摘要
对于二次可微实函数给出判别凸性的充要条件，与一阶条件相比，比较简单，也便于运用，至少对ｎ元二次函数是这样。
The necessary and sufficient conditions of judging the convexity of differential second order real function are presented below.The conditions presented are easier to be applied and simpler than those of judging first order conditions.
