说明：  选择不同的两个函数做卷积运算，可供选择的函数有矩形窗函数，锯齿波函数和sinc函数，也可自行选择其他窗，观察选取函数的波形。
(Choose a different function to do convolution function to choose a rectangular window function, ramp function and the sinc function, to choose the other window, observe the waveform of the selected function.)