sap4是比较早的有限元程序，很多有限元程序都使用了这个（或稍作修改）作为初始代码。对于刚开始编写有限元程序的人来说很有用。-sap4 is relatively early in the finite element program, many finite element programs use this (or slight modifications) as the initial code. For starters, people who write the finite elem