给定两个序列 x(n)=[2,1,1,2],h(n)=[1,-1,-1,1,]， 。首先直接在时域计算两者的线性卷积；然后用FFT快速计算二者的线性卷积，验证结果。-Given two sequences, a.First directly evaluated both linear convolution in time domain Then using FFT fast calculation of the two linear convolution, the verification