参照Blazek博士的单元节点法准1-D 欧拉（Euler）方程程序，编写采用单元中心法的准1-D 欧拉（Euler）方程求解Laval缩放喷管的程序。(Referring to Dr. Blazek's element node method, the quasi 1-D Euler equation procedure is used to prepare the quasi 1-D Euler equation using th