lpf

代码说明：

说明：  通过时域转换为频域，在频域中截取低频部分，去掉高频部分将结果再转换到时域以实现低通滤波的功能。(Through the time domain is converted to frequency domain, in the frequency domain low-frequency part of the interception, to remove high-frequency part of the results and then switch to the time domain in order to achieve low-pass filter function.)