Week 3 - Solving second order ODEs

%ODE_MAIN 

clear all
close all
clc

b=0.05;
g=9.81;
l=1;
m=1;
A_d=0;
A_v=3;
t=0;

% Initial condition;

theta_0 = [0;3];

% 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);
figure(1)
plot(t,results(:,1))
hold on
plot (t,results(:,2))
ylabel('plot')
xlabel('plot')

x0=0;
y0=0;

ct=1;
for i=1:length(t_span)

x1=1*sin(results(i,1));
y1=-1*cos(results(i,1));

figure(2)
plot([x0 x1],[y0 y1]);
hold on
plot(x1,y1,'.','MarkerSize',40)
axis([-2 2 -2 2])
hold off

M(ct)=getframe(gcf);
ct=ct+1;

end

movie (M)
videofile = VideoWriter('fwi.avi');
open(videofile)
writeVideo(videofile,M)
close(videofile)

%ODE_FUNC

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/l)*sin(theta1);
dtheta_dt = [dtheta1_dt; dtheta2_dt];

end

https://drive.google.com/file/d/1xG2EIGsMmNOSemJUq5fsJ_Gv8pG29X2K/view?usp=sharing

Explanation:

Errors faced while programming.

Error 1: Forgot to inert the @ symbol in ode45(@(t,theta)ode_func(t,theta,b,g,l,m),t_span,theta_0);

Error 2:Forgot to mention the * symbol for x1 and y1. Here * is used for multiplication.

x1=1*sin(results(i,1));
y1=-1*cos(results(i,1));