get_ft

代码说明：

   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)