说明：  C#快速傅立叶变换，输入为时域的实部和虚部，输出为频域的虚部和实部，并可以选择逆变换或返回模和相位
(C# Fast Fourier Transform, enter the domain too real and imaginary parts, the output for the frequency domain of the imaginary part and real part, and can choose or return inverse transform modulus and phase)