杨氏定理:如果N个变量的函数f(X)有连续二阶偏微分,则交叉偏微分(混合偏微分)相等. 杨氏定理Young`s Theorem 英文定义: Let be a differentiable function of variables. If each of the crosspartials " and " exists andis continuous at all points in some open set of values of ( 1, ..., ) then " ( 1,..., ) = " ( 1,..., ) for all ( 1,..., ) in . 中文定义: 即: " ( ) = " ( ).杨氏定理Young`s Theorem 英文定义: Let be a differentiable function of variables. If each of the crosspartials " and " exists andis continuous at all points in some open set of values of ( 1, ..., ) then " ( 1.., ) = " ( 1.., ) for all ( 1.., ) in . 中文定义: 即: " ( ) = " ( )