平面问题等参单元的有限元程序设计，平面弹性力学问题的四结点四边形有限单元法。输出结果为各结点位移和单元中心点应力分离及主应力。-This is finite element programming of isoparametric element on plane problem, it solves the four-node quadrilateral plane elasticity problems using finite element method. The output can be the displacements for each node, the unit strain and the cental main strain.