https://medium.com/%E9%9B%BB%E8%85%A6%E8%A6%96%E8%A6%BA/%E5%82%85%E5%88%A9%E8%91%89%E8%BD%89%E6%8F%9B-fourier-transform-ft-%E7%B0%A1%E4%BB%8B-7f5458851992
https://medium.com/%E9%9B%BB%E8%85%A6%E8%A6%96%E8%A6%BA/%E5%82%85%E5%88%A9%E8%91%89%E8%BD%89%E6%8F%9B-fourier-transform-ft-%E7%B0%A1%E4%BB%8B-7f5458851992