Generalized Covariant Derivative with Respect to Time in Flat Space (II): Lagrangian Description

The previous paper reported a new derivative in the Eulerian description in flat space-the generalized covariant derivative of generalized Eulerian component with respect to time. This paper extends the thought from the Eulerian description to the Lagrangian description: on the basis of the postulate of covariant form invariability in time field, we define a new derivative in the Lagrangian description in flat space-the generalized covariant derivative of generalized Lagrangian component with respect to time. Besides, the covariant differential transformation group is set up. The covariant form invariability of Lagrangian space-time is ascertained.