说明：  这是一个标准二维格子Boltzmann程序，边界处理采用周期边界。该程序是NDSU Alexander Wagner 为教学目的所写的教学程序，其中包含的一些C++用法比较特别，但可读性高且实用。
(This is a standard two dimensional lattice Boltzmann program with periodic boundary conditions that should perform reasonably efficiently.It has been written for teaching purposes by Alexander Wagner at NDSU (March 2003))