文中探讨的任意空间六面体协调单元，能保证单元节点上的函数，一阶导数及其二、三阶混合导数是连续的。

• A third-order polynomial based on three-dimensional Cartesian coordinates (x, y, z) is adoped as the element interpolating function to make sure that first derivatives and second and third mixed derivatives of the variable functions over the entire domain are continuous.