中文说明：自己实现的一维、二维DFT。优点：变换后的低频分量在中间，弥补了matlab库函数的不足（高频分量在中间）
English Description：
One dimensional and two-dimensional DFT realized by ourselves. Advantages: the transformed low-frequency component is in the middle, which makes up for the shortage of MATLAB library function (high-frequency component is in the middle)