产生0-4之间，间隔5秒-20秒之间的随机阶跃信号。

clear;
clc;
close all;
format short

n = 4;
i = 0;
y_1 = rand(1,1)*4;
figure
title('随机信号生成中...');
for i=1:800
    line([i-1,i],[y_1,y_1],'LineWidth',2);
    y = rand(1,1)*4
    line([i,i],[y_1,y],'LineWidth',2);
    hold on;
    grid on;
    y_1 = y;
    str = ['随机信号生成中,当前间隔时间：',num2str(5+rand(1,1)*(20-5)),'s。'];
    pause(5+rand(1,1)*(20-5));
    title(str)
end