在学习有限元课程时做的一个作业，用C/C++编程求解一个简单的有限元问题，可以作为有限元学习的编程实例，以更好地理解有限元理论(A homework done while studying the finite element course. Solving a simple finite element problem with C / C ++ programming can be used as a programming example for finite element learning to better understand the finite element theory.)