用有限元方法解偏微分方程的算例。区域是[0,1]*[0,1]的正方形区域，区域剖分网格是标准正方形。区域剖分、节点计算、转化成代数方程求解，结果画图显示及txt结果输出，每一步都很详细。-Two-dimensional numerical example of using the finite element method for solving partial differential equations . Region is a [0,1]* [0,1] of the square region, a square region of a standard mesh grid. Regional split, node calculation, converted into algebraic equations, the results display and txt file result output, each step is very detailed.