http://www.pinggu.org/bbs/thread-801916-1-1.html

这个只能看stata的规定（见help）。

呵呵呵各顾各

用了help egen命令看到：
egen creates newvar of the optionally specified storage type equal to fcn(arguments).  Here fcn() is a function specifically written for egen, as documented below or as written by users.  Only egen functions may be used with egen, and conversely, only egen may be used to run egen functions.
注意看红色的部分，egen有单独的为它写的函数，而且这些函数只能用在egen里面！
再去看help gen，并没有这些！