Definition:Continuously Differentiable/Real-Valued Function/Open Set
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Definition
Let $U$ be an open subset of $\R^n$.
Let $f: U \to \R$ be a real-valued function.
Then $f$ is continuously differentiable in the open set $U$ if and only if:
- $(1): \quad f$ is differentiable in $U$.
- $(2): \quad$ the partial derivatives of $f$ are continuous in $U$.
This can be denoted:
- $f \in \map {\CC^1} {\mathbb X, \R}$
Also see
- Definition:Differentiability Class for insight into the notation $\map {\CC^1} {U, \R}$