Two Exponential Formulas for $\alpha$-Times Integrated Semigroups $\boldsymbol{(\alpha} \boldsymbol{\in} \boldsymbol{\mathbb{R}^ + )}$

Abstract

In this paper $X$ is a Banach space, $\left( {S(t)}\right) _{t\geq 0}$ is non-dege\-ne\-ra\-te $\alpha -$times integrated, exponentially bounded semigroup on $X$ $(\alpha \in \mathbb{R}^{+}),$ $M\geq 0$ and $\omega _{0}\in \mathbb{R}$ are constants such that $\left\| {S(t)}\right\| \leqslant Me^{\omega _{0}t}$ for all $t\geq 0,$ $\gamma $ is any positive constant greater than $\omega _{0},$ $\Gamma $ is the Gamma-function, $(C,\beta )-\lim $ is the Ces\`{a}ro-$\beta $ limit. Here we prove that
\begin{equation*}
\mathop {\lim }\limits_{n\rightarrow \infty }\frac{1}{{\Gamma
(\alpha )}} \int\limits_{0}^{T}{(T-s)^{\alpha -1}\left(
{\frac{{n+1}}{s}}\right) ^{n+1}R^{n+1}\left(
{\frac{{n+1}}{s},A}\right) x\,ds=S(T)x,}
\end{equation*}
for every $x\in X,$ and the limit is uniform in $T>0$ on any bounded interval. Also we prove that
\begin{equation*}
S(t)x=\frac{1}{{2\pi i}}(C,\beta )-\mathop {\lim }\limits_{\omega
\rightarrow \infty }\int\limits_{\gamma -i\omega }^{\gamma
+i\omega }{ e^{\lambda t}\frac{{R(\lambda ,A)x}}{{\lambda
^{\alpha }}}\,d\lambda },
\end{equation*}
for every $x\in X,\,\,\beta >0$ and $t\geq 0.$

2000 Mathematics Subject Classification. 47D06, 47D60, 47D62