clear

clc

close all

fs=200;

t=(1/200:1/200:30)';

signal=sin(2*pi*0.1*t);

LL=1:1:length(t);

figure(1)

plot(LL,signal)

zero_indices = []; % 存储最靠近0的点的索引

start_indices = []; % 存储开始点的索引

end_indices = []; % 存储结束点的索引

for i = 2:length(signal)-1 % 从第2个点开始，到倒数第2个点结束

% 检查当前点及其相邻点，确保中间点是极小值

if abs(signal(i)) < abs(signal(i-1)) && abs(signal(i)) < abs(signal(i+1))

zero_indices = [zero_indices; i];

% 检查零点右侧的点是正还是负，以确定是开始点还是结束点

if signal(i+1) > 0

start_indices = [start_indices; i];

elseif signal(i+1) < 0

end_indices = [end_indices; i];

end

end

end

% 绘制图像

figure(1)

plot(LL, signal)

hold on

plot(zero_indices, signal(zero_indices), 'ro', 'MarkerSize', 10)

plot(start_indices, signal(start_indices), 'go', 'MarkerSize', 10)

plot(end_indices, signal(end_indices), 'bo', 'MarkerSize', 10)

legend('Signal', 'Zero Points', 'Start Points', 'End Points')

hold off