功能: 计算神经网络SELU激活函数

格式: netFunBySELU(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
$$
\begin{aligned}
\alpha &=1.67326324235437728
\\
\beta &= 1.05070098735548049
\\
\mathbf{netFunBySELU}(x_i) &=\begin{cases}
\beta\alpha(\exp(x_i) - 1)&,x_i <0
\\
return \beta x_i&,x_i\geq 0
\end{cases}
\end{aligned}
$$
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 = netFunBySELU(x)//回车得到如下结果
y =
[-0.91331107884456   -1.50819914453513    0.22847192824923    2.30933340384280
 -1.74246866476946    2.10095478146763    3.09913746981155   -1.73470336512485
 -1.75417538853678   -1.22351724423009   -1.75514713683123    3.13212658603625
 -1.64764890767509   -1.74386701123715   -1.71577508016757   -1.72604890714353 ]