The first peak is menstruation.

It's in the program.

corr 1=autocorr(z( 1，)，numel(z( 1，)- 1)；

Figure (2)

clf

Drawing (corr 1)

Common periodic signals include sinusoidal signals, pulse signals and their rectification, differentiation and integration. This signal can be called a simple signal. Their characteristic is that there will not be more than two extreme points in a period, and the periodicity is obvious. For this kind of signal with periodic characteristics, it is relatively simple to judge whether it is periodic, and the methods of periodic measurement are very mature and perfect, such as zero-crossing detection and pulse shaping.

Signal division

The signal can be analog or digital. If it is continuous time and continuous value, then it is an analog signal. If it is discrete time and discrete value, then it is a digital signal. In addition to this distinction, signals can also be divided into periodic or aperiodic.

The method of distinguishing periodic signals from aperiodic signals: 1. The frequency spectrum of periodic signals is discrete, while the frequency spectrum of quasi-periodic signals is continuous. 2. Because the periodic signal can be expressed by a set of trigonometric functions with integer times frequency, it is a discrete frequency point in the frequency domain. After Fourier transform, the quasi-periodic signal tends to infinity, so it becomes continuous in frequency spectrum.