View source for Almost-periodic analytic function

An analytic function $f(s)$, $s=\sigma+i\tau$, regular in a strip $-\infty\leqslant\alpha<\sigma<\beta\leqslant+\infty$, and expandable into a series
\begin{equation}
\sum a_ne^{i\lambda_ns},
\end{equation}

where the $a_n$ are complex and the $\lambda_n$ are real numbers. A real number $\tau$ is called an $\varepsilon$-almost-period of $f(s)$ if for all points of the strip $(\alpha, \beta)$ the inequality

\begin{equation}
|f(s+i\tau) - f(s)|<\varepsilon
\end{equation}

holds. An almost-periodic analytic function is an analytic function that is regular in a strip $(\alpha, \beta)$ and possesses a relatively-dense set of $\varepsilon$-almost-periods for every $\varepsilon>0$. An almost-periodic analytic function on a closed strip $\alpha\leqslant\sigma\leqslant\beta$ is defined similarly. An almost-periodic analytic function on a strip $[\alpha, \beta]$ is a uniformly almost-periodic function of the real variable $\tau$ on every straight line in the strip and it is bounded in $[\alpha, \beta]$, i.e. on any interior strip. If a function $f(s)$, regular in a strip $(\alpha, \beta)$, is a uniformly almost-periodic function on at least one line $\sigma=\sigma_0$ in the strip, then boundedness of $f(s)$ in $[\alpha, \beta]$ implies its almost-periodicity on the entire strip $[\alpha, \beta]$. Consequently, the theory of almost-periodic analytic functions turns out to be a theory analogous to that of almost-periodic functions of a real variable (cf. [[Almost-periodic function|almost-periodic function]]). Therefore, many important results of the latter theory can be easily carried over to almost-periodic analytic functio
ns: the uniqueness theorem, Parseval's equality, rules of operation with Dirichlet series, the approximation theorem, and several other theorems.

====References====
<table><TR><TD valign="top">[1]</TD> <TD valign="top">  H. Bohr,   "Almost-periodic functions" , Chelsea, reprint  (1947)  (Translated from German)</TD></TR><TR><TD valign="top">[2]</TD> <TD valign="top">  B.M. Levitan,   "Almost-periodic functions" , Moscow  (1953)  pp. Chapt. 7  (In Russian)</TD></TR></table>



====Comments====
The hyphen between almost and periodic is sometimes dropped.

====References====
<table><TR><TD valign="top">[a1]</TD> <TD valign="top">  C. Corduneanu,   "Almost periodic functions" , Interscience  (1961)  pp. Chapt. 3</TD></TR></table>