说明：  双矩形脉冲的正反傅里叶变换 (1) 画出以上式子所定脉冲的时域波形; (2)画出信号的振幅谱 abs(sf);(3) 将第二步所得的频谱求傅里叶反变换，并画出其波形，并与原始信号对比;
(Positive and inverse Fourier transform of double rectangular pulses (1) draw the above formula set by the pulse waveform; (2) draw the signal amplitude spectrum of ABS (SF); (3) the frequency spectrum obtained by the second step is inverse transform, and its waveform is drawn and compared with the original signal.)