From 52dcf4801dddf05df3ddef238895cabbc6c4384a Mon Sep 17 00:00:00 2001
From: Azat <davletag@mail.ru>
Date: Thu, 3 Dec 2015 13:56:48 +0300
Subject: [PATCH] sigmoid fix (cu)

Previous implementation caused FP overflow for x less than -90
---
 src/caffe/layers/sigmoid_layer.cu | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/caffe/layers/sigmoid_layer.cu b/src/caffe/layers/sigmoid_layer.cu
index 184c61ede83..8a4ea6616e0 100644
--- a/src/caffe/layers/sigmoid_layer.cu
+++ b/src/caffe/layers/sigmoid_layer.cu
@@ -8,7 +8,7 @@ namespace caffe {
 template <typename Dtype>
 __global__ void SigmoidForward(const int n, const Dtype* in, Dtype* out) {
   CUDA_KERNEL_LOOP(index, n) {
-    out[index] = 1. / (1. + exp(-in[index]));
+    out[index] = 0.5 * tanh(0.5 * in[index]) + 0.5;
   }
 }