Czechoslovak Mathematical Journal, Vol. 51, No. 3, pp. 505-522, 2001

Measure of noncompactness of linear operators between spaces of sequences that are $(\bar N,q)$ summable or bounded

E. Malkowsky, V. Rakocevic

E. Malkowsky, Mathematisches Institut, Universitat Giessen, Arndtstrasse 2, D-35392 Giessen, Germany, e-mail: Malkowsky@math.uni-giessen.de, ema@bankerinternet; V. Rakocevic, Faculty of Philosophy, Department of Mathematics, University of Nis, Cirila i Metodija 2, 18000 Nis, Yugoslavia, e-mail: vrakoc@bankerinter.net

Abstract: In this paper we investigate linear operators between arbitrary BK spaces $X$ and spaces $Y$ of sequences that are $\Nq$ summable or bounded. We give necessary and sufficient conditions for infinite matrices $A$ to map $X$ into $Y$. Further, the Hausdorff measure of noncompactness is applied to give necessary and sufficient conditions for $A$ to be a compact operator.

Keywords: BK spaces, bases, matrix transformations, measure of noncompactness

Classification (MSC 2000): 40H05, 46A45, 47B07


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