Necessary and sufficient conditions for $n$-times Fr\'echet differentiability on ${\mathcal S}^p,$ $1 <p<\infty.$

Abstract

Let $1<p<\infty$ and let $n\geq 1$. It is proved that a function $f:{\mathbb R}\to {\mathbb C}$ is $n$-times Fr\'echet differentiable on ${\mathcal S}^p$ at every self-adjoint operator if and only if $f$ is $n$-times differentiable, $f',f'',\ldots,f^{(n)}$ are bounded and $f^{(n)}$ is uniformly continuous.