功能: 计算两个序列的互相关性

格式: 
[v, n] = XCorr(x, y)

x : 矩阵变量
y : 矩阵变量

r : 计算的互相关序列向量
n : 滞后索引

说明:
1. 本函数计算两个序列的互相关性,原理如下
$$
\begin{cases}
v &= \mathbf{XCorr}(x,y)
\\
\\
v_k &=\sum_{i=-\infty}^\infty x_i y_{i+k}
\end{cases}
$$

2. 不要求x,y维度一致

例子:
x = 1 : 6;
y = sin(x);
[v,n] = XCorr(x,y)//回车得到如下结果
v =
[-0.27941549819892
 -1.51775527106099
 -3.51289753923098
 -5.36691979934111
 -6.31164463262555
 -6.41489848110210
 -4.56224384218617
  2.32638773017818
  8.75909112171920
  9.66313948499357
  5.04882590884738 ]
n =
[-5.00000000000000
 -4.00000000000000
 -3.00000000000000
 -2.00000000000000
 -1.00000000000000
  0.00000000000000
  1.00000000000000
  2.00000000000000
  3.00000000000000
  4.00000000000000
  5.00000000000000 ]
