FFT和IFFT，时析型FFT是将序列逐次奇偶对分，奇数号排成一子序列，偶数号排成一子序列，各子序列的长度为N/2，-FFT and IFFT, the analysis type FFT is a sequence of successive parity pairs of points arranged in a sub-sequence, odd and even number of numbers arranged in a promoter sequence, each sub-seq