杨氏定理Young`s Theorem

英文定义：

Let f be a differentiable function of n variables. If each of the crosspartials f "ij and f "ji exists andis continuous at all points in some open set S of values of (x1, ..., xn) then

f "ij(x1,..., xn) = f "ji(x1,..., xn) for all (x1,..., xn) in S.

中文定义：

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。即：

f "ij(x) = f "ji(x)