function no_result = run_forced()
   
   global omega A g L
   
   %initial conditions
   x0=0.0;
   v0=0.0;
   t0=0.0;
   
   %timing
   dt = 0.1
   duration = 150
   N_steps = duration/dt
   
   % forcing function A*sin(omega*t)
   omega = 1.0; % 1.0 is resonant if L=g.
   A = 0.01;
   
   y = rk2([x0,v0], t0, dt, N_steps, 'pendulum2');
   theta = y(:,1);
   theta_dot = y(:,2);
   
   energy = g*L*(1 - cos(theta)) + 0.5*(L*theta_dot).^2;
   time = t0:dt:duration;
   hold off
   plot(time, theta,'r')
   hold on
   plot(time, energy,'b')
   hold off
