input: fun x(t) t min & t max a df

T = t_max-t_min

fs = a*1/T

输入1：方程，xt；输入2，3：信号起始时间；输入4：选取的采样周期是信号长度倒数的倍数，

默认为50；输入5：频域分辨率，默认为0.3

输出频域信号和频域范围

为了提高fft的速度，频域信号长度是2的次方-　Input: fun x (t)　t min &　t max　a　df　 T = t_max-t_min　fs = a* 1/T　Input 1: Equation XT　input 2,3: signal start time　 input 4: select the sampling period is the reciprocal multiples of the signal length,　default is 50　input 5: frequency domain resolution, default is 0.3　of the output frequency domain signal and the frequency domain　in order to improve the speed of the FFT, the frequency domain signal length is a power of 2