中文说明：
程序名称：gm21.m GM(2,1)模型
程序功能：利用GM(2,1)模型进行预测
程序编写：mongvi
开发指导：刘思峰教授
程序发布：南京航空航天大学灰色系统研究所
English Description：
Program name: gm21. M GM (2, 1) model program features: using GM (2, 1) model to forecast programming: mongvi development direction: professor nelson published applications: nanjing university of aeronautics and astronautics institute of grey system