说明：  Gnuplot是一个命令行的交互式绘图工具,用户通过输入命令，可以逐步设置或修改绘图环境，并以图形描述数据或函数，使我们可以借由图形做更进一步的分析。
(Gnuplot is a command-line interactive drawing tools, by entering the command, the user can gradually set or modify the drawing environment, and a graphic description of the data or function, so we can do further analysis by graphic.)