功能: 计算神经网络SoftSign激活函数

格式: netFunBySoftSign(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
$$\mathbf{netFunBySoftSign}(x_i) = \dfrac{x_i}{1 + |x_i|}$$

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 = netFunBySoftSign(x)//回车得到如下结果
y =
[-0.42293351076142   -0.66112343234008    0.17860910394684    0.68729457349965
 -0.82525893262933    0.66661936949166    0.74680918348981   -0.81200974095380
 -0.85925185145174   -0.54348390464331   -0.86467168495723    0.74880604832020
 -0.73456648314714   -0.82807448941583   -0.78843268950067   -0.80018693986990 ]