功能: 计算神经网络GELU激活函数

格式: NetFunByGELU(x)

x : 为矩阵变量或者数值

说明:
1. 函数执行成功返回和x同纬度的矩阵变量

2. 本函数主要计算的原理如下
$$
\mathbf{netFunByGELU}(x_i) = \dfrac{x_i}{2}(1 + \tanh(\sqrt{\dfrac{2}{\pi}}(x_i + 0.044715 * x_i^3)))
$$

例子:
x =
[-0.73290256607947   -1.95092696112158    0.21744714338213    2.19789781453921
 -4.72275318588258    1.99957438581603    2.94959032789319   -4.31942455462153
 -6.10488919615973   -1.19050327068684   -6.38943656901337    2.98098757280083
 -2.76742173278119   -4.81647247463300   -3.72662812435377   -4.00467786914887 ]
y = netFunByGELU(x)//回车得到如下结果
y =
[-0.01663608712759   -2.0879328455E-05    0.16283262664741    2.19789448017402
  0.00000000000000    1.99955962670375    2.94959032434883    0.00000000000000
  0.00000000000000   -0.00208307258477    0.00000000000000    2.98098757025901
 -2.2561202456E-08    0.00000000000000   -2.6251729067E-13   -4.2237812977E-15 ]