说明：  多星座导航系统GDOP递推特性的仿真程序,程序主要是争对在现有系统中增加2颗现有星座的可见星时GDOP的变化情况组合仿真
(GDOP combination of changes in multi-constellation navigation system simulation GDOP recursive feature of the simulation program, the program mainly to fight for increased two existing constellation of visible stars in the existing system)