Bounded sequence-to-function Hausdorff transformations

Author:

Georgakis Constantine

Abstract

Let \[ ( T a ) ( y ) = n = 0 ( y ) n g ( n ) ( y ) n ! a n , y 0 \left ( {Ta} \right )\left ( y \right ) = \sum \limits _{n = 0}^\infty {{{\left ( { - y} \right )}^n}} \frac {{{g^{\left ( n \right )}}\left ( y \right )}}{{n!}}{a_{n,\quad }}\quad y \geq 0 \] be the sequence-to-function Hausdorff transformation generated by the completely monotone function g g or, what is equivalent, the Laplace transform of a finite positive measure σ \sigma on [ 0 , ) [0,\infty ) . It is shown that for 1 p 1 \leq p \leq \infty , T T is a bounded transformation of l p {l^p} with weight Γ ( n + s + 1 ) / n ! \Gamma \left ( {n + s + 1} \right ) / n! into L p [ 0 , ) {L^p}[0,\infty ) with weight y s , s > 1 {y^s},s > - 1 , whose norm T = 0 t ( 1 + s ) / p d σ ( t ) = C ( p , s ) \left \| T \right \| = \int _0^\infty {{t^{ - \left ( {1 + s} \right ) / p}}} d\sigma \left ( t \right ) = C\left ( {p,s} \right ) if and only if C ( p , s ) > C\left ( {p,s} \right ) > \infty , and that for 1 > p > , T a p , s > C ( p , s ) a p , s 1 > p > \infty ,{\left \| {Ta} \right \|_{p,s}} > C\left ( {p,s} \right ){\left \| a \right \|_{p,s}} unless a n {a_n} is a null sequence. Furthermore, if 1 > p > r > , 0 > λ > 1 1 > p > r > \infty ,\,\;0 > \lambda > 1 and σ \sigma is absolutely continuous with derivatives ψ \psi such that the function ψ r ( t ) = t 1 / r ψ ( t ) {\psi _r}\left ( t \right ) = {t^{ - 1 / r}}\psi \left ( t \right ) belongs to L 1 / λ [ 0 , ) {L^{1 / \lambda }}[0,\infty ) , then the transformation ( T λ a ) ( y ) = y 1 λ ( T a ) ( y ) \left ( {{T_\lambda }a} \right )\left ( y \right ) = {y^{1 - \lambda }}\left ( {Ta} \right )\left ( y \right ) is bounded from l p {l^p} to L r [ 0 , ) {L^r}[0,\infty ) and has norm T λ ψ r 1 / λ \left \| {{T_\lambda }} \right \| \leq {\left \| {{\psi _r}} \right \|_{1 / \lambda }} . The transformation T T includes in particular the Borel transform and that of generalized Abel means. These results constitute an improved analogue of a theorem of Hardy concerning the discrete Hausdorff transformation on l p {l^p} which corresponds to a totally monotone sequence, and lead to improved forms of some inequalities of Hardy and Littlewood for power series and moment sequences.

Publisher

American Mathematical Society (AMS)

Subject

Applied Mathematics,General Mathematics

Reference11 articles.

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2. An inequality for Hausdorff means;Hardy, G. H.;J. London Math. Soc.,1943

3. G. H. Hardy and J. E. Littlewood, Elementary theorems concerning power series and moment constants, J. für Mat. 157 (1927), 141-158.

4. G. H. Hardy, J. E. Littlewood and G. Pölya, Inequalities, Cambridge Univ. Press, 1967.

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