中文摘要：

提出了二阶椭圆问题的一个混合变分形式，同时证明了Rariart-Thomas元的各向异性插值性质，并给出了单元的对二阶问题的最优误差估计．

英文摘要：

A mixed formulation for second order elliptic problem with anisotropic meshes is proposed. The anisotropic interpolation property of the Rariart-Thomas element is proved under the general framework and the optimal error estimate is obtained.