Gradient support (#159)

These changes and the fix in native API resolves issue #25
Now, add gradients works correctly

The test will fail until a new version of TensorFlowSharp with updated native libraries is released.

Author: Dorokhov

TensorFlowSharp/Tensorflow.cs

@@ -1003,10 +1003,10 @@ public TFOutput [] AddGradients (TFOutput [] y, TFOutput [] x, TFOutput [] dx =
 					fixed (TFOutput* py = &y [0]) {
 						fixed (TFOutput* px = &x [0]) {
 							if (dx == null) {
-								TF_AddGradients (handle, py, y.Length, px, x.Length, (TFOutput*)null, status.Handle, pret);
+								TF_AddGradients (handle, py, y.Length, px, x.Length, (TFOutput*)null, cstatus.Handle, pret);
 							} else {
 								fixed (TFOutput* pdx = &dx [0]) {
-									TF_AddGradients (handle, py, y.Length, px, x.Length, pdx, status.Handle, pret);
+									TF_AddGradients (handle, py, y.Length, px, x.Length, pdx, cstatus.Handle, pret);
 								}
 							}
 						}

tests/TensorFlowSharp.Tests.CSharp/GradientTests.cs

@@ -0,0 +1,27 @@
+using TensorFlow;
+using Xunit;
+
+namespace TensorFlowSharp.Tests.CSharp
+{
+	public class GradientTests
+	{
+		[Fact]
+		public void ShouldAddGradients ()
+		{
+			using (var graph = new TFGraph ())
+			using (var session = new TFSession (graph)) {
+				var x = graph.Const (3.0);
+
+				var y1 = graph.Square (x, "Square1");
+				var y2 = graph.Square (y1, "Square2");
+
+				var y3 = graph.Square (y2, "Square3");
+				var g = graph.AddGradients (new TFOutput [] { y1, y3 }, new [] { x });
+
+				var r = session.Run (new TFOutput [] { }, new TFTensor [] { }, g);
+				var dy = (double)r [0].GetValue ();
+				Assert.Equal (17502.0, dy);
+			}
+		}
+	}
+}

tests/TensorFlowSharp.Tests.CSharp/TensorFlowSharp.Tests.CSharp.csproj

@@ -63,6 +63,7 @@
     </Reference>
   </ItemGroup>
   <ItemGroup>
+    <Compile Include="GradientTests.cs" />
     <Compile Include="ArrayTests.cs" />
     <Compile Include="TensorTests.cs" />
     <Compile Include="ClipTests.cs" />