说明：  用Matlab实现求泊松方程数值解的有限元法。 泊松方程是数学中一个常见于静电学、机械工程和理论物理的偏微分方程。
(Using Matlab to achieve the requirements of the finite element method for the numerical solution of the Poisson equation. Poisson equation is common in mathematics partial differential equations of electrostatics, mechanical engineering and theoretical physics.)