From 06a22ca5bd0e34689d4fcff0cdd6edfd1ee76d2d Mon Sep 17 00:00:00 2001
From: Benoit Steiner <benoit.steiner.goog@gmail.com>
Date: Fri, 17 Jul 2015 09:29:00 -0700
Subject: Added support for sigmoid function to the tensor module

---
 unsupported/Eigen/CXX11/src/Tensor/TensorBase.h    |  6 +++++
 .../Eigen/CXX11/src/Tensor/TensorFunctors.h        | 30 ++++++++++++++++++++++
 2 files changed, 36 insertions(+)

(limited to 'unsupported/Eigen')

diff --git a/unsupported/Eigen/CXX11/src/Tensor/TensorBase.h b/unsupported/Eigen/CXX11/src/Tensor/TensorBase.h
index 71f69b568..0e5e4b426 100644
--- a/unsupported/Eigen/CXX11/src/Tensor/TensorBase.h
+++ b/unsupported/Eigen/CXX11/src/Tensor/TensorBase.h
@@ -116,6 +116,12 @@ class TensorBase<Derived, ReadOnlyAccessors>
       return unaryExpr(internal::scalar_tanh_op<Scalar>());
     }
 
+    EIGEN_DEVICE_FUNC
+    EIGEN_STRONG_INLINE const TensorCwiseUnaryOp<internal::scalar_sigmoid_op<Scalar>, const Derived>
+    sigmoid() const {
+      return unaryExpr(internal::scalar_sigmoid_op<Scalar>());
+    }
+
     EIGEN_DEVICE_FUNC
     EIGEN_STRONG_INLINE const TensorCwiseUnaryOp<internal::scalar_exp_op<Scalar>, const Derived>
     exp() const {
diff --git a/unsupported/Eigen/CXX11/src/Tensor/TensorFunctors.h b/unsupported/Eigen/CXX11/src/Tensor/TensorFunctors.h
index 14ffd5c93..1a23a9fa0 100644
--- a/unsupported/Eigen/CXX11/src/Tensor/TensorFunctors.h
+++ b/unsupported/Eigen/CXX11/src/Tensor/TensorFunctors.h
@@ -13,6 +13,36 @@
 namespace Eigen {
 namespace internal {
 
+
+/** \internal
+  * \brief Template functor to compute the sigmoid of a scalar
+  * \sa class CwiseUnaryOp, ArrayBase::sigmoid()
+  */
+template <typename T>
+struct scalar_sigmoid_op {
+  EIGEN_EMPTY_STRUCT_CTOR(scalar_sigmoid_op)
+  EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE T operator()(const T& x) const {
+    const T one = T(1);
+    return one / (one + std::exp(-x));
+  }
+
+  template <typename Packet>
+  inline Packet packetOp(const Packet& x) const {
+    const Packet one = pset1<Packet>(1);
+    return pdiv(one, padd(one, pexp(pnegate(x))));
+  }
+};
+
+template <typename T>
+struct functor_traits<scalar_sigmoid_op<T> > {
+  enum {
+    Cost = NumTraits<T>::AddCost * 2 + NumTraits<T>::MulCost * 6,
+    PacketAccess = packet_traits<T>::HasAdd && packet_traits<T>::HasDiv &&
+                   packet_traits<T>::HasNegate && packet_traits<T>::HasExp
+  };
+};
+
+
 // Standard reduction functors
 template <typename T> struct SumReducer
 {
-- 
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