使用matlab软件，并利用三次样条插值法 求信号的包络线 源代码-Use matlab software, and use cubic spline interpolation method the signal envelope source code

提高算法的精确度，以及利用三次样条插值法与真实值做对比-Improve the accuracy of the algorithm, as well as cubic spline interpolation method to do comparison with the real value