功能: 按多个列索引获取矩阵列并组成新矩阵

格式: GetColByIndex(a, index)

a    : 获取列的源矩阵变量
index: 存储列索引的矩阵变量, 里面元素的值必须在1到a的列数之间

例子:
a =
[ 0.97863628574583    28.7926793698187    7.10279222908560    20.7065467074078
  4.06545013378628    18.8391721150089    16.2087951256935    29.8725344007241 ]

b = [1, 3, 3, 2];

c = GetColByIndex(a,b)//执行得到如下结果
c =
[ 0.97863628574583    7.10279222908560    7.10279222908560    28.7926793698187
  4.06545013378628    16.2087951256935    16.2087951256935    18.8391721150089 ]