ode for simple pendulum without damping

% ODE for simple pendulum (assignment)

clear all
close all
clc

%Given

g=9.81;
l=0.5;
m=0.5;

%Initial condition

theta = [0;5];

%Time span

t_span = linspace(0,8,500);

%solving ode

[t,results] = ode45(@(t,theta) ode_func_nd(t,theta,g,l,m),t_span,theta);

%plot

figure(1)                  %part 1 plot

plot(t,results(:,1),\'color\',\'b\')
hold on
plot(t,results(:,2),\'color\',\'r\')

%%Animating the simple pendulum

figure (2)

angle = results(:,1);

Xa1=1.5;
Ya1=2;

Xa2=-1.5;
Ya2=2;

%Creating loop

ct=1;

for i=1:length(t)
    
    x0 = 0;
    y0 = 2;
    
    x1 = l*sin(angle(i));
    y1= -l*cos(angle(i));
    
    r = 0.15;
    xc = x1;
    yc = y1;

    theta_c = linspace(0,2*pi);
    x_c = r*cos(theta_c) + xc;
    y_c = r*sin(theta_c) + yc;
    
    plot([x0 x1],[y0 y1],[Xa1 Xa2],[Ya1 Ya2],x_c,y_c,\'linewidth\',2)
   
    
   
    % plot([Xa1 Xa2],[Ya1 Ya2])
    
    axis([-2 2 -2 3])
    pause(0.03)
    
    M(ct)=getframe(gcf);
    
    ct=ct+1;
    
end

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

For function to solve ODE

function [ansode] = ode_func_nd(t,theta,g,l,m)

  theta1 = theta(1);
  theta2 = theta(2);
  dtheta1_dt = theta2;
  dtheta2_dt = -((g/(l*m))^2) *sind(theta1);
  ansode = [dtheta1_dt;dtheta2_dt];
  
end

%%link for the animation%%

https://drive.google.com/open?id=1zFJAYy4SsZ_Ue-YCfpDMJYkF3mKcDdAn