Fix gradient of squared_difference #787

src/TensorFlowNET.Core/Gradients/nn_grad.cs

@@ -122,13 +122,14 @@ namespace Tensorflow.Gradients
         [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];
+            var scale = ops.convert_to_tensor(2.0f, dtype: x.dtype);
+            var x_grad = math_ops.scalar_mul(scale, grads[0]) * (x - y);
             return new Tensor[]
             {
-                x,
-                y
+                x_grad,
+                -x_grad
             };
         }
         /// <summary>

src/TensorFlowNET.Core/Operations/math_ops.cs

@@ -272,6 +272,9 @@ namespace Tensorflow
         public static Tensor mul_no_nan<Tx, Ty>(Tx x, Ty y, string name = null)
             => gen_math_ops.mul_no_nan(x, y, name: name);
 
+        public static Tensor scalar_mul<Tscale, Tx>(Tscale scale, Tx x, string name = null)
+            => tf.Context.ExecuteOp("Mul", name, new ExecuteOpArgs(scale, x));
+
         public static Tensor real(Tensor input, string name = null)
         {
             return tf_with(ops.name_scope(name, "Real", new[] { input }), scope =>

src/TensorFlowNET.Core/tensorflow.cs

@@ -48,7 +48,7 @@ namespace Tensorflow
         public tensorflow()
         {
             Logger = new LoggerConfiguration()
-                .MinimumLevel.Error()
+                .MinimumLevel.Debug()
                 .WriteTo.Console()
                 .CreateLogger();
 

test/TensorFlowNET.UnitTest/GradientTest/GradientEagerTest.cs

@@ -25,7 +25,6 @@ namespace TensorFlowNET.UnitTest.Gradient
             Assert.AreEqual((float)grad, 3.0f);
         }
 
-        [Ignore]
         [TestMethod]
         public void SquaredDifference_Constant()
         {