Week 3 - Solving second order ODEs

YouTube Link
https://youtu.be/KENwGCXh254


Main Code:
clear all
close all
clc
 b = 0.05;
 g = 9.81;
 l = 1;
 m = 1;
 
 %initial conditions
 theta_0 = [0;5];
 %time points
 t_span = linspace(0,10,500);
 %solve ode
 [t, results] = ode45(@(t, theta) ode_func(t, theta, b, g, l, m), t_span, theta_0);  
 %ODE45 is a pre-installed solver which performs a direct numerical integration of a set of differential equations. Hence, here we are giving the angular displacement and time interval for each angular displacement the time interval. And in function we are giving the values and the time span and angle.
 plot(t, results(:,1))
 hold on
 plot(t, results(:,2))
 ylabel('velocity')
 xlabel('time')
 
 ct = 1;
 for i = 1:length(results(:,1))
     x0 = 0
     y0 = 0
     x1 = 1*sind(results(i,1));
     y1 = 1*cosd(results(i,1));
     plot([-1 1], [0,0],'linewidth',3,'color','g');
     hold on
     line([x0 x1], [y0 y1],'linewidth',3,'color','b');
     hold on
     
     grid on 
     axis([-1.5 1.5 0 1.5])
     pause(0.0001);
     hold off
     M(ct) = getframe(gcf);
     ct = ct + 1;
 end
 movie(M)
 videofile = VideoWriter('pendulum_ode.avi','uncompressed AVI')
 open(videofile)
writeVideo(videofile,M)
close(videofile)


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)*sind(theta1);
dtheta_dt = [dtheta1_dt; dtheta2_dt];
end




%I'm facing trouble with the inverted pendulum. I have tried many ways but was unable to solve it. Could you explain where I'm facing the issue?