Add gradient for sigmoid (#245)

tensorflow-ops/src/TensorFlow/Gradient.hs

@@ -85,6 +85,8 @@ import TensorFlow.Ops
     , shape
     , softmaxCrossEntropyWithLogits
     , sum
+    , sigmoid
+    , sigmoidGrad
     , scalarize
     , vector
     , zerosLike
@@ -481,6 +483,7 @@ opGrad "Neg" _ [_] [dz] = [Just $ negate $ expr dz]
 opGrad "Relu" _ [toT -> x] [dz] = [Just $ reluGrad dz x]
 opGrad "ReluGrad" _ [_, toT -> x ] [dz] = [Just $ reluGrad dz x, Just $ CoreOps.zerosLike x]
 opGrad "Tanh" _ [toT -> x] [dz] = [Just $ tanhGrad (tanh x) dz]
+opGrad "Sigmoid" _ [toT -> x] [dz] = [Just $ sigmoidGrad (sigmoid x) dz]
 
 opGrad "Concat" _ _ix [dy]
     -- Concat concatenates input tensors
@@ -947,6 +950,7 @@ numOutputs o =
         "ReluGrad" -> 1
         "Reshape" -> 1
         "Select" -> 1
+        "Sigmoid" -> 1
         "Size" -> 1
         "Slice" -> 1
         "SoftmaxCrossEntropyWithLogits" -> 2

tensorflow-ops/src/TensorFlow/Ops.hs

@@ -123,6 +123,8 @@ module TensorFlow.Ops
     , scalar'
     , shape
     , shape'
+    , CoreOps.sigmoid
+    , CoreOps.sigmoidGrad
     , CoreOps.sign
     , CoreOps.sign'
     , CoreOps.size

tensorflow-ops/tests/GradientTest.hs

@@ -368,6 +368,14 @@ testTanhGrad = testCase "testTanhGrad" $ do
         TF.gradients y [x] >>= TF.run
     V.fromList [1] @=? dx
 
+testSigmoidGrad :: Test
+testSigmoidGrad = testCase "testSigmoidGrad" $ do
+    [dx] <- TF.runSession $ do
+        x <- TF.render $ TF.vector  [0 :: Float]
+        let y = TF.sigmoid x
+        TF.gradients y [x] >>= TF.run
+    V.fromList [0.25] @=? dx
+
 testExpandDims :: Test
 testExpandDims =
   testCase "testExpandDims" $ do
@@ -681,6 +689,7 @@ main = defaultMain
             , testReluGrad
             , testReluGradGrad
             , testTanhGrad
+            , testSigmoidGrad
             , testExpandDims
             , testReshape
             , testPad