title: How can I solve this third order equation using the ODE45 function?
body: <p>When I convert the third order ODE into a system of first order ODEs, I got this:</p>
  
  <pre><code>x1' = x2;
  x2' = x3;
  x3' = R1*x1+R2*x2-alpha*x3;
  x4' = 1;
  
  where
  x4 = t; 
  R1 = -0.000001*(1-cos(theta*x4))-theta*sin(theta*x4)+1;
  R2 = -(1-cos(theta*x4));
  </code></pre>