Lagrangian

$ L(q(t),\dot q(t),t)

作用 (action)

$ S=\int_{t_i}^{t_F}L dt

運動方程式

$ {\bf F}=m\ddot{\bf x}

$ \frac d{dt}\frac{\partial L}{\partial \dot q_i}-\frac{\partial L}{\partial q_i}=0