(  m2*l1*l2*( sin(u(1))*cos(u(3)) - cos(u(1))*sin(u(3)) )*u(4)^2  +  (m1+m2)*g*l1*sin(u(1))  +  k1*(l1^2)*u(2) + k2*l1*l2*(sin(u(1))*sin(u(3)) + cos(u(1))*cos(u(3)) ) * u(4)   )*(-1)