Let $1<p<\infty$ and let $n\geq 1$. It is proved that a function $f:{\mathbb R}\to {\mathbb C}$ is $n$-times Fréchet 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.
Let $W$ be a finite reflection group. A $W$-invariant function of class~$C^{\infty}$ may be expressed as a functions of class $C^{\infty}$ of the basic invariants. In finite class of differentiability, the situation is not this simple. Let~$h$ be the greatest Coxeter number of the irreducible components of $W$ and $P$ be~the Chevalley mapping, if $f$ is an invariant function of class $C^{hr}$, and $F$ is the function of invariants associated by $f=F\circ P$, then $F$ is of class $C^r$. However if~$F$ is of class $C^r$, in general $f=F\circ P$ is of class $C^r$ and not of class $C^{hr}$. Here w…
We establish, for $1 < p < \infty$, higher order $\mathcal{S}^p$-differentiability results of the function $φ: t\in \mathbb{R} \mapsto f(A+tK) - f(A)$ for selfadjoint operators $A$ and $K$ on a separable Hilbert space $\mathcal{H}$ with $K$ element of the Schatten class $\mathcal{S}^p(\mathcal{H})$ and $f$ $n$-times differentiable on $\mathbb{R}$. We prove that if either $A$ and $f^{(n)}$ are bounded or $f^{(i)}, 1 \leq i \leq n$ are bounded, $φ$ is $n$-times differentiable on $\mathbb{R}$ in the $\mathcal{S}^p$-norm with bounded $n$th derivative. If $f\in C^n(\mathbb{R})$ with bounded $f^{(n)…
Let $\mathcal{L}(X;Y)$ be the space of bounded linear operators from a Banach space $X$ to a Banach space $Y$. Given an operator-valued function $u:\mathbb{R}_{\geq 0}\rightarrow \mathcal{L}(X;Y)$, suppose that every orbit $t\mapsto u(t)x$ has a regularity property (e.g. continuity, differentiability, etc.) on some interval $(t_x,\infty)$ in general depending on $x\in X$. In this paper we develop an abstract set-up based on Baire-type arguments which allows, under certain conditions, removing the dependency on $x$ systematically. Afterwards, we apply this theoretical framework to several diffe…
We study interior $L^p$-regularity theory, also known as Calderon-Zygmund theory, of the equation \[ \int_{\mathbb{R}^n} \int_{\mathbb{R}^n} \frac{K(x,y)\ (u(x)-u(y))\, (φ(x)-φ(y))}{|x-y|^{n+2s}}\, dx\, dy = \langle f, φ\rangle \quad φ\in C_c^\infty(\mathbb{R}^n). \] For $s \in (0,1)$, $t \in [s,2s]$, $p \in [2,\infty)$, $K$ an elliptic, symmetric, Hölder continuous kernel, if $f \in \left (H^{t,p'}_{00}(Ω)\right )^\ast$, then the solution $u$ belongs to $H^{2s-t,p}_{loc}(Ω)$ as long as $2s-t < 1$. The increase in differentiability is independent of the Hölder coefficient of $K$. For example, …
Point Feature Descriptor via Directional Partition of Unity on Maps
Faculty of Applied Science, Ho Chi Minh City University of Technology(胡志明市理工大学应用科学学院);Department of Applied Mathematics, Faculty of Applied Science, Ho Chi Minh City University of Technology(胡志明市理工大学应用科学学院应用数学系);Vietnam National University Ho Chi Minh City(越南国家大学胡志明市分校)
On best approximation by multivariate ridge functions with applications to generalized translation networks
Mathematical Institute for Machine Learning and Data Science (MIDS)(机器学习与数据科学数学研究所);Catholic University of Eichstätt--Ingolstadt (KU)(埃施斯泰特-因戈尔施塔特天主教大学);Mathematical Institute(数学研究所)