if is_peak and up_point != -1 and i - up_point > 4: wave_peaks.append((up_point, i))解释一下这段代码

This code block appends a tuple to a list called `wave_peaks` if the following conditions are met:

- `is_peak` is `True` (meaning the current value is a peak)
- `up_point` is not equal to `-1` (meaning there is a recently found trough to compare this peak to)
- The difference between the index of the current peak (`i`) and the index of the most recent trough (`up_point`) is greater than 4.

The tuple that is appended to `wave_peaks` contains the indices of the beginning and end of the wave (the trough and peak, respectively).