solving second order ODE and animation of pandulum

Here in this program I solve second order ODE for pendulum. also plot graph of plot vs time.

how oscillation would change with the time.

Here i solve above given equation by creating function for it.

Creat animation for for the same ODE how it work when length of thred is 1m, mass = 1Kg,

and b = 0.5.

Animation video link: https://youtu.be/tnXF57sZJzM

clear all
close all
clc

b = 0.5;
g = 9.81;
l = 1;
m = 1;

%initial condition
theta_0 = [0;3];

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

%solve ODE
[t, results] = ode45(@(t,theta) ode_function(t,theta,b,g,l,m), t_span, theta_0)
ct = 1
for i = 1:1
plot(t, results(:,1))
hold on 
plot(t, results(:,2))
xlabel(\'time\')
ylabel(\'plot\')
ct = ct + 1;
end
figure(ct)

x = results(:,1);
%animation 
%origine
O = [0,0];
axis([-1.5 1.5 -1.5 1.5]) %the limits of the plot
grid on
count = 1;
%loop for animation
for i = 1:length(t)
    
    %mass point
    P = l*[sin(x(i,1)) -cos(x(i,1))];
    
    %circle in origin
    O_circle = viscircles(O,0.01);
    
    %pendulum
    pend = line([O(1) P(1)], [O(2) P(2)]);

    %ball
    ball = viscircles(P,0.05);
    
    %time interval to upadate the plot
    pause(0.0001);
    R(count) = getframe(gcf);
    count = count + 1;
    
    %delete previous object if it is not final loop
    if i<length(t)
        delete(pend);
        delete(ball);
        delete(O_circle);
    end
    
end

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