Solving Second Order ODE defining a pendulum

Youtube link: https://youtu.be/XlxJw6TyJ_8

pendulum motion code

clear all
close all
clc

b=0.05;
g=9.81;
l=1;
m=0.1;

%initial condition
theta_0 = [0;3];

%time points
t_span = linspace(0,20,500);

%solve ode
[t, results] = ode45(@(t,theta) ode_func(t,theta, b,g,l,m),t_span, theta_0);

figure(1)
plot(t,results(:,1))
hold on
plot(t,results(:,2))
ylabel(\'Plot\')
xlabel(\'time\')

%animation
figure(2)

theta = results(:,1);

ct = 1;
for i = 1:length(t_span)
    % coordinates
    x0 = 0;
    y0 = 0;
    x1 = l*sind(theta(i,1));
    y1 = -l*cosd(theta(i,1));
    
    %plotting
    plot([x0 x1],[y0 y1],\'-o\',\'linewidth\',7,\'color\',\'b\');

    axis([-0.1 0.1 -2 0.5])
    M(ct) = getframe(gcf);
    ct = ct+1;
end

movie(M)
videofile = VideoWriter(\'pendulum_motion.avi\',\'Uncompressed AVI\');
open(videofile)
writeVideo(videofile,M)
close(videofile)

ode function code

function [dtheta_dt] =  ode_func(t,theta, b,g,l,m)

theta1 = theta(1)
theta2 = theta(2)
dtheta1_dt = theta2;
dtheta2_dt = -(b/m)*theta2 - (g/1)*sin(theta1);
dtheta_dt = [dtheta1_dt;dtheta2_dt];
end

plot generated