计算信号循环谱的函数：

这个函数用来计算数字调制信号的循环谱图，结果存放在sxf中，surf和shading interp这两个函数配合使用就可以得到信号的循环谱图-Calculate the signal cyclic spectrum function:

This function is used to calculate the cycle spectrum of digitally modulated signals, the result stored in the sxf in, surf, and shading interp these two functions can be used in conjunction with the cycle of the signal spectrum