Let $ 1<p< \infty $ and $ f: \mathbb{R}^{n} \rightarrow \mathbb{R} $ , $ f(x)=(\sum_{j=1}^{n} |x_{j}|^{p})^{\frac{1}{p}} $ . At what point f is differentiable ?
I have thought that $ f $ is not differentiable at $0$ and at all negative points . So in my sense, $f$ is differentiable at all $x \in \mathbb{R}^{n} , x>0 $ . But i am not sure. can anyone help me. Thanks.
