楊氏定理

楊氏定理：如果N個變數的函式f(X)有連續二階偏微分，則交叉偏微分（混合偏微分）相等。

楊氏定理Young`s Theorem

英文定義：

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

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

中文定義：

即：

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