凸函数的又一等价命题

Another Equivalent Proposition on Convex Function

裴礼文［1］给出了f(x)为区间I上 的凸函数的一个必要条件，该文证明当I为开区间时，其充分性亦正确。

PEI Liwen［1］has given a necessary c ondition that a function f(x) defined at an interval I is a convex function.This paper proves its sufficiency correct when I is an open interval.