利用DFT和IDFT计算x(n)和y(n) 的10点、15点、20点圆周卷积，然后与线形卷积结果画图比较-Calculated using DFT and IDFT x (n), and y (n) 10 points, 15 points, 20 points cyclic convolution, and then drawing comparison with the linear convolution result