利用matlab实现功率谱估计中的间接法，不是通过函数调用实现的，是根据算法的思想，一步一步实现的，文件夹中还有实现自相关的算法-Using matlab to achieve the indirect method of power spectrum estimation, not by function calls, is based on the idea of ​ ​ the algorithm, step by step, the folder also auto-correlation algorithm