说明：  求解抛物线方程的显式法，编译example_01生成可执行文件，输入example_01 inp.txt.边界条件的中心差分离散，编译example_02a.f，输入example_02ainp.txt.边界条件的向前差分离散example_02b.f,输入example_02binp.txt.
(Explicit solving parabolic equation method, the compiler generates an executable file example_01, enter example_01 inp.txt. The central difference discrete boundary conditions, compile example_02a.f, enter example_02ainp.txt. Boundary forward difference discrete example_02b.f, input example_02binp.txt.)