If the path corresponds to a file, this function checks whether file size equals 0.
如果路径与文件对应，此函数将检查文件的大小是否等于0。
2
Suppose we were to graph a household's consumer spending as a function of cash-on-hand, which equals current income plus liquid assets, holding constant expected future income.
So if you have a certain number of neutrons produced and that equals the number of losses your K effective would be one which is the desirable function.