例如：$ 质量守恒\qquad\qquad\qquad\qquad\qquad\qquad\qquad\qquad \frac{{\partial {\rho _{\text{m}}}}}{{\partial t}} + \frac{\partial }{{\partial {x_i}}}({\rho _{\text{m}}}{u_i}) = 0 \qquad\qquad\qquad\qquad\qquad\qquad\qquad\qquad\quad\;\;\;\;$
例如：$ 质量守恒\qquad\qquad\qquad\qquad\qquad\qquad\qquad\qquad \frac{{\partial {\rho _{\text{m}}}}}{{\partial t}} + \frac{\partial }{{\partial {x_i}}}({\rho _{\text{m}}}{u_i}) = 0 \qquad\qquad\qquad\qquad\qquad\qquad\qquad\qquad\quad;;;;$