功能: 计算神经网络SLine激活函数

格式: netFunBySLine(x, a)

x : 为矩阵变量或者数值
a : 为数值或者1*1的矩阵变量

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
$$\mathbf{netFunBySLine}(x_i, a_i) = \mathbf{Sign}(x_i)\dfrac{x_i^2}{1 + |a_ix_i|}$$

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 = netFunBySLine(x, 3.6)//回车得到如下结果
y =
[-0.14763052505246   -0.47438066968274    0.02652176490628    0.54202430171967
 -1.23900163007431    0.48768841048647    0.74881131359651   -1.12734194589374
 -1.62200013505204   -0.26813252116936   -1.70089775404284    0.75746878488600
 -0.69860621068541   -1.26495591159198   -0.96336645716992   -1.04025497400722 ]