用矩阵的正定性判定多元函数极值的存在性

Determination on the Existence of Extremum in Multivariable Functions by the Positive Definiteness of Their Matrices

本文提出了一种判断多元函数极值存在性的方法。用这种方法不仅能判断二元函数极值的存在性，而且能判断二元以上的函数极值的存在性，弥补了教材在这方面的不足，方法简便易学，便于掌握。

A method to determine the existence of extremum in multivariable functions is presented. With this method, not only in bivariate functions, but also in multivariable functions,can the existence of extremum be determined. The method is easy to learn and convenient to use.