Tensor[]
             {
                 _BroadcastMul(grad_0, sparse_softmax_grad_without_gradient),
                 null
             };
         }
 
+        [RegisterGradient("SquaredDifference")]
+        public static Tensor[] _SquaredDifferenceGrad(Operation op, Tensor[] grads)
+        {
+           //"""Returns the gradient for (x-y)^2."""
+            Tensor x = op.inputs[0];
+            Tensor y = op.inputs[1];
+            return new Tensor[]
+            {
+                x,
+                y
+            };
+        }
         /// <summary>
         /// Gradient function for Conv2D.
         /// </summary>