$${\varphi }_{xY}(M)=E\{(x_{N+M}-{\mu }_x){(Y_N-{\mu }_Y)}^{\ast })\},$$

$$C_{xY}(M)=\{\begin{array}{ll}{\displaystyle \underset{N=0}{\overset{N-M-1.}{\sum }}\left(x_{N+M}-\frac{1.}{N}{\displaystyle \underset{我=0}{\overset{N-1.}{\sum }}{x}_{我}}\right)\left(Y_N^{\ast }-\frac{1.}{N}{\displaystyle \underset{我=0}{\overset{N-1.}{\sum }}{Y}_{我}^{\ast }}\right),}\hfill & M\ge 0,\hfill \\ C_{Yx}^{\ast }(-M),\hfill & M<0.\hfill \end{array}$$

$$\text{c（m）}=C_{xY}(M-N),M=1.,\dots ,2.N-1.$$