功能: 统计矩阵里每个元素出现的次数

格式: 
[v, n] = DataCountByValue(a)
[v, n] = DataCountByValue(a, p)

a : 为待统计的矩阵变量
p : 数值,容错误差,默认1e-15 

v : 从小到大返回的唯一数值矩阵变量
n : 返回与v统计的数据出现次数

例子:
a =
[ 6.00000000000000    7.50000000000000    1.50000000000000    13.5000000000000
  13.5000000000000    9.00000000000000    9.00000000000000    1.50000000000000
  1.50000000000000    15.0000000000000    3.00000000000000    1.50000000000000
  9.00000000000000    6.00000000000000    6.00000000000000    7.50000000000000 ]
[v, n] = DataCountByValue(a)//回车得到如下结果
v =
[ 1.50000000000000
  3.00000000000000
  6.00000000000000
  7.50000000000000
  9.00000000000000
  13.5000000000000
  15.0000000000000 ]
n =
[ 4.00000000000000
  1.00000000000000
  3.00000000000000
  2.00000000000000
  3.00000000000000
  2.00000000000000
  1.00000000000000 ]
