function I = simple_pendulum_internal_energy (theta)
% ’P�U‚èŽq‚Ì“à•”ƒGƒlƒ‹ƒM�[
    global len;
    global mass;
    global grav;
    global torque;
    
    U = mass*grav*len*(1-cos(theta));
    W = torque*theta;
    
    I = U - W;
end
