Week 3 - Solving second order ODEs

clear all;
clc
close all;

% inputs
b=0.05;
g=9.81;
l=1;
m=1;

theta_0=[0;3];
t_span=linspace(0,20,300);

[t,results]=ode45(@(t,theta_0) [theta_0(2);(-b/m)*theta_0(2)-(g/l)*sin(theta_0(1))],t_span,theta_0);

figure(1)
plot(t,results(:,1))
hold on
plot(t,results(:,2))
legend('angular_displacement','angular_velocity')


figure(2)
ct=1;
for i =1:length(t_span)
    x0=0;
    y0=0;
   
    x1=l*sind(results(i,1));
    y1=-l*cosd(results(i,2));

    plot([x0,x1],[y0,y1],[1 -1],[0,0],'linewidth',5)
    hold on 
    plot(x1,y1,'v','MarkerSize',30,'MarkerFaceColor','#EDB120')
    axis([-1 1 -1 1])
    grid on
    pause(0.2)
    M(ct)=getframe(gcf);  % collects all the figures in single window
    ct=ct+1;
   
end

movie(M)
videofile=VideoWriter('simple_pendulum.avi','uncompressed AVI');
open(videofile)
writeVideo(videofile,M)
close(videofile)